{"id":39,"date":"2019-08-09T20:58:15","date_gmt":"2019-08-09T20:58:15","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/chapter\/unit-1-the-endocrine-system\/"},"modified":"2024-04-09T23:29:13","modified_gmt":"2024-04-09T23:29:13","slug":"unit-1-the-endocrine-system","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/chapter\/unit-1-the-endocrine-system\/","title":{"raw":"Unit 1: The Endocrine System","rendered":"Unit 1: The Endocrine System"},"content":{"raw":"<div class=\"textbox shaded\">\r\n<p style=\"text-align: justify\"><strong>Unit Outline<\/strong><\/p>\r\n<p style=\"text-align: justify\"><a href=\"#1\"><strong>Part 1:<\/strong> General properties of the endocrine system<\/a><\/p>\r\n\r\n<ul>\r\n \t<li><a href=\"#1-1a\">Introduction: the two general categories of glands in the body<\/a><\/li>\r\n \t<li><a href=\"#1-1b\">General functions of hormones<\/a><\/li>\r\n \t<li><a href=\"#1-1c\">Hormone secretion: regulation and stimuli<\/a><\/li>\r\n \t<li><a href=\"#1-1d\">Types of hormones<\/a><\/li>\r\n \t<li><a href=\"#1-1e\">Pathways of hormone action<\/a><\/li>\r\n \t<li><a href=\"#1-1f\">Comparison of Endocrine and Nervous systems<\/a><\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\"><a href=\"#2\"><strong>Part 2:<\/strong> Major endocrine organs and their secretions<\/a><\/p>\r\n\r\n<ul>\r\n \t<li><a href=\"#1-2a\">Hypothalamus and pituitary glands<\/a><\/li>\r\n \t<li><a href=\"#1-2b\">Thyroid gland<\/a><\/li>\r\n \t<li><a href=\"#1-2c\">Parathyroid gland<\/a><\/li>\r\n \t<li><a href=\"#1-2d\">The adrenal glands<\/a><\/li>\r\n \t<li><a href=\"#1-2e\">The endocrine pancreas<\/a><\/li>\r\n \t<li><a href=\"#1-2f\">Endocrine functions of the ovaries and testes<\/a><\/li>\r\n \t<li><a href=\"#1-2g\">Endocrine functions of the stomach and duodenum<\/a><\/li>\r\n \t<li><a href=\"#1-2h\">Thymus and pineal gland<\/a><\/li>\r\n \t<li><a href=\"#1-2i\">The special nature of prostaglandins<\/a><\/li>\r\n<\/ul>\r\n<a href=\"#1-3\"><strong>Part 3:<\/strong> Summary of Glands, Hormones, their Stimuli, Targets and Effects<\/a>\r\n<h2><a href=\"#P\">Practice Questions<\/a><\/h2>\r\n<\/div>\r\n<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><strong>Learning Objectives<\/strong><\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n\r\nAt the end of this unit, you should be able to:\r\n<p class=\"hanging-indent\"><strong>I.<\/strong> Define \u201cgland\u201d.<\/p>\r\n<p class=\"hanging-indent\"><strong>II.<\/strong> Distinguish between endocrine glands and exocrine glands.<\/p>\r\n<p class=\"hanging-indent\"><strong>III.<\/strong> Describe the purpose and regulation of hormone secretion.<\/p>\r\n<p class=\"hanging-indent\"><strong>IV.<\/strong> Describe stimuli for hormone secretion.<\/p>\r\n<p class=\"hanging-indent\"><strong>V.<\/strong> Describe the main categories of hormones, and how this relates to their receptors and signaling pathways.<\/p>\r\n<p class=\"hanging-indent\"><strong>VI.<\/strong> Compare and contrast the nervous and endocrine systems.<\/p>\r\n<p class=\"hanging-indent\"><strong>VII.<\/strong> Identify on a diagram of the human body the locations of important endocrine glands.<\/p>\r\n<p class=\"hanging-indent\"><strong>VIII.<\/strong> Describe the hypothalamus and pituitary glands and their interrelationship.<\/p>\r\n<strong>IX.<\/strong> Describe the function and secretion of hormones released by the pituitary gland.\r\n\r\n<strong>X.<\/strong> Describe the function and secretion of hormones released by the thyroid gland.\r\n<p class=\"hanging-indent\"><strong>XI.<\/strong> Describe the function and secretion of hormones released by the parathyroid glands.<\/p>\r\n<p class=\"hanging-indent\"><strong>XII.<\/strong> Describe the function and secretion of hormones released by the adrenal gland.<\/p>\r\n<p class=\"hanging-indent\"><strong>XIII.<\/strong> Describe the function and secretion of hormones released by the pancreas.<\/p>\r\n<p class=\"hanging-indent\"><strong>XIV.<\/strong> Name the hormones produced by the following glands and describe their actions: ovaries, testes, stomach, duodenum, thymus and pineal gland.<\/p>\r\n<p class=\"hanging-indent\"><strong>XV.<\/strong> Describe prostaglandins, referring to their composition, where they are produced, where they generally have an effect, and four effects.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><strong>Learning Objectives and Guiding Questions<\/strong><\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n\r\nAt the end of this unit, you should be able to complete all the following tasks, including answering the guiding questions associated with each task.\r\n<p class=\"hanging-indent\"><strong>I.<\/strong> Define \u201cgland\u201d.<\/p>\r\n<p class=\"hanging-indent\"><strong>II.<\/strong> Distinguish between endocrine glands and exocrine glands.<\/p>\r\n\r\n<ol>\r\n \t<li>Describe the different means by which exocrine and endocrine glands release their secretions.<\/li>\r\n \t<li>Identify the general difference between the types of secretions that these two types of glands secrete and name two examples of secretions from each type of gland.<\/li>\r\n \t<li>Name two organs in the body that have both exocrine and endocrine functions. Identify the exocrine and endocrine secretions of one of these organs.<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>III.<\/strong> Describe the purpose and regulation of hormone secretion.<\/p>\r\n\r\n<ol>\r\n \t<li>Specify the fundamental function of the endocrine system (include the definition of homeostasis).<\/li>\r\n \t<li>Describe six overall functions of hormones.<\/li>\r\n \t<li>Name and describe the type of feedback <span style=\"font-family: inherit;font-size: inherit\">mechanism <\/span>that is most commonly involved in hormone regulation. Identify the \"output\" of this feedback <span style=\"font-family: inherit;font-size: inherit\">mechanism<\/span>.<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>IV.<\/strong> Describe stimuli for hormone secretion.<\/p>\r\n\r\n<ol>\r\n \t<li>Compare and contrast the three stimuli for hormone release: humoral, hormonal and nervous<\/li>\r\n \t<li>Describe three examples of hormones that have humoral stimuli.\r\n<ul>\r\n \t<li>Name the hormone, the organ that releases the hormone and the compound which is controlled by the hormone.<\/li>\r\n \t<li>Identify whether these are positive or negative feedback mechanisms.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>Describe one example of a hormone that is controlled by levels of other hormone(s).\r\n<ul>\r\n \t<li>Name the hormone and the organ that releases it.<\/li>\r\n \t<li>Name the organs that release hormones that control the release of this hormone<\/li>\r\n \t<li>Describe how the levels of the first hormone and those of the controlling hormones are related to each other<\/li>\r\n \t<li>Identify whether this is a positive or negative feedback mechanism.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>V.<\/strong> Describe the main categories of hormones, and how this relates to their receptors and signaling pathways.<\/p>\r\n\r\n<ol>\r\n \t<li>Explain the basis upon which hormones are divided into two major groups.<\/li>\r\n \t<li>Name and describe the three types of hormones.\r\n<ul>\r\n \t<li>Identify from which compounds each type is derived.<\/li>\r\n \t<li>Name two examples of each type and actions of each example.<\/li>\r\n \t<li>Identify which type of hormone has the longest half-life and explain the reason for this difference.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>Explain why, although they circulate throughout the body, hormones are able to target specific cells.<\/li>\r\n \t<li>Name five responses that may occur when a hormone successfully interacts with a cell.<\/li>\r\n \t<li>Distinguish between intracellular and extracellular receptors\r\n<ul>\r\n \t<li>For each type of receptor, identify the location (inside or on the cell membrane), and the type of hormone with which they interact (i.e., whether lipid or amino acid based).<\/li>\r\n \t<li>Explain why the type of receptor used by a particular hormone is related to the hydrophilic nature of the hormone.<\/li>\r\n \t<li>Give two examples of hormones that interact with each of the two types of receptor.<\/li>\r\n \t<li>Distinguish between the general mechanism that occurs after hormones interact with each of the two types of receptors.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>VI.<\/strong> Compare and contrast the nervous and endocrine systems.<\/p>\r\n\r\n<ol>\r\n \t<li>Identify the type of intercellular communication each system uses.<\/li>\r\n \t<li>Describe the anatomical relationship between the sending and receiving cells in each system.<\/li>\r\n \t<li>Identify which system has the more rapid and specific method of message transmission and explain the reason for this.<\/li>\r\n \t<li>Differentiate between the general purposes of the two systems (i.e., which type of body function is mainly governed by each type).<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>VII.<\/strong> Identify on a diagram of the human body the locations of each of the following glands (or parts of glands):<\/p>\r\n\r\n<ol>\r\n \t<li>Pineal gland<\/li>\r\n \t<li>Thymus<\/li>\r\n \t<li>Hypothalamus<\/li>\r\n \t<li>Adrenal glands<\/li>\r\n \t<li>Adrenal cortex<\/li>\r\n \t<li>Adrenal medulla<\/li>\r\n \t<li>Anterior pituitary<\/li>\r\n \t<li>Posterior pituitary<\/li>\r\n \t<li>Pancreatic islets<\/li>\r\n \t<li>Thyroid<\/li>\r\n \t<li>Ovaries<\/li>\r\n \t<li>Testes<\/li>\r\n \t<li>Parathyroid glands<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>VIII.<\/strong> Describe the hypothalamus and pituitary glands and their interrelationship.<\/p>\r\n\r\n<ol>\r\n \t<li>Justify the basis for labelling the hypothalamus-pituitary complex as the \u201ccommand centre\u201d of the endocrine system.<\/li>\r\n \t<li>Describe (or draw) the location of the hypothalamus and the anterior pituitary gland, and the anatomical connection between the two glands, including the nature of the vascular connection.<\/li>\r\n \t<li>Describe how a signal is sent from the hypothalamus to the anterior pituitary, to either inhibit or stimulate the release of an anterior pituitary hormone.<\/li>\r\n \t<li>Name and describe the functions of six hypothalamic hormones that control the secretions of the anterior pituitary.<\/li>\r\n \t<li>Describe (or draw) the location of the hypothalamus and the posterior pituitary gland, and the anatomical connection between the two glands, including the nature of the neural connection.<\/li>\r\n \t<li>Name the two hypothalamic hormones that are stored in and secreted from the posterior pituitary.<\/li>\r\n<\/ol>\r\n<strong>IX.<\/strong> Describe the function and secretion of hormones released by the pituitary gland.\r\n<ol>\r\n \t<li>Explain what is meant by four of the anterior pituitary hormones being referred to as \u201ctropic\u201d hormones.<\/li>\r\n \t<li>Name and describe the functions of the two anterior pituitary hormones that do not control the secretion of other endocrine glands.<\/li>\r\n \t<li>Describe how the levels of these hormones are controlled.<\/li>\r\n \t<li>Name and describe the actions of the four tropic hormones released by the anterior pituitary.<\/li>\r\n \t<li>Describe where the hormones that the posterior pituitary secretes are actually produced, and how they are transported to the posterior pituitary.<\/li>\r\n \t<li>Name and describe the actions of the two hormones released by the posterior pituitary.<\/li>\r\n \t<li>Describe how the levels of these hormones are controlled.<\/li>\r\n<\/ol>\r\n<strong>X.<\/strong> Describe the function and secretion of hormones released by the thyroid gland.\r\n<ol>\r\n \t<li>Describe the location of the thyroid gland.<\/li>\r\n \t<li>Name the two hormones released by the thyroid gland.<\/li>\r\n \t<li>Describe the stimulus for, and control of, the release of thyroid hormone.<\/li>\r\n \t<li>Name the two compounds that are grouped under the term \u201cthyroid hormone\u201d.<\/li>\r\n \t<li>Name and define the bodily process that is increased by the release of thyroid hormone.<\/li>\r\n \t<li>State four other processes for which thyroid hormone is required.<\/li>\r\n \t<li>Describe the stimulus for, control and action of, calcitonin. Identify the type of feedback mechanism involved.<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>XI.<\/strong> Describe the function and secretion of hormones released by the parathyroid glands.<\/p>\r\n\r\n<ol>\r\n \t<li>Describe the location of the parathyroid glands.<\/li>\r\n \t<li>Name and describe the actions of the parathyroid hormone.<\/li>\r\n \t<li>Describe the stimulus for and control of the release of parathyroid hormone. Identify the type of feedback <span style=\"font-family: inherit;font-size: inherit\">mechanism <\/span>involved.<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>XII.<\/strong> Describe the function and secretion of hormones released by the adrenal gland.<\/p>\r\n\r\n<ol>\r\n \t<li>Describe the location and the two general divisions of the adrenal gland.<\/li>\r\n \t<li>Name the three general classes of hormones produced by the adrenal cortex.<\/li>\r\n \t<li>Identify the major mineralocorticoid and describe the stimuli for its release, and the effects of its action.<\/li>\r\n \t<li>Identify the major glucocorticoid and describe the stimuli for its release, and the effects of its action.<\/li>\r\n \t<li>Name and describe the actions and stimulus of the third group of hormones released by the adrenal cortex.<\/li>\r\n \t<li>Name and describe the actions of the two hormones released by the adrenal medulla.<\/li>\r\n \t<li>Name two physical and two psychological stressors.<\/li>\r\n \t<li>Name and describe the three stages of the general adaptation syndrome. For each stage, identify the major hormone involved, its effects and either the purpose of the stage or its end result.<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>XIII.<\/strong> Describe the function and secretion of hormones released by the pancreas.<\/p>\r\n\r\n<ol>\r\n \t<li>Describe the location of the pancreas.<\/li>\r\n \t<li>Explain the exocrine and endocrine nature of the pancreas, including the name of the clusters of cells, and individual cell types that produce insulin and glucagon.<\/li>\r\n \t<li>Define gluconeogenesis, glycogenolysis and glycogenesis.<\/li>\r\n \t<li>Describe the stimulus for the release of, and three actions of, glucagon. Identify the type of feedback mechanism involved.<\/li>\r\n \t<li>Describe the stimulus for the release of, and five actions of, insulin. Identify the type of feedback mechanism involved.<\/li>\r\n \t<li>Name and describe the actions of the counterregulatory hormones (include glucagon).<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>XIV.<\/strong> Name the hormones produced by the following glands and describe their actions: ovaries, testes, stomach, duodenum, thymus and pineal gland.<\/p>\r\n<p class=\"hanging-indent\"><strong>XV.<\/strong> Describe prostaglandins, referring to their composition, where they are produced, where they generally have an effect, and four effects.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<h2><strong><a id=\"1\"><\/a>Part 1. General Properties of the Endocrine System<\/strong><\/h2>\r\n<h5 style=\"text-align: justify\"><strong><a id=\"1-1a\"><\/a>Introduction: The two general categories of glands in the body<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The term \u2018gland\u2019 refers to any organ that produces a secretion. These secretions are produced by specialized cells in the glands from various components in the blood. There are two general categories of glands in the body: exocrine glands and endocrine glands.<\/p>\r\nExocrine glands are very diverse and include the salivary glands, mammary glands, sweat glands, pancreas, stomach, prostate, and several others. Their secretions are also varied - saliva, milk, sweat, digestive [pb_glossary id=\"464\"]enzymes[\/pb_glossary] and fluids to accompany [pb_glossary id=\"465\"]gametes[\/pb_glossary] - just from the glands mentioned above. These glands are called exocrine glands because they have tubes or ducts to carry their secretions from the gland to another part of the body. These ducts may be simple tubes or complex, tree-like groups of ducts. Because of these tubes, the exocrine glands are also known as the ducted glands.\r\n<p style=\"text-align: justify\">On the other hand, endocrine glands do not have ducts. Their secretions, called hormones, are carried to various body tissues by the blood and lymph, where they bind to receptors on target cells, inducing a characteristic response. Endocrine glands are sometimes called the ductless glands, and they all produce substances similar in nature, in that they are all hormones.<\/p>\r\n<p style=\"text-align: justify\">Some organs in the body contain both endocrine tissue and exocrine tissue. These organs include the pancreas, stomach and small intestine, all of which produce both hormones and digestive enzymes. The exocrine function of the pancreas (i.e., secretion of digestive enzymes into the duodenum) will be studied during the section on digestion. The endocrine function of the pancreas (release of the hormones insulin and glucagon, both of which are important in the control of blood sugar levels) will be studied later in this chapter.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"1-1b\"><\/a>General functions of endocrine hormones<\/strong><\/h5>\r\n<p style=\"text-align: justify\">You may never have thought of it this way, but when you send a text message to two friends to meet you at local cafe at six, you\u2019re sending digital signals that (you hope) will affect their behaviour\u2014even though they are some distance away. Similarly, endocrine glands send chemical signals (hormones) to other cells in the body that influence their behaviour. This long-distance intercellular communication, coordination, and control is critical for homeostasis, and it is the fundamental function of the endocrine system.<\/p>\r\n<p style=\"text-align: justify\">Although each has its own specific effects, [pb_glossary id=\"460\"]hormones [\/pb_glossary] generally have the following functions:<\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify\">Some hormones stimulate [pb_glossary id=\"459\"]exocrine glands[\/pb_glossary] to produce their secretions<\/li>\r\n \t<li style=\"text-align: justify\">Some stimulate other [pb_glossary id=\"458\"]endocrine glands[\/pb_glossary] to action<\/li>\r\n \t<li style=\"text-align: justify\">Some affect the growth, development and personality of an individual<\/li>\r\n \t<li style=\"text-align: justify\">Some regulate body chemistry such as the metabolism of cells<\/li>\r\n \t<li style=\"text-align: justify\">Some regulate the contraction of muscle tissues and nervous stimulation<\/li>\r\n \t<li style=\"text-align: justify\">Some control reproductive processes<\/li>\r\n<\/ul>\r\n<h5><strong><a id=\"1-1c\"><\/a>Hormonal Secretion: Regulation and Stimuli<\/strong><\/h5>\r\n<strong>Regulation of hormone secretion: <\/strong>Homeostasis is the condition in which the body\u2019s internal environment remains relatively constant within limits. One of the main functions of the endocrine system is to aid in the maintenance of homeostasis. To prevent abnormal hormone levels and a potential disease state, hormone levels must be tightly controlled. The body maintains this control by balancing hormone production and degradation. Feedback mechanisms govern the initiation and maintenance of most hormone secretion in response to various stimuli.\r\n<p style=\"text-align: justify\">The concept of homeostasis and the mechanisms of feedback mechanisms were presented in Homeostasis unit of the Biology 1103\/1109 textbook (for review, refer to: <a href=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/chapter\/unit-8-homeostasis\/\">https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/chapter\/unit-8-homeostasis\/<\/a>). Recall that there are two types of feedback mechanisms: positive and negative. Positive feedback mechanisms intensify a change in the body\u2019s physiological condition rather than reversing it and result in a definite end event. An example of a hormonally based positive feedback mechanism involves the release of oxytocin during childbirth. The initial release of oxytocin begins to signal the uterine muscles to contract, which pushes the fetus toward the cervix, causing it to stretch. This, in turn, signals the [pb_glossary id=\"391\"]pituitary gland[\/pb_glossary] to release more [pb_glossary id=\"471\"]oxytocin[\/pb_glossary], causing labour contractions to intensify. This will bring about the final event of childbirth, after which the release of oxytocin decreases.<\/p>\r\n<p style=\"text-align: justify\">However, the more common method of hormone regulation is the negative feedback mechanism, which generally is involved in the continual maintenance of a characteristic within limits. Hormonally based negative feedback mechanisms are characterized by the inhibition of further secretion of a hormone in response to adequate levels of that hormone (as determined by the amount of the hormone in the blood, or by the extent of the effect that the hormone has had). This allows blood levels of the hormone to be regulated within a narrow range.<\/p>\r\n<strong>Stimuli for hormonal secretion: <\/strong>The stimulus for the levels of a particular hormone can be humoral, i.e., blood levels of non-hormone chemicals such as nutrients or ions. Changes in such levels can cause the release or inhibition of a hormone (under negative feedback control) to maintain homeostasis. For example, [pb_glossary id=\"409\"]osmoreceptors [\/pb_glossary] in the [pb_glossary id=\"392\"]hypothalamus [\/pb_glossary] detect changes in blood [pb_glossary id=\"410\"]osmolarity [\/pb_glossary] (the concentration of solutes in the blood plasma) and will signal the hypothalamus to release greater or lesser amounts of antidiuretic hormone (ADH) to keep the levels of solutes in the blood within normal limits. The control of blood glucose levels by the pancreas is another example of such stimulation. Responding directly to the level of glucose in the blood, cells in the pancreas release appropriate amounts of the hormones insulin and glucagon to maintain normal blood glucose levels. A final example of response to the level of a nutrient or ion in the blood is the regulation of levels of calcium by the parathyroid gland, which responds to changes in calcium levels in the blood with the secretion of varying levels of parathyroid hormone. All these mechanisms will be covered in greater detail later in this chapter.\r\n<p style=\"text-align: justify\">The stimulus for the secretion of a hormone may also be the presence of another hormone produced by a different endocrine gland. Such hormonal stimuli often involve the hypothalamus, which produces releasing and inhibiting hormones that control the secretion of a variety of pituitary hormones, that in turn, may affect other endocrine glands in the body. These secretions are also controlled through negative feedback mechanisms. An example of such a negative feedback mechanism is the release of [pb_glossary id=\"412\"]glucocorticoid [\/pb_glossary] hormones from the [pb_glossary id=\"446\"]adrenal glands[\/pb_glossary], as directed by the hypothalamus and pituitary gland (this will also be covered in more detail later in this chapter). As the secretion of glucocorticoid from the adrenal glands cause concentrations of this hormone in the blood to rise, the hypothalamus and pituitary gland reduce their release of hormones that caused this secretion, thus signaling to the adrenal glands to decrease glucocorticoid secretion (<a class=\"rId8\" href=\"https:\/\/pressbooks.bccampus.ca\/dcbiol12031209\/chapter\/17-2-hormones\/\"><span class=\"import-Hyperlink\">Figure<\/span><\/a> 1).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1117\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2019\/04\/image1.jpeg\" alt=\"image\" width=\"1117\" height=\"1094\" \/> <strong>Figure 1. Negative Feedback Mechanism.<\/strong> The release of adrenal glucocorticoids is stimulated by the release of hormones from the hypothalamus and pituitary gland. This signaling is inhibited when glucocorticoid levels become elevated by causing negative signals to the pituitary gland and hypothalamus.[\/caption]\r\n<h5><strong><a id=\"1-1d\"><\/a>Types of Hormones<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The hormones of the human body can be divided into two major groups on the basis of their chemical structure. Hormones derived from amino acids include amines, peptides, and proteins. Those derived from lipids include steroids (<span class=\"import-Hyperlink\">Table<\/span><span class=\"import-Hyperlink\"> 1<\/span>). These chemical groups affect a hormone\u2019s distribution, the type of receptors it binds to, and other aspects of its function.<\/p>\r\n<strong>Amine Hormones<\/strong>\r\n<p style=\"text-align: justify\">Hormones derived from the modification of amino acids are referred to as amine hormones. Examples these include the metabolism-regulating thyroid hormones, as well epinephrine and norepinephrine, which play a role in the fight-or-flight response.<\/p>\r\n<strong>Peptide and Protein Hormones<\/strong>\r\n<p style=\"text-align: justify\">Whereas the amine hormones are derived from a single [pb_glossary id=\"447\"]amino acid[\/pb_glossary], peptide and protein hormones consist of multiple amino acids that link to form an amino acid chain. Peptide hormones consist of short chains of amino acids, whereas protein hormones are longer polypeptides.<\/p>\r\n<p style=\"text-align: justify\">An example of a peptide hormone is antidiuretic hormone (ADH), a pituitary hormone important in fluid balance. Examples of protein hormones include growth hormone, which is produced by the pituitary gland, and follicle-stimulating hormone (FSH), which helps stimulate the maturation of eggs in the ovaries and sperm in the testes.<\/p>\r\n<strong>Steroid Hormones<\/strong>\r\n<p style=\"text-align: justify\">The primary hormones derived from lipids are [pb_glossary id=\"448\"]steroids[\/pb_glossary]. Steroid hormones are derived from the lipid cholesterol. For example, the reproductive hormones testosterone and the estrogens\u2014which are produced by the gonads (testes and ovaries)\u2014are steroid hormones. The adrenal glands produce the steroid hormone aldosterone, which is involved in osmoregulation, and cortisol, which plays a role in metabolism.<\/p>\r\n<p style=\"text-align: justify\">Like cholesterol, steroid hormones are not soluble in water (they are [pb_glossary id=\"469\"]hydrophobic[\/pb_glossary]). Because blood is water-based, lipid-derived hormones must travel to their target cell bound to a transport protein. This more complex structure extends the half-life of steroid hormones to much longer than that of hormones derived from amino acids. A hormone\u2019s half-life is the time required for half the concentration of the hormone to be degraded. For example, the lipid-derived hormone [pb_glossary id=\"472\"]cortisol[\/pb_glossary] has a half-life of approximately 60 to 90 minutes. In contrast, the amino acid\u2013derived hormone [pb_glossary id=\"449\"]epinephrine [\/pb_glossary] has a half-life of approximately one minute.<\/p>\r\n\r\n<h5><strong><a id=\"1-1e\"><\/a>Pathways of Hormone Action<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Although a given hormone may travel throughout the body in the bloodstream, it will affect the activity only of its target cells; that is, cells with receptors for that particular hormone. The message a hormone sends is received by a\u00a0<strong>[pb_glossary id=\"389\"]hormone receptor[\/pb_glossary]<\/strong>, a protein located either inside the cell or within the cell membrane. The receptor will process the message by initiating other signaling events or cellular\u00a0mechanisms that result in the target cell\u2019s response. Hormone receptors recognize molecules with specific shapes and side groups, and respond only to those hormones that are recognized. The same type of receptor may be located on cells in different body tissues, and trigger somewhat different responses. Thus, the response triggered by a hormone depends not only on the hormone, but also on the target cell.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1046\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image2.jpeg\" alt=\"image\" width=\"1046\" height=\"1329\" \/> <strong>Table 1. Amine, Peptide, Protein, and Steroid Hormone Structure<\/strong> (the structural formulae are not required as examinable material).[\/caption]\r\n<p style=\"text-align: justify\">Once the target cell receives the hormone signal, it can respond in a variety of ways. The response may include the stimulation of protein synthesis, activation or deactivation of enzymes, alteration in the permeability of the cell membrane, altered rates of mitosis and cell growth, and stimulation of the secretion of products. Moreover, a single hormone may be capable of inducing different responses in a given cell.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"937\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image3.jpeg\" alt=\"image\" width=\"937\" height=\"621\" \/> <strong>Figure 2. Binding of Lipid-Soluble Hormones.<\/strong> A steroid hormone directly initiates the production of proteins within a target cell. Steroid hormones easily diffuse through the cell membrane. The hormone binds to its receptor in the cytosol, forming a receptor\u2013hormone complex. The receptor\u2013hormone complex then enters the nucleus and binds to the target gene on the DNA. Transcription of the gene creates a messenger RNA that is translated into the desired protein within the cytoplasm.[\/caption]\r\n\r\n<strong>Pathways Involving Intracellular Hormone Receptors: <\/strong>Intracellular hormone receptors are located inside the cell. Hormones that bind to this type of receptor must be able to cross the cell membrane. Steroid hormones are derived from cholesterol and therefore can readily diffuse through the lipid bilayer of the cell membrane to reach the intracellular receptor (<span class=\"import-Hyperlink\">Figure 2<\/span>). [pb_glossary id=\"450\"]Thyroid [\/pb_glossary] hormones are also lipid-soluble and can enter the cell. Both hormones bind to DNA within the nucleus and trigger protein synthesis. The particular proteins synthesized will exert an effect.\r\n\r\n<strong>Pathways Involving Cell Membrane Hormone Receptors: <\/strong>[pb_glossary id=\"468\"]Hydrophilic[\/pb_glossary], or water-soluble, hormones are unable to diffuse through the lipid bilayer of the cell membrane and must therefore pass on their message to a receptor located at the surface of the cell (Figure 3). Except for thyroid hormones, which are lipid-soluble, all amino acid\u2013derived hormones bind to cell membrane receptors that are located, at least in part, on the extracellular surface of the cell membrane. Therefore, they do not directly affect the production of proteins, but instead initiate a signaling cascade (a series of sequential activation of enzymes within the cell) that can trigger a wide variety of effects, from nutrient metabolism to the synthesis of different hormones and other products. The effects vary according to the type of target cell and which signaling cascade is activated inside the cell. Examples of hormones that use this mechanism include calcitonin, which is important for bone construction and regulating blood calcium levels, and [pb_glossary id=\"451\"]glucagon[\/pb_glossary], which affects blood glucose levels.\r\n<p style=\"text-align: justify\">Overall, such signaling cascades significantly increase the efficiency, speed, and specificity of the hormonal response, as thousands of signaling events can be initiated simultaneously in response to a very low concentration of hormone in the bloodstream, so the action of the hormone can be rapid and substantial. Additionally, the duration of this type of hormone signal is short.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"965\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image4.jpeg\" alt=\"image\" width=\"965\" height=\"731\" \/> <strong>Figure 3. Binding of Water-Soluble Hormones.<\/strong> Water-soluble hormones cannot diffuse through the cell membrane. These hormones must bind to a surface cell-membrane receptor. The receptor then initiates a cell-signaling pathway within the cell involving G proteins, adenylyl cyclase, the secondary messenger cyclic AMP (cAMP), and protein kinases. In the final step, these protein kinases phosphorylate proteins in the cytoplasm. This activates proteins in the cell that carry out the changes specified by the hormone. (The specific steps of the cell-signaling pathway are not required as examinable material).[\/caption]\r\n<h5 style=\"text-align: justify\"><strong><a id=\"1-1f\"><\/a>Comparison of the endocrine and nervous systems<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Communication is a process in which a sender transmits signals to one or more receivers to control and coordinate actions. The part that the endocrine system plays in this has been stated, however in the human body, another major organ system participates in relatively \u201clong distance\u201d communication: the nervous system. Together, these two systems are primarily responsible for maintaining [pb_glossary id=\"452\"]homeostasis [\/pb_glossary] in the body. Although both systems function to allow communication within the body, there are some significant differences in the anatomy and physiology and thus how the function is carried out between the endocrine and nervous systems.<\/p>\r\n<p style=\"text-align: justify\">The <strong>nervous system<\/strong> uses two types of intercellular communication\u2014electrical and chemical signaling\u2014either by the direct action of an electrical potential, or in the latter case, through the action of chemical neurotransmitters such as serotonin or [pb_glossary id=\"454\"]norepinephrine[\/pb_glossary]. [pb_glossary id=\"453\"]Neurotransmitters [\/pb_glossary] act locally and rapidly. When an electrical signal in the form of an action potential arrives at a synaptic terminal, it results in the release of neurotransmitters, which diffuse across the synaptic cleft (the gap between a sending neuron and a receiving neuron or muscle cell). Once the neurotransmitters interact (bind) with receptors on the receiving (post-synaptic) cell, the receptor stimulation is transduced into a response such as continued electrical signaling or modification of cellular response. The target cell responds within milliseconds of receiving the chemical \u201cmessage\u201d; this response then ceases very quickly once the neural signaling ends. In this way, neural communication enables body functions that involve quick, brief actions, such as movement, sensation, and cognition.<\/p>\r\n<p style=\"text-align: justify\">In contrast, the <strong>endocrine system <\/strong>uses just one method of communication: chemical signaling through <strong>hormones<\/strong>, which are secreted into the extracellular fluid. As previously stated, hormones are transported (primarily) via the bloodstream throughout the body, where they bind to receptors on target cells, inducing a characteristic response. As a result, endocrine signaling requires more time than neural signaling to prompt a response in target cells, though the precise amount of time varies with different hormones. For example, the hormones released when you are confronted with a dangerous or frightening situation, called the fight-or-flight response, occur by the release of adrenal hormones\u2014[pb_glossary id=\"449\"]epinephrine [\/pb_glossary] and [pb_glossary id=\"454\"]norepinephrine[\/pb_glossary]\u2014within seconds. In contrast, it may take up to 48 hours for target cells to respond to certain reproductive hormones. Similarly, due to the mechanism of transmission of hormonal signals, the effect tends to last longer than a nervous stimulation.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"171\"]<a href=\"http:\/\/openstaxcollege.org\/l\/hormonebind\"><img class=\"\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image5.png\" alt=\"image\" width=\"171\" height=\"170\" \/><\/a> Visit <a href=\"http:\/\/openstaxcollege.org\/l\/hormonebind\">this link<\/a> to watch an animation of the events that occur when a hormone binds to a cell membrane receptor. Direct link: <a href=\"http:\/\/openstaxcollege.org\/l\/hormonebind\">http:\/\/openstaxcollege.org\/l\/hormonebind<\/a>[\/caption]\r\n<p style=\"text-align: justify\">In addition, endocrine signaling is typically less specific than neural signaling. The same hormone may play a role in a variety of different physiological processes depending on the target cells involved. For example, the hormone [pb_glossary id=\"471\"]oxytocin [\/pb_glossary] promotes uterine contractions in women in labour. It is also important in breastfeeding and may be involved in the sexual response and in feelings of emotional attachment in both males and females.<\/p>\r\n<p style=\"text-align: justify\">In general, the nervous system involves quick responses to rapid changes in the external environment, and the endocrine system is usually slower acting\u2014taking care of the internal environment of the body, maintaining homeostasis, and controlling reproduction (Table 2).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"150\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image6.png\" alt=\"image\" width=\"150\" height=\"150\" \/> Watch <a href=\"https:\/\/youtu.be\/eWHH9je2zG4\">this Crash Course video<\/a> for an overview of the endocrine system! Direct link: <a href=\"https:\/\/youtu.be\/eWHH9je2zG4\">https:\/\/youtu.be\/eWHH9je2zG4<\/a>[\/caption]\r\n<p style=\"text-align: justify\">So how does the fight-or-flight response that was mentioned earlier happen so quickly if hormones are usually slower acting? It is because the two systems are connected. It is the fast action of the nervous system in response to the danger in the environment that stimulates the adrenal glands to secrete their hormones. As a result, the nervous system can cause rapid endocrine responses to keep up with sudden changes in both the external and internal environments when necessary.<\/p>\r\n\r\n<table style=\"width: 100%;height: 196px\" border=\"0.5pt solid windowtext\"><caption><strong>Table 2<\/strong>. Major characteristics of endocrine and nervous systems<\/caption>\r\n<thead>\r\n<tr style=\"height: 1pt\">\r\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"col\"><\/th>\r\n<th class=\"TableGrid-C\" style=\"background-color: #d0cece;vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\" scope=\"col\"><strong>Endocrine system<\/strong><\/th>\r\n<th class=\"TableGrid-C\" style=\"background-color: #d0cece;vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\" scope=\"col\"><strong>Nervous system<\/strong><\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\r\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Signaling mechanism(s)<\/th>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Chemical<\/td>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Chemical \/ electrical<\/td>\r\n<\/tr>\r\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\r\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Primary chemical signal<\/th>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Hormones<\/td>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Neurotransmitters<\/td>\r\n<\/tr>\r\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\r\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Distance travelled by chemical signal<\/th>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Long or short<\/td>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Always short<\/td>\r\n<\/tr>\r\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\r\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Response time<\/th>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Fast or slow<\/td>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Always fast<\/td>\r\n<\/tr>\r\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\r\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Duration of response<\/th>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Longer than nervous<\/td>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Very short<\/td>\r\n<\/tr>\r\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\r\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Environment targeted<\/th>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Internal<\/td>\r\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Internal and external<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<h2 style=\"text-align: justify\"><strong><a id=\"2\"><\/a>Part 2. Major endocrine organs and their secretions<\/strong><\/h2>\r\n<p style=\"text-align: justify\">The major endocrine glands are shown in Figure 4, and are listed along with their associated hormones and their effects in <a href=\"#1-3\">Table 3<\/a>.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"696\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image1-10.png\" alt=\"image\" width=\"696\" height=\"598\" \/> <strong>Figure 4. Endocrine System.<\/strong> Endocrine glands and cells are located throughout the body and play an important role in homeostasis.[\/caption]\r\n<h5><strong><a id=\"1-2a\"><\/a>The Hypothalamus and Pituitary Gland<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The hypothalamus\u2013pituitary complex can be thought of as the \u201ccommand centre\u201d of the endocrine system for basically two reasons. Besides secreting several hormones that directly produce responses in target tissues, it secretes hormones that regulate the synthesis and secretion of hormones of other endocrine glands. In addition, the hypothalamus\u2013pituitary complex coordinates the messages of the endocrine and nervous systems. In many cases, a stimulus received by the nervous system must pass through the hypothalamus\u2013pituitary complex to be translated into hormones that can initiate a response.<\/p>\r\n<p style=\"text-align: justify\">The [pb_glossary id=\"392\"]<strong>hypothalamus<\/strong> [\/pb_glossary] is a structure of the diencephalon of the brain located anterior and inferior to the thalamus (Figure 5). The hypothalamus is anatomically and functionally related to the <strong>[pb_glossary id=\"391\"]pituitary gland[\/pb_glossary]<\/strong> (or hypophysis), a bean-sized organ suspended from it by a stem called the [pb_glossary id=\"390\"]<strong>infundibulum<\/strong> [\/pb_glossary] (or pituitary stalk).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1077\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image9.png\" alt=\"image\" width=\"1077\" height=\"626\" \/> <strong>Figure 5. Hypothalamus\u2013Pituitary Complex.<\/strong> The hypothalamus region lies inferior and anterior to the thalamus. It connects to the pituitary gland by the stalk-like infundibulum. The pituitary gland consists of an anterior and posterior lobe, with each lobe secreting different hormones in response to signals from the hypothalamus.[\/caption]\r\n<p style=\"text-align: justify\">The <strong>pituitary gland<\/strong> is cradled within a cup-like hollow in the sphenoid bone of the skull. It consists of two lobes that arise from different parts of embryonic tissue: the anterior pituitary (also known as the adenohypophysis) is glandular tissue that develops from the primitive digestive tract, whereas the posterior pituitary (neurohypophysis) is neural tissue that is essentially an extension of the hypothalamus.<\/p>\r\n<p style=\"text-align: justify\"><strong>Hormonal secretion by the hypothalamus: <\/strong>All of the hormones that the hypothalamus produces either are directly secreted by the hypothalamus and control the release of hormones by the anterior pituitary (six of these will be discussed below) or are stored in and released by the posterior pituitary (there are two, as presently discussed).<\/p>\r\n<p style=\"text-align: justify\"><strong>Hypothalamic control of anterior pituitary gland secretion: <\/strong>The secretion of all hormones from the anterior pituitary is regulated by two classes of hormones secreted by the hypothalamus: releasing hormones that stimulate the secretion of hormones from the anterior pituitary, and inhibiting hormones that inhibit secretion (i.e., the anterior pituitary never increases or decreases the release of one of its hormones, without being signaled to do so by the hypothalamus).<\/p>\r\n<p style=\"text-align: justify\">Hypothalamic hormones that control the anterior pituitary are secreted by neurons in the hypothalamus and enter the anterior pituitary through blood vessels (Figure 6). Within the [pb_glossary id=\"390\"]infundibulum [\/pb_glossary] (the connecting tissue between the hypothalamus and the pituitary) is a bridge of capillaries that connects the hypothalamus to the anterior pituitary. This network, called the <strong>[pb_glossary id=\"393\"]hypophyseal portal system[\/pb_glossary]<\/strong>, allows hypothalamic hormones to be transported to the anterior pituitary without first entering the systemic circulation. Hormones produced by the anterior pituitary in response to these releasing or inhibiting hormones sent by the hypothalamus then enter a secondary capillary plexus, and from there drain into the general circulation.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1154\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image10.png\" alt=\"image\" width=\"1154\" height=\"996\" \/> <strong>Figure 6. Anterior Pituitary.<\/strong> The hypothalamus produces separate hormones that stimulate or inhibit hormone production in the anterior pituitary. Hormones from the hypothalamus reach the anterior pituitary via the hypophyseal portal system.[\/caption]\r\n<p style=\"text-align: justify\">Four of the hormones the hypothalamus produces act as releasing factors which stimulate the secretion of five separate hormones from the anterior pituitary gland (Figure 7). These four releasing hormones are named after the pituitary hormones whose secretions they stimulate:<\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify\">[pb_glossary id=\"1250\"]Adrenocorticotropic hormone releasing hormone[\/pb_glossary] (ACTHRH, or CRH for corticotropin releasing hormone)<\/li>\r\n \t<li style=\"text-align: justify\">[pb_glossary id=\"1249\"]Thyroid stimulating hormone releasing hormone[\/pb_glossary] (TSHRH, or TRH for thyrotropin releasing hormone)<\/li>\r\n \t<li style=\"text-align: justify\">[pb_glossary id=\"1248\"]Growth hormone releasing hormone (GHRH)[\/pb_glossary]<\/li>\r\n \t<li style=\"text-align: justify\">[pb_glossary id=\"1247\"]Gonadotropin releasing hormone (GnRH)[\/pb_glossary], which stimulates the release of\u00a0hormones known as gonadotropins: follicle stimulating hormone (FSH) and luteinizing hormone (LH)<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\">The hypothalamus also produces inhibiting factors, including <em>growth hormone inhibiting hormone<\/em> (GHIH) and <em>prolactin inhibiting hormone<\/em> (PIH).<\/p>\r\n<p style=\"text-align: justify\">Cells of the hypothalamus also produce hormones that are stored in and secreted by the posterior pituitary, rather than being secreted from the hypothalamus itself.\u00a0 The hypothalamus produces the hormones oxytocin and [pb_glossary id=\"473\"]antidiuretic hormone[\/pb_glossary] (Figure 7), both of which are transported, stored in and then released from the posterior pituitary gland (discussed in the section describing secretions of the posterior pituitary) (Fig. 8).<\/p>\r\n\r\n\r\n[caption id=\"attachment_1520\" align=\"aligncenter\" width=\"868\"]<a href=\"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3.png\"><img class=\"wp-image-1520 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3.png\" alt=\"\" width=\"868\" height=\"547\" \/><\/a> <strong>Figure 7. Hormones of the hypothalamus.<\/strong> The hypothalamus releases hormones that either control the release of other hormones from the anterior pituitary, or produces hormones (ADH and oxytocin) that are released by the posterior pituitary.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"957\"]<img class=\"\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image11.png\" alt=\"image\" width=\"957\" height=\"772\" \/> <strong>Figure 8. Posterior Pituitary.<\/strong> Neurosecretory cells in the hypothalamus release oxytocin (OT) or ADH into the posterior lobe of the pituitary gland. These hormones are stored or released into the blood via the capillary plexus.[\/caption]\r\n<p style=\"text-align: justify\"><strong>Hormonal secretion by the anterior pituitary: <\/strong>The anterior pituitary produces several hormones, including [pb_glossary id=\"474\"]growth hormone[\/pb_glossary] (GH) and [pb_glossary id=\"475\"]prolactin[\/pb_glossary], neither of which affect other endocrine glands, and [pb_glossary id=\"476\"]thyroid-stimulating hormone[\/pb_glossary] (TSH), [pb_glossary id=\"1374\"]adrenocorticotropic hormone (ACTH)[\/pb_glossary], [pb_glossary id=\"478\"]follicle-stimulating hormone[\/pb_glossary] (FSH), and [pb_glossary id=\"479\"]luteinizing hormone[\/pb_glossary] (LH). Of the hormones of the anterior pituitary, these last four (TSH, ACTH, FSH, and LH) are collectively referred to as tropic hormones (the suffix \u201ctropic\u201d = \u201cturning towards \/ having an influence on\u201d) because they travel to and affect the function of other endocrine glands.<\/p>\r\n<strong>Growth Hormone: <\/strong>The endocrine system regulates the growth of the human body, protein synthesis, and cellular replication. A major hormone involved in this process is [pb_glossary id=\"474\"]growth hormone[\/pb_glossary] (GH), also called somatotropin (\u201csoma\u201d means body; \u201ctropin\u201d means going towards\/having an effect on) \u2014a protein hormone produced and secreted by the anterior pituitary gland. Its primary function is anabolic; it promotes protein synthesis and tissue building, increases catabolism of fats and generally slows down the catabolism of carbohydrates (thus helping to maintain blood glucose levels) (Figure 9). GH levels are controlled by the release of growth hormone-releasing hormone (GHRH) and growth hormone-inhibiting hormone (GHIH, also known as somatostatin) from the hypothalamus.\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"962\"]<img class=\"\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image12.png\" alt=\"image\" width=\"962\" height=\"816\" \/> <strong>Figure 9. Hormonal Regulation of Growth.<\/strong> Growth hormone (GH) directly accelerates the rate of protein synthesis in skeletal muscle and bones. Insulin-like growth factor 1 (IGF-1) is activated by growth hormone and indirectly supports the formation of new proteins in muscle cells and bone.[\/caption]\r\n\r\n<strong style=\"text-align: justify;font-size: 1em\">Prolactin: <\/strong><span style=\"text-align: justify;font-size: 1em\">As its name implies, <\/span><strong style=\"text-align: justify;font-size: 1em\">[pb_glossary id=\"475\"]prolactin[\/pb_glossary]<\/strong><span style=\"text-align: justify;font-size: 1em\"> (<\/span><strong style=\"text-align: justify;font-size: 1em\">PRL<\/strong><span style=\"text-align: justify;font-size: 1em\">) promotes lactation (milk production) in women. During pregnancy, it contributes to the development of the mammary glands, and after birth, it stimulates the mammary glands to produce breast milk. (As will be noted later, the let-down (release) of milk from the breasts occurs in response to stimulation from [pb_glossary id=\"471\"]oxytocin[\/pb_glossary].)<\/span>\r\n<p style=\"text-align: justify\">In a non-pregnant woman, prolactin secretion is inhibited by prolactin-inhibiting hormone (PIH), which is actually the neurotransmitter dopamine, and is released from neurons in the hypothalamus. Only during pregnancy do prolactin levels rise in response to prolactin-releasing hormone (PRH) from the hypothalamus.<\/p>\r\n<p style=\"text-align: justify\"><strong>The [pb_glossary id=\"408\"]Tropic [\/pb_glossary] Hormones<\/strong><\/p>\r\n<p style=\"text-align: justify\"><strong>Thyroid-Stimulating Hormone: <\/strong>The activity of the thyroid gland is regulated by <strong>[pb_glossary id=\"476\"]thyroid-stimulating hormone[\/pb_glossary]<\/strong> (<strong>TSH<\/strong>), also called thyrotropin, released from the anterior pituitary. In turn, TSH is released from the anterior pituitary in response to thyrotropin-releasing hormone (TRH or TSHRH) from the hypothalamus. As discussed shortly, TSH triggers the secretion of thyroid hormones by the thyroid gland. In a classic negative feedback mechanism, elevated levels of thyroid hormones in the bloodstream then trigger a decrease in production of TRH and subsequently TSH.<\/p>\r\n<p style=\"text-align: justify\"><strong>Adrenocorticotropic Hormone: <\/strong>The <strong>[pb_glossary id=\"1374\"]adrenocorticotropic hormone[\/pb_glossary]<\/strong>\u00a0(<strong>ACTH<\/strong>), also called corticotropin, stimulates the adrenal cortex (the outer layer of the adrenal glands) to secrete corticosteroid hormones such as [pb_glossary id=\"472\"]cortisol[\/pb_glossary].<\/p>\r\n<p style=\"text-align: justify\">The release of ACTH is regulated by the corticotropin-releasing hormone (CRH) from the hypothalamus in response to normal physiologic rhythms (The release of ACTH typically peaks in the morning, and reaches its lowest levels in late evening). A variety of stressors can also influence its release, and the role of ACTH in the stress response is discussed later in this unit.<\/p>\r\n<p style=\"text-align: justify\"><strong>Follicle-Stimulating Hormone and Luteinizing Hormone: <\/strong>Several endocrine glands secrete a variety of hormones that control the development and regulation of the reproductive system (these glands include the anterior pituitary, the adrenal cortex, and the gonads - the testes in males and the ovaries in females). Much of the development of the reproductive system occurs during puberty and is marked by the development of sex-specific characteristics in both male and female adolescents. Puberty is initiated by <strong>[pb_glossary id=\"480\"]gonadotropin[\/pb_glossary]-releasing hormone<\/strong> (<strong>GnRH<\/strong>), a hormone produced and secreted by the hypothalamus. GnRH stimulates the anterior pituitary to secrete <strong>[pb_glossary id=\"394\"]gonadotropins[\/pb_glossary]<\/strong>\u2014hormones that regulate the function of the gonads. The levels of GnRH are regulated through a negative feedback mechanism; high levels of reproductive hormones inhibit the release of GnRH. Throughout life, gonadotropins regulate reproductive function and, in the case of women, the onset and cessation of reproductive capacity.<\/p>\r\n<p style=\"text-align: justify\">The gonadotropins include two hormones: 1) <strong>[pb_glossary id=\"478\"]Follicle-stimulating hormone[\/pb_glossary]<\/strong> (<strong>FSH<\/strong>) which stimulates the production and maturation of sex cells, or gametes (ova in females and sperm in males). FSH also promotes follicular growth; these follicles then release estrogens in the ovaries. 2) <strong>[pb_glossary id=\"479\"]Luteinizing hormone[\/pb_glossary]<\/strong> (<strong>LH<\/strong>) triggers ovulation, as well as the production of [pb_glossary id=\"481\"]estrogens [\/pb_glossary] and [pb_glossary id=\"482\"]progesterone [\/pb_glossary] by the [pb_glossary id=\"483\"]ovaries[\/pb_glossary]. LH stimulates production of [pb_glossary id=\"485\"]testosterone[\/pb_glossary] by the [pb_glossary id=\"484\"]testes[\/pb_glossary].<\/p>\r\n<p style=\"text-align: justify\"><strong>Hormonal secretion by the posterior pituitary: <\/strong>The posterior pituitary is actually an extension of neurons that originate in two specific [pb_glossary id=\"486\"]nuclei [\/pb_glossary] (clusters of neuronal cell bodies) in the hypothalamus. While the cell bodies of these neurons rest in the hypothalamus, their axons descend as the hypothalamic\u2013hypophyseal tract within the [pb_glossary id=\"390\"]infundibulum[\/pb_glossary], and end in axon terminals that comprise the posterior pituitary (Figure 7).<\/p>\r\n<p style=\"text-align: justify\">The posterior pituitary gland does not produce hormones, but rather stores and secretes hormones produced by the hypothalamus. Neuronal cell bodies of one group of cells in the hypothalamus produces the hormone [pb_glossary id=\"471\"]oxytocin[\/pb_glossary], whereas neuronal cell bodies of another group of cells produces [pb_glossary id=\"473\"]antidiuretic hormone[\/pb_glossary] (ADH). These hormones then travel along the axons belonging to the respective neurons into storage sites in the axon terminals of the posterior pituitary. In response to later signals from the hypothalamus, the hormones are then released from the axon terminals into the bloodstream.<\/p>\r\n<p style=\"text-align: justify\"><strong>Oxytocin: <\/strong>When fetal development is complete, the peptide-derived hormone oxytocin (tocia- = \u201cchildbirth\u201d) stimulates uterine contractions and dilation of the cervix. Oxytocin is continually released throughout childbirth through a positive feedback mechanism that continues until birth.<\/p>\r\n<p style=\"text-align: justify\">Although the mother\u2019s high blood levels of oxytocin begin to decrease immediately following birth, oxytocin continues to play a role in maternal and newborn health. First, oxytocin is necessary for the milk ejection reflex (commonly referred to as \u201clet-down\u201d) in breastfeeding women. Secondly, in both males and females, oxytocin is thought to contribute to parent\u2013newborn bonding, known as attachment. In general, oxytocin is also thought to be involved in feelings of love and closeness, as well as in the sexual response.<\/p>\r\n<p style=\"text-align: justify\"><strong>Antidiuretic Hormone (ADH): <\/strong>ADH is an important hormone of the urinary system.\u00a0 The solute concentration of the blood, or blood [pb_glossary id=\"410\"]osmolarity[\/pb_glossary], may change in response to the consumption of certain foods and fluids, as well as in response to disease, injury, medications, or other factors. Blood osmolarity is constantly monitored by <strong>[pb_glossary id=\"409\"]osmoreceptors[\/pb_glossary]<\/strong>\u2014specialized cells within the hypothalamus that are particularly sensitive to the concentration of sodium ions and other solutes.<\/p>\r\n<p style=\"text-align: justify\">In response to high blood osmolarity, which can occur during dehydration or following a very salty meal, the osmoreceptors in the hypothalamus signal the posterior pituitary to release <strong>antidiuretic hormone<\/strong> (<strong>ADH<\/strong>). The target cells of ADH are located in the tubular cells of the kidneys. Its effect is to increase epithelial permeability to water, allowing increased water reabsorption. A greater concentration of water in the blood results in a reduced concentration of solutes. ADH is also known as vasopressin because, in very high concentrations, it causes constriction of blood vessels, which increases blood pressure by increasing peripheral resistance. The release of ADH is controlled by a negative feedback mechanism. As blood osmolarity decreases, the hypothalamic osmoreceptors sense the change and prompt a corresponding decrease in the secretion of ADH. As a result, less water is reabsorbed from the urine filtrate.<\/p>\r\n&nbsp;\r\n\r\n[caption id=\"attachment_38\" align=\"alignnone\" width=\"514\"]<img class=\"wp-image-32 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image4-10-Openstax-anterior-view-thyroid.png\" alt=\"\" width=\"514\" height=\"302\" \/> <strong>Figure 10. Anterior view of thyroid gland.<\/strong>[\/caption]\r\n\r\n&nbsp;\r\n<h5><strong><a id=\"1-2b\"><\/a>The Thyroid Gland<\/strong><\/h5>\r\n<p style=\"text-align: justify\">A butterfly-shaped organ, the <strong>thyroid gland<\/strong> is located anterior to the trachea, just inferior to the larynx (Figure 10). The medial region, called the isthmus, is flanked by wing-shaped left and right lobes. Each of the thyroid lobes are embedded with parathyroid glands, primarily on their posterior surfaces. The thyroid gland produces and secretes two hormones: thyroid hormone and calcitonin.<\/p>\r\n<p style=\"text-align: justify\"><strong>Thyroid Hormone<\/strong><\/p>\r\n<p style=\"text-align: justify\">As with many other hormones, the release of thyroid hormone is under negative feedback control, as a result of stimulation by TSH ([pb_glossary id=\"487\"]thyroid stimulating hormone[\/pb_glossary]) released by the anterior pituitary. Recall that TSH is stimulated in turn by the release of TSHRH (thyroid stimulating hormone releasing hormone) released by the hypothalamus. Thyroid hormone actually consists of two slightly different compounds: T<sub>3<\/sub> (triiodothyronine) and T<sub>4 <\/sub>(thyroxine). These compounds are often referred to as metabolic hormones because their levels influence the body\u2019s basal metabolic rate, which is the amount of energy used by the body to make ATP at rest. When T<sub>3<\/sub> and T<sub>4<\/sub> bind to intracellular receptors, they cause an increase in nutrient breakdown (thus causing a breakdown of fats and carbohydrates), and the increased use of oxygen to produce ATP. In addition, T<sub>3<\/sub> and T<sub>4<\/sub> initiate the transcription of genes involved in glucose oxidation. The process is inefficient, and an increased amount of heat is released as a byproduct of the increased rate of cellular respiration. This so-called calorigenic effect (calor- = \u201cheat\u201d) raises body temperature.<\/p>\r\n<p style=\"text-align: justify\">Adequate levels of thyroid hormones are also required for protein synthesis and for fetal and childhood tissue development and growth. They are especially critical for normal development of the nervous system both <em>in utero<\/em> and in early childhood, and they continue to support neurological function in adults.<\/p>\r\n<p style=\"text-align: justify\">These thyroid hormones also have a complex interrelationship with reproductive hormones, and deficiencies can influence libido, fertility, and other aspects of reproductive function. Finally, thyroid hormones increase the body\u2019s sensitivity to catecholamines (epinephrine and norepinephrine) from the adrenal medulla by upregulation of receptors in the blood vessels and the heart. When levels of T<sub>3<\/sub> and T<sub>4<\/sub> hormones are excessive, this effect accelerates the heart rate, strengthens the heartbeat, and increases blood pressure. Because thyroid hormones regulate metabolism, heat production, protein synthesis, and many other body functions, thyroid disorders can have severe and widespread consequences.<\/p>\r\n<p style=\"text-align: justify\">A symptom of many thyroid disorders is a <strong>[pb_glossary id=\"395\"]goiter[\/pb_glossary]<\/strong>, which is an increase in the overall size of the thyroid gland (Figure 11). Interestingly, a goiter can arise whether the thyroid gland is synthesizing too much or too little of thyroid hormone.<\/p>\r\n<p style=\"text-align: justify\">Consistent overstimulation of the thyroid gland that then produces more than normal amounts of thyroid hormone can occur in diseases such as Grave\u2019s disease. Such stimulation may result in an increase in the size of the thyroid gland (= goiter).<\/p>\r\n<p style=\"text-align: justify\">On the other hand, underactivity of the thyroid gland would result in lower amounts of thyroid hormone in the blood. This would decrease the negative feedback effect that thyroid hormone has on the production of TRH from the hypothalamus and TSH from the anterior pituitary. The levels of these compounds in the blood will then rise and stay elevated as long as the level of thyroid hormone remains low. This will continuously stimulate the thyroid gland, causing it to increase in size (= goiter). One of the causes for the inability of the thyroid gland to produce thyroid hormone in the first place is a condition known as <strong>simple goiter<\/strong>, which occurs when the body\u2019s intake of iodine (which is required for the production of thyroid hormone) is not sufficient for its needs.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"797\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image15.jpeg\" alt=\"image\" width=\"797\" height=\"602\" \/> <strong>Figure 11. Goiter.<\/strong> (credit: \u201cAlmazi\u201d\/Wikimedia Commons)[\/caption]\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\"><strong>Calcitonin: <\/strong>The thyroid gland also secretes a hormone called calcitonin that is released in response to a rise in blood calcium levels. It appears to have a function in decreasing blood calcium concentrations by:<\/p>\r\n\r\n<ul style=\"text-align: justify\">\r\n \t<li>Inhibiting the activity of osteoclasts, bone cells that release calcium into the circulation by degrading bone matrix<\/li>\r\n \t<li>Increasing osteoblastic activity (thereby increasing deposition of calcium into bones)<\/li>\r\n \t<li>Decreasing calcium absorption in the intestines<\/li>\r\n \t<li>Increasing calcium loss in the urine<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\">However, these functions are usually not significant in maintaining calcium homeostasis (people with long term increased or decreased calcitonin secretion due to disease usually do not show abnormal blood calcium levels), so the importance of calcitonin is not entirely understood. The production of calcitonin does however respond to levels of calcium in the blood (Figure 13), and pharmaceutical preparations of calcitonin are sometimes prescribed to reduce osteoclast activity in people with osteoporosis and to reduce the degradation of cartilage in people with osteoarthritis.<\/p>\r\n<p style=\"text-align: justify\">Calcium is critical for many biological processes, acting as a second messenger in many signaling pathways, and essential for muscle contraction, nerve impulse transmission, and blood clotting. The necessary tight regulation of blood calcium levels is mainly carried out by the parathyroid glands.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"1-2c\"><\/a>The Parathyroid Glands<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The <strong>parathyroid glands<\/strong> are tiny, round structures usually found embedded in the posterior surface of the thyroid gland (Figure 12). A thick connective tissue capsule separates the glands from the thyroid tissue. Most people have four parathyroid glands. The primary functional cells of the parathyroid glands cells produce and secrete the <strong>parathyroid hormone<\/strong> (<strong>PTH<\/strong>) (also known as parathormone), the major hormone involved in the regulation of blood calcium levels.<\/p>\r\n\r\n\r\n[caption id=\"attachment_38\" align=\"alignnone\" width=\"453\"]<img class=\"wp-image-34 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image5-10-Openstax-posterior-view-thyroid.png\" alt=\"\" width=\"453\" height=\"333\" \/> <strong>Figure 12. Parathyroid Glands.<\/strong> The small parathyroid glands are embedded in the posterior surface of the thyroid gland.[\/caption]\r\n<p style=\"text-align: justify\">The parathyroid glands produce and secrete PTH, a peptide hormone, in response to low blood calcium levels (Figure 13). PTH secretion causes the increase in blood calcium via the following mechanisms:<\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify\">Stimulating the activity of osteoclasts, bone cells that release calcium into the circulation by degrading bone matrix<\/li>\r\n \t<li style=\"text-align: justify\">Inhibiting osteoblastic activity (thereby decreasing deposition of calcium into bones)<\/li>\r\n \t<li style=\"text-align: justify\">Increasing calcium absorption in the intestines by initiating the production of the steroid hormone calcitriol (also known as 1,25-dihydroxyvitamin D), which is the active form of vitamin D3, in the kidneys. Calcitriol then stimulates increased absorption of dietary calcium by the intestines.<\/li>\r\n \t<li style=\"text-align: justify\">Decreasing calcium loss in the urine by causing increased reabsorption of calcium (and magnesium) in the kidney tubules from the urine filtrate<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\">A negative feedback mechanism regulates the levels of PTH, with rising blood calcium levels inhibiting further release of PTH.<\/p>\r\n\r\n\r\n[caption id=\"attachment_38\" align=\"alignnone\" width=\"1186\"]<img class=\"wp-image-35 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/1817_The_Role_of_Parathyroid_Hormone_in_Maintaining_Blood_Calcium_Homeostasis.jpg\" alt=\"\" width=\"1186\" height=\"1425\" \/> <strong>Figure 13. Hormones Involved in Maintaining Blood Calcium Homeostasis.<\/strong> When blood calcium levels drop below the normal range, the release of parathyroid hormone increases and acts to increase calcium levels. When blood calcium levels rise beyond normal levels, the release of calcitonin from the thyroid gland increases and acts to decrease calcium levels.[\/caption]\r\n<h5 style=\"text-align: justify\"><strong><a id=\"1-2d\"><\/a>The Adrenal Glands<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The <strong>adrenal glands<\/strong> are wedges of glandular and neuroendocrine tissue adhering to the top of the kidneys by a fibrous capsule (Figure 14). The adrenal glands have a rich blood supply and experience one of the highest rates of blood flow in the body. The adrenal gland consists of an outer cortex of glandular tissue and an inner medulla of nervous tissue.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1102\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image21.png\" alt=\"image\" width=\"1102\" height=\"316\" \/> <strong>Figure 14. Adrenal Glands.<\/strong> Both adrenal glands sit atop the kidneys and are composed of an outer cortex and an inner medulla, all surrounded by a connective tissue capsule. The cortex can be subdivided into additional zones, all of which produce different types of hormones. LM \u00d7 204. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012). (Knowledge of the zones\u2019 names and responsibility for particular hormone production is not required as examinable material.)[\/caption]\r\n\r\n<strong>Hormones of the adrenal cortex<\/strong>\r\n\r\n<strong>[pb_glossary id=\"411\"]Mineralocorticoids[\/pb_glossary]<\/strong>\r\n<p style=\"text-align: justify\">The most superficial region of the adrenal cortex (zona glomerulosa) produces a group of hormones collectively referred to as <strong>mineralocorticoids<\/strong> because of their effect on body minerals, especially sodium and potassium. These hormones are essential for fluid and electrolyte balance.<\/p>\r\n<p style=\"text-align: justify\"><strong>Aldosterone<\/strong> is the major mineralocorticoid. It is important in the regulation of the concentration of sodium and potassium ions in urine, sweat, and saliva. For example, it is released in response to elevated blood K<sup>+<\/sup>, low blood Na<sup>+<\/sup>, low blood pressure, low blood volume and activation of the renin-angiotensin-aldosterone system (RAAS) (this hormone will be discussed again during the unit dealing with the renal system). In response, aldosterone increases the excretion of K<sup>+<\/sup> and the retention of Na<sup>+<\/sup>, which in turn increases blood volume and blood pressure.<\/p>\r\n<p style=\"text-align: justify\"><strong>[pb_glossary id=\"412\"]Glucocorticoids[\/pb_glossary]<\/strong><\/p>\r\n<p style=\"text-align: justify\">The cells of the middle layer (zona fasciculata) produce hormones called <strong>glucocorticoids<\/strong> because of their role in glucose metabolism. The most important of these is <strong>cortisol<\/strong>. In response to long-term stressors, the hypothalamus secretes CRH, which in turn triggers the release of ACTH by the anterior pituitary. ACTH triggers the release of cortisol. The overall effect is to inhibit tissue building while stimulating the breakdown of stored nutrients to maintain adequate fuel supplies. In conditions of long-term stress, for example, cortisol promotes the catabolism of glycogen to glucose, the catabolism of stored triglycerides into fatty acids and glycerol, and the catabolism of muscle proteins into amino acids. Cortisol increases the body\u2019s resistance to stress by increasing muscle metabolism, maintaining the excitability of nerves and increasing the amount of sugars in the body by promoting <strong>[pb_glossary id=\"396\"]gluconeogenesis[\/pb_glossary]<\/strong>, the conversion of fats and proteins into sugars.<\/p>\r\n<p style=\"text-align: justify\"><strong>Androgens<\/strong><\/p>\r\n<p style=\"text-align: justify\">The innermost layer of the cortex (zona reticularis) produces small amounts of sex hormones called <strong>androgens, <\/strong>which are converted into <strong>testosterone<\/strong> and <strong>estrogens<\/strong> in the tissues. The adrenal cortex serves as the source of sex hormones in an individual until the gonads mature at puberty. The sex hormones of the adrenal cortex play a role in the development of secondary sex characteristics in both males and females. In males, they further increase muscle development. It is interesting to note that the production of the cortical sex hormones is under the influence of adrenocorticotropic hormone from the anterior pituitary gland, and not follicle stimulating hormone or luteinizing hormone.<\/p>\r\n<p style=\"text-align: justify\"><strong>Hormones of the Adrenal Medulla<\/strong><\/p>\r\n<p style=\"text-align: justify\"><strong>Epinephrine and norepinephrine<\/strong> (also sometimes called adrenalin and noradrenalin): These two hormones are both involved in the response to fear, excitement and danger. They both increase blood pressure, and the rate and depth of breathing. Epinephrine, however, increases heart rate and blood sugar levels, whereas norepinephrine reduces the blood flow to the gut and skin.<\/p>\r\n<p style=\"text-align: justify\"><strong>The Stress Response<\/strong><\/p>\r\n<p style=\"text-align: justify\">One of the major functions of the adrenal gland is to respond to stress. Stress can be defined as some occurrence that disrupts homeostasis, and can be either physical or psychological or both. Physical stresses include exposing the body to injury, walking outside in cold and wet conditions without a coat on, or malnutrition. Psychological stresses include the perception of a physical threat, a fight with a loved one, or just a bad day at school.<\/p>\r\n<p style=\"text-align: justify\">The body responds in different ways to short-term stress and long-term stress following a pattern known as the <strong>general adaptation syndrome<\/strong>. The first stage of the general adaptation syndrome is called the\u00a0<strong>alarm reaction<\/strong>. This \u201cfight-or-flight\u201d response, the result of a short-term stressor, is mediated by the hormones epinephrine and norepinephrine from the adrenal medulla, as stimulated by the sympathetic nervous system. Their function is to prepare the body for extreme physical exertion by increasing the heart rate, dilating the airways, and other related responses. Once this stressor is relieved, the body quickly returns to normal.<\/p>\r\n<p style=\"text-align: justify\">If the stressor is not soon relieved, the body attempts to adapt to the stressor in the second stage called the\u00a0<strong>stage of resistance<\/strong>. The primary stress hormone at this stage is cortisol, secreted by the adrenal cortex as a result of signals sent by the hypothalamus and pituitary gland. Cortisol\u2019s effects are widespread. They include the maintenance of blood glucose through synthesizing glucose from compounds such as proteins (gluconeogenesis), and lipolysis so fatty acids can be used for energy by the body, thus preserving glucose. Additionally, the activity of the immune system and inflammation are reduced, as the resources of the body are directed towards dealing with the stress. The physiological adaptations during this stage allow the body to resist the most immediate negative effects of a longer-term stressor.<\/p>\r\n<p style=\"text-align: justify\">However, if the stressor continues for a longer term, the final stage of the stress response may occur. This is known as the\u00a0<strong>stage of exhaustion<\/strong>. At this point, the resources of the body have become depleted and individuals may begin to suffer depression, severe fatigue, or even a fatal heart attack. The continued release of cortisol and other hormones associated with long term stress can cause damage to a variety of organ systems, and this condition has been linked to many diseases such as rheumatoid arthritis, hypertension and gastrointestinal diseases.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"1-2e\"><\/a>The Endocrine Pancreas<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The <strong>pancreas<\/strong> is a long, slender organ, most of which is located posterior to the bottom half of the stomach (Figure 15). Although it is primarily an exocrine gland, secreting a variety of digestive enzymes, the pancreas has an endocrine function. Its<strong> pancreatic islets<\/strong> -\u00a0clusters of cells formerly known as the islets of Langerhans - secrete the hormones glucagon and insulin.<\/p>\r\n<p style=\"text-align: justify\"><strong>Cells and Secretions of the Pancreatic Islets<\/strong><\/p>\r\n<p style=\"text-align: justify\">Cells residing in the pancreatic islets include the following two types of cells.\u00a0 The <strong>alpha cell<\/strong> produces the hormone glucagon and makes up approximately 20 percent of each islet. Glucagon plays an important role in blood glucose regulation; low blood glucose levels stimulate its release.\u00a0The <strong>beta cell<\/strong> produces the hormone insulin and makes up approximately 75 percent of each islet. Elevated blood glucose levels stimulate the release of insulin.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1092\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image22.png\" alt=\"image\" width=\"1092\" height=\"551\" \/> <strong>Figure 15. Pancreas.<\/strong> The pancreatic exocrine function involves the acinar cells secreting digestive enzymes that are transported into the small intestine by the pancreatic duct. Its endocrine function involves the secretion of insulin (produced by beta cells) and glucagon (produced by alpha cells) within the pancreatic islets. These two hormones regulate the rate of glucose metabolism in the body. The micrograph reveals pancreatic islets. LM \u00d7 760. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n<p style=\"text-align: justify\"><strong>Regulation of Blood Glucose Levels by Insulin and Glucagon<\/strong><\/p>\r\n<p style=\"text-align: justify\">Glucose is required for cellular respiration and is the preferred fuel for all body cells. The body derives glucose from the breakdown of the carbohydrate-containing foods and drinks we consume. Glucose not immediately taken up by cells for fuel can be stored by the liver and muscles as glycogen or converted to triglycerides and stored in the adipose tissue. Hormones regulate both the storage and the utilization of glucose as required. Receptors located in the pancreas sense blood glucose levels, and subsequently the pancreatic cells secrete glucagon or insulin to maintain normal levels.<\/p>\r\n<strong>Glucagon: <\/strong>Receptors in the pancreas can sense the decline in blood glucose levels, such as during periods of fasting or during prolonged labour or exercise (Figure 16). In response, the alpha cells of the pancreas secrete the hormone <strong>glucagon<\/strong>, which has several effects:\r\n<ul>\r\n \t<li style=\"text-align: justify\">It stimulates the liver to perform <strong>[pb_glossary id=\"414\"]glycogenolysis[\/pb_glossary]<\/strong>, the breaking down of glycogen into its component glucose building blocks. The resulting glucose is then released into the circulation for use by body cells.<\/li>\r\n \t<li style=\"text-align: justify\">It stimulates gluconeogenesis in the liver, converting amino acids from body proteins into glucose.<\/li>\r\n \t<li style=\"text-align: justify\">It stimulates lipolysis, the breakdown of stored triglycerides into free fatty acids and glycerol. Some of the free glycerol released into the bloodstream travels to the liver, which converts it into glucose. This is also a form of gluconeogenesis.<\/li>\r\n<\/ul>\r\n<p style=\"text-align: justify\">Taken together, these actions increase blood glucose levels. The activity of glucagon is regulated through a negative feedback mechanism; rising blood glucose levels inhibit further glucagon production and secretion.<\/p>\r\n<p style=\"text-align: justify\"><strong>Insulin: <\/strong>The primary function of <strong>insulin <\/strong>is to facilitate the uptake of glucose into body cells. Red blood cells, as well as cells of the brain, kidneys, and the lining of the small intestine, do not have insulin receptors on their cell membranes and do not require insulin for glucose uptake. Although all other body cells do require insulin if they are to take glucose from the bloodstream, skeletal muscle cells and adipose cells are the primary targets of insulin.<\/p>\r\n<p style=\"text-align: justify\">Insulin also reduces blood glucose levels by stimulating glycolysis, the metabolism of glucose for generation of ATP. Moreover, it stimulates the liver to perform <strong>[pb_glossary id=\"415\"]glycogenesis[\/pb_glossary]<\/strong>, converting excess glucose into glycogen for storage, and it inhibits enzymes involved in glycogenolysis and gluconeogenesis. Finally, insulin promotes triglyceride and protein synthesis. The secretion of insulin is regulated through a negative feedback mechanism. As blood glucose levels decrease, further insulin release is inhibited.<\/p>\r\n<p style=\"text-align: justify\"><strong>Hormonal Control of Blood Glucose: <\/strong>The hormonal control of blood glucose\u00a0is\u00a0more\u00a0complex than\u00a0just\u00a0the interaction between insulin and glucagon.\u00a0 Along with glucagon, the\u00a0following\u00a0hormones are called \u201ccounterregulatory\u201d hormones, because\u00a0their effects on glucose levels\u00a0are opposite to\u00a0that of insulin, i.e.,\u00a0they\u00a0all act\u00a0to\u00a0increase\u00a0the level of glucose in the blood:<\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify\"><strong>Epinephrine<\/strong> stimulates the breakdown of glycogen in the liver and muscle (glycogenolysis)<\/li>\r\n \t<li style=\"text-align: justify\"><strong>Growth hormone<\/strong>\u00a0stimulates the mobilization and breakdown of fats,\u00a0and decreases\u00a0the uptake of glucose by fat cells<\/li>\r\n \t<li style=\"text-align: justify\"><strong>Cortisol\u00a0<\/strong>stimulates the breakdown of proteins and their use in the production of glucose (gluconeogenesis)<\/li>\r\n<\/ul>\r\n[caption id=\"\" align=\"alignnone\" width=\"610\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image23.png\" alt=\"image\" width=\"610\" height=\"855\" \/> <strong>Figure 16. Homeostatic Regulation of Blood Glucose Levels.<\/strong> Blood glucose concentration is tightly maintained between 70 mg\/dL and 110 mg\/dL. If blood glucose concentration rises above this range, insulin is released, which stimulates body cells to remove glucose from the blood. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood.[\/caption]\r\n\r\n&nbsp;\r\n<h5 style=\"text-align: justify\"><strong><a id=\"1-2f\"><\/a>The endocrine functions of the ovaries and testes<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The <strong>ovaries<\/strong> produce two hormones: estrogens and progesterone. <strong>Estrogens<\/strong> are produced by ovarian follicles. Estrogens stimulate the growth of both primary and secondary sex characteristics. Primary sex characteristics in the female include the growth of the uterus and vagina, and the secondary characteristics include the development of body hair, enlarged breasts and a wider pelvis.<\/p>\r\n<p style=\"text-align: justify\"><strong>Progesterone<\/strong> is produced by the corpus luteum. It stimulates the development of milk-secretory tissue in the breasts, prepares the uterine lining for the implantation of a fertilized oocyte, and helps to maintain pregnancy.<\/p>\r\n<p style=\"text-align: justify\">The <strong>testes<\/strong> in the male produce the hormone <strong>testosterone<\/strong>. This hormone stimulates the development of primary sex characteristics, such as the accessory glands and the penis, and secondary sex characteristics such as body hair and a deepening of the voice.<\/p>\r\n\r\n<h5><strong><a id=\"1-2g\"><\/a>The endocrine functions of the stomach and the duodenum<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The principal function of the <strong>stomach <\/strong>is, of course, digestion. We are most familiar with the capacity of the stomach to store food, and its role in the mechanical and chemical digestion of food. However, there is also some endocrine tissue in the stomach. The secretion of hydrochloric acid in the stomach, and some enzymes, is under the control of a hormone called <strong>gastrin<\/strong>, which is produced by glandular tissue in the wall of the stomach. This hormone is produced by the stomach, travels through the bloodstream, and stimulates the exocrine tissue of the stomach.<\/p>\r\n<p style=\"text-align: justify\">The <strong>[pb_glossary id=\"416\"]duodenum [\/pb_glossary] <\/strong>also has glandular tissue in its walls. One of the hormones it produces is called <strong>secretin. <\/strong>Secretin travels through the blood and stimulates the pancreas to produce pancreatic juice, which then enters the duodenum and aids in digestion.<\/p>\r\n\r\n<h5><strong><a id=\"1-2h\"><\/a>Thymus and the pineal gland<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The <strong>thymus gland <\/strong>was once thought to be a [pb_glossary id=\"417\"]vestigial [\/pb_glossary] organ. However, it has been determined that it is a central gland of the lymphatic system, which is involved in the body\u2019s immune system. As part of this activity, the gland produces a hormone called <strong>thymosin<\/strong>, which is involved in the maturation and development of the immune system. This gland is larger in infants and decreases in size through adulthood. As a result of the change in size of the gland, the amounts of thymosin produced similarly decrease throughout adulthood.<\/p>\r\n<p style=\"text-align: justify\">The <strong>pineal gland<\/strong>, situated in the brain, produces the hormone <strong>melatonin<\/strong>. The pineal gland is an interesting structure, because it is responsive to light and may be involved in the seasonal behaviour changes by some animals in response to changes in day length. This hormone also acts on the hypothalamus inhibiting the release of luteinizing hormone, thus affecting the activity of the gonads.<\/p>\r\n\r\n<h5><strong><a id=\"1-2i\"><\/a>Special nature of the prostaglandins<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Prostaglandins are lipids, much like some hormones. However, they are not produced in special organs or glands, but rather by many cell types from lipids in their own plasma membranes. They usually do not travel long distances within the body, but typically have effects on the tissue where they are produced.<\/p>\r\n<p style=\"text-align: justify\">The effects of prostaglandins are numerous, including the regulation of blood pressure, regulation of stomach secretions, stimulation and inhibition of uterine contractions, and the transmission of nerve impulses. At least 15 different prostaglandins have been discovered so far. They are vital for the normal functioning of the body. Prostaglandins were originally discovered in the secretions of the prostate gland, from which they got their name.<\/p>\r\n\r\n<h2><a id=\"1-3\"><\/a>Part 3: Summary of Glands, Hormones, their Stimuli, Targets, and Effects<\/h2>\r\n<table style=\"border-collapse: collapse;width: 100%;height: 1105px\" border=\"0\"><caption>Table 3: Summary of Glands, Hormones, their Stimuli, Targets, and Effects.<\/caption>\r\n<thead>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><strong>Organ\/Gland<\/strong><\/td>\r\n<td style=\"width: 9.97641%;height: 15px\"><strong>Hormone<\/strong><\/td>\r\n<td style=\"width: 24.2578%;height: 15px\"><strong>Stimuli<\/strong><\/td>\r\n<td style=\"width: 18.0824%;height: 15px\"><strong>Target<\/strong><\/td>\r\n<td style=\"width: 19.112%;height: 15px\"><strong>Function\/Effects<\/strong><\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>Disorders<\/strong><\/td>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\">Hypothalamus<\/td>\r\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">[Adreno]corticotropic Releasing Hormone (ACTHRH\/CRH)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Nervous impulse<\/li>\r\n \t<li><span style=\"font-family: inherit;font-size: inherit\">Cortisol (negative feedback mechanism)<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\r\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Adrenocorticotropic hormone (ACTH)<\/td>\r\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Adrenal glands<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Thyroid stimulating hormone releasing\u00a0 hormone (TRH)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Nervous impulse<\/li>\r\n \t<li><span style=\"font-family: inherit;font-size: inherit\">Thyroxin (negative feedback mechanism)<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\r\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Thyroid Stimulating hormone (TSH)<\/td>\r\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Thyroid glands<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Gonadotropin releasing hormone (GnRH)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Nervous impulse<\/li>\r\n \t<li>Testosterone\/Estrogens (negative feedback <span style=\"font-family: inherit;font-size: inherit\">mechanism<\/span>)<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\r\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Luteinizing hormone\r\n\r\n\u21d1 Follicle Stimulating hormone (FSH)<\/td>\r\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Ovaries and Testes<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Growth hormone releasing hormone (GHRH)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Nervous impulse<\/li>\r\n \t<li><span style=\"font-family: inherit;font-size: inherit\">Growth hormone (negative feedback mechanism)<\/span><\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\r\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Growth hormone (GH)<\/td>\r\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Pituitary<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Prolactin releasing hormone (PRH)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Nervous impulse<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\r\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Prolactin (PRL)<\/td>\r\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Pituitary<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Prolactin inhibiting hormone (PIH)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Nervous impulse<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\r\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d3 Prolactin (PRL)<\/td>\r\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Pituitary<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Oxytocin\r\n\r\n<em><span style=\"font-family: inherit;font-size: inherit\">(produced by the hypothalamus and released from the posterior pituitary)<\/span><\/em><\/td>\r\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">Nervous impulse in response to cervical\/uterine stretching<\/td>\r\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Uterus<\/li>\r\n \t<li>Breast<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">Target\u00a0 uterus:\r\n<ul>\r\n \t<li>Contraction of the uterus during childbirth<\/li>\r\n \t<li>Induce labor<\/li>\r\n<\/ul>\r\nTarget breast:\r\n<ul>\r\n \t<li>Release of milk during breastfeeding<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">Unknown<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Antidiuretic hormone\r\n\r\n<em style=\"font-family: inherit;font-size: inherit\">(produced by the hypothalamus and released from the posterior pituitary)<\/em><\/td>\r\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">Nervous impulse in response to \u21d1 blood osmolarity or \u21d3<span style=\"font-family: inherit;font-size: inherit\">\u00a0blood volume<\/span><\/td>\r\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Kidney (DCT, Collecting duct)<\/td>\r\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 water reabsorption<\/td>\r\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\"><strong>Hyposecretion<\/strong>: Diabetes insipidus\r\n\r\n<strong>Hypersecretion<\/strong>: Syndrome of inappropriate ADH secretion<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\">Pituitary gland [Hypophysis]<\/td>\r\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Adrenocorticotropic hormone (ACTH)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">ACTHRH\/CRH<\/td>\r\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Adrenal glands<\/td>\r\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 cortisol\r\n\r\n\u21d1 testosterone\r\n\r\n\u21d1 aldosterone<\/td>\r\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Adrenal glands<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Thyroid Stimulating hormone (TSH)<\/td>\r\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">TRH<\/td>\r\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: middle\">Thyroid gland<\/td>\r\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">\u21d1 Thyroxin<\/td>\r\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\">see Thyroid gland<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Luteinizing hormone (LH)<\/td>\r\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">GnRH<\/td>\r\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Ovaries<\/li>\r\n \t<li>Testes<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">Target ovaries:\r\n<ul>\r\n \t<li>\u21d1 Estrogens<\/li>\r\n \t<li>\u21d1 Progesterone<\/li>\r\n<\/ul>\r\nTarget testes:\r\n<ul>\r\n \t<li>\u21d1 testosterone<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\">see Ovaries and Testes<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Follicle Stimulating hormone (FSH)<\/td>\r\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">GnRH<\/td>\r\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Ovaries<\/li>\r\n \t<li>Testes<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">Target ovaries:\r\n<ul>\r\n \t<li>\u21d1 Estrogens<\/li>\r\n \t<li>\u21d1 Progesterone<\/li>\r\n<\/ul>\r\nTarget testes:\r\n<ul>\r\n \t<li>\u21d1 testosterone<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\">see Ovaries and Testes<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Growth hormone (GH)<\/td>\r\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">GHRH<\/td>\r\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: middle\">Liver, muscle, cartilage, bones, several other organs<\/td>\r\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">\r\n<ul>\r\n \t<li>Growth<\/li>\r\n \t<li>\u21d1 protein synthesis<\/li>\r\n \t<li>\u21d1 breakdown of fats<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\"><strong>Hyposecretion: <\/strong>\r\n<ul>\r\n \t<li>Dwarfism in children<\/li>\r\n \t<li>Simmond\u2019s disease in adults<\/li>\r\n<\/ul>\r\n<strong>Hypersecretion:<\/strong>\r\n<ul>\r\n \t<li>Gigantism in children<\/li>\r\n \t<li>Acromegaly in adults<\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Prolactin (PRL)<\/td>\r\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">Prolactin releasing hormone (PRH)<\/td>\r\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: top\">Mammary glands<\/td>\r\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">\u21d1 milk production<\/td>\r\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\">Unknown<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 10.1674%;height: 29px\">Thyroid<\/td>\r\n<td style=\"width: 9.97641%;height: 29px\">Thyroid hormones<\/td>\r\n<td style=\"width: 24.2578%;height: 29px\">TSH<\/td>\r\n<td style=\"width: 18.0824%;height: 29px\">Most cells<\/td>\r\n<td style=\"width: 19.112%;height: 29px\">\r\n<ul>\r\n \t<li>\u21d1 protein synthesis<\/li>\r\n \t<li>\u21d1 breakdown of fats<\/li>\r\n \t<li>\u21d1 breakdown of carbs<\/li>\r\n \t<li>\u21d1 synthesis of Na+\/K+ pumps<\/li>\r\n \t<li>regulates the development of nervous &amp; skeletal systems<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 29px\"><strong>Hyposecretion<\/strong>\r\n<ul>\r\n \t<li>Cretinism in children<\/li>\r\n \t<li>Myxedema in adults<\/li>\r\n<\/ul>\r\n<strong>Hypersecretion<\/strong>\r\n<ul>\r\n \t<li>Grave\u2019s disease<\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 29px\">Calcitonin<\/td>\r\n<td style=\"width: 24.2578%;height: 29px\">\u21d1 Ca<sup>2+<\/sup> levels<\/td>\r\n<td style=\"width: 18.0824%;height: 29px\">Skeleton cells (osteoclasts)<\/td>\r\n<td style=\"width: 19.112%;height: 29px\">\u21d3 blood Ca<sup>2+<\/sup> levels by inhibiting bone resorption and the release of Ca<sup>2+<\/sup> and stimulating Ca<sup>2+<\/sup> uptake and incorporation into the bone matrix<\/td>\r\n<td style=\"width: 18.4042%;height: 29px\">Very rare<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 10.1674%;height: 29px\">Parathyroid<\/td>\r\n<td style=\"width: 9.97641%;height: 29px\">Parathyroid hormone<\/td>\r\n<td style=\"width: 24.2578%;height: 29px\">\u21d3 Ca<sup>2+<\/sup> levels<\/td>\r\n<td style=\"width: 18.0824%;height: 29px\">Skeleton cells (osteoclasts), kidney and intestine<\/td>\r\n<td style=\"width: 19.112%;height: 29px\">\u21d1 blood Ca<sup>2+<\/sup> levels<\/td>\r\n<td style=\"width: 18.4042%;height: 29px\"><strong>Hyposecretion<\/strong>\r\n<ul>\r\n \t<li>Spams, convulsions<\/li>\r\n<\/ul>\r\n<strong>Hypersecretion<\/strong>\r\n<ul>\r\n \t<li>\u21d1 Bone softness, weaken skeletal muscles<\/li>\r\n \t<li>\u21d1 Kidney stones<\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n<tr style=\"height: 171px\">\r\n<td style=\"width: 10.1674%;height: 171px\">Adrenal glands<\/td>\r\n<td style=\"width: 9.97641%;height: 171px\">Aldosterone\r\n\r\n<em>(type of mineralocorticoid)<\/em><\/td>\r\n<td style=\"width: 24.2578%;height: 171px\">\r\n<ul>\r\n \t<li>\u21d3 blood pressure<\/li>\r\n \t<li>\u21d3 Na+<\/li>\r\n \t<li>\u21d1 K+<\/li>\r\n \t<li>\u21d1 renin-angiotensin<\/li>\r\n \t<li>\u21d1 ACTH<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 171px\">Kidney cells<\/td>\r\n<td style=\"width: 19.112%;height: 171px\">\u21d1 Na<sup>+<\/sup> reabsorption\r\n\r\n\u21d1 excretion of K<sup>+<\/sup>, H<sup>+<\/sup><\/td>\r\n<td style=\"width: 18.4042%;height: 171px\"><strong>Hyposecretion<\/strong>\r\n<ul>\r\n \t<li>Addison\u2019s disease<\/li>\r\n<\/ul>\r\n<strong>Hypersecretion<\/strong>\r\n<ul>\r\n \t<li>Aldosteronism<\/li>\r\n<\/ul>\r\n<strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 156px\">\r\n<td style=\"width: 10.1674%;height: 156px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 156px\">Cortisol\r\n\r\n<em>(type of glucocorticoid)<\/em><\/td>\r\n<td style=\"width: 24.2578%;height: 156px\">\r\n<ul>\r\n \t<li>\u21d3 ACTH<\/li>\r\n \t<li>Stress<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 156px\">Most body cells<\/td>\r\n<td style=\"width: 19.112%;height: 156px\">\u21d1 Muscle metabolism\r\n\r\n\u21d1 glucose blood levels\r\n\r\n\u21d1 blood pressure (vasoconstriction)<\/td>\r\n<td style=\"width: 18.4042%;height: 156px\"><strong>Hyposecretion<\/strong>\r\n<ul>\r\n \t<li>Addison\u2019s disease<\/li>\r\n<\/ul>\r\n<strong>Hypersecretion<\/strong>\r\n<ul>\r\n \t<li>Cushing\u2019s disease<strong>\r\n<\/strong><\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 10.1674%;height: 32px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 32px\">Testosterone <em>(in small amounts)<\/em><\/td>\r\n<td style=\"width: 24.2578%;height: 32px\"><\/td>\r\n<td style=\"width: 18.0824%;height: 32px\">Various body cells<\/td>\r\n<td style=\"width: 19.112%;height: 32px\">Development of secondary sex characteristics<\/td>\r\n<td style=\"width: 18.4042%;height: 32px\"><strong>Hypersecretion<\/strong>\r\n<ul>\r\n \t<li>Masculinization of females<\/li>\r\n<\/ul>\r\n<\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px\">Epinephrine (adrenaline)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px\">Stress<\/td>\r\n<td style=\"width: 18.0824%;height: 15px\">Many body cells<\/td>\r\n<td style=\"width: 19.112%;height: 15px\">\r\n<ul>\r\n \t<li>\u21d1 blood pressure (vasoconstriction)<\/li>\r\n \t<li>\u21d1 blood flow to heart and muscles<\/li>\r\n \t<li>\u21d1 bronchial dilatation<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px\">Norepinephrine (noradrenaline)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px\">Stress<\/td>\r\n<td style=\"width: 18.0824%;height: 15px\">Many body cells<\/td>\r\n<td style=\"width: 19.112%;height: 15px\">\r\n<ul>\r\n \t<li>\u21d1 blood pressure (vasoconstriction)<\/li>\r\n \t<li>\u21d3 blood flow to gut &amp; skins<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px\">Estrogens<\/td>\r\n<td style=\"width: 24.2578%;height: 15px\">\r\n<ul>\r\n \t<li>Luteinizing hormone (LH)<\/li>\r\n \t<li>Follicle Stimulating hormone (FSH)<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px\">\r\n<ul>\r\n \t<li>Uterus<\/li>\r\n \t<li>Vagina<\/li>\r\n \t<li>Several body cells<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 19.112%;height: 15px\">Development of primary and secondary sex characteristics (body hair, breasts, pelvis)<\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 15px\">Progesterone<\/td>\r\n<td style=\"width: 24.2578%;height: 15px\">\r\n<ul>\r\n \t<li>Luteinizing hormone (LH)<\/li>\r\n \t<li>Follicle Stimulating hormone (FSH)<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px\">\r\n<ul>\r\n \t<li>Uterus<\/li>\r\n \t<li>Vagina<\/li>\r\n \t<li>Several body cells<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 19.112%;height: 15px\">Development of primary and secondary sex characteristics (body hair, breasts, pelvis)<\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\">Testis<\/td>\r\n<td style=\"width: 9.97641%;height: 15px\">Testosterone<\/td>\r\n<td style=\"width: 24.2578%;height: 15px\">\r\n<ul>\r\n \t<li>Luteinizing hormone (LH)<\/li>\r\n \t<li>Follicle Stimulating hormone (FSH)<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px\">\r\n<ul>\r\n \t<li>Penis<\/li>\r\n \t<li>Several body cells<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 19.112%;height: 15px\">Development of primary and secondary sex characteristics (body hair, voice change)<\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\">Thymus<\/td>\r\n<td style=\"width: 9.97641%;height: 15px\">Thymosin<\/td>\r\n<td style=\"width: 24.2578%;height: 15px\">\r\n<ul>\r\n \t<li>Prolactin<\/li>\r\n \t<li>Thyroid<\/li>\r\n \t<li>Adrenal hormones<\/li>\r\n \t<li>Gonads<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.0824%;height: 15px\">Immune system<\/td>\r\n<td style=\"width: 19.112%;height: 15px\">Development of the immune system<\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\">Pineal gland<\/td>\r\n<td style=\"width: 9.97641%;height: 15px\">Melatonin<\/td>\r\n<td style=\"width: 24.2578%;height: 15px\">Light<\/td>\r\n<td style=\"width: 18.0824%;height: 15px\">Hypothalamus<\/td>\r\n<td style=\"width: 19.112%;height: 15px\">Regulation of daily circadian rhythm<\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\">Body Tissues<\/td>\r\n<td style=\"width: 9.97641%;height: 15px\">Prostaglandins<\/td>\r\n<td style=\"width: 24.2578%;height: 15px\">\u2018Local homeostatic imbalance\u2019<\/td>\r\n<td style=\"width: 18.0824%;height: 15px\">Several body cells<\/td>\r\n<td style=\"width: 19.112%;height: 15px\">\r\n<ul>\r\n \t<li>Regulation of blood pressure<\/li>\r\n \t<li>Stomach secretions<\/li>\r\n \t<li>Immune response<\/li>\r\n \t<li>Clotting<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 15px\">\r\n<td style=\"width: 10.1674%;height: 15px\">Pancreas (Islets of Langerhans)<\/td>\r\n<td style=\"width: 9.97641%;height: 15px\">Glucagon (alpha cells)<\/td>\r\n<td style=\"width: 24.2578%;height: 15px\">\u21d3 Blood glucose levels<\/td>\r\n<td style=\"width: 18.0824%;height: 15px\">Liver and other organs\/tissues<\/td>\r\n<td style=\"width: 19.112%;height: 15px\">\u21d1 Blood glucose levels by:\r\n<ul>\r\n \t<li>\u21d1 gluconeogenesis,<\/li>\r\n \t<li>\u21d1 glycogen breakdown,<\/li>\r\n \t<li>\u21d1 triglycerides breakdown<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\r\n<\/tr>\r\n<tr style=\"height: 171px\">\r\n<td style=\"width: 10.1674%;height: 171px\"><\/td>\r\n<td style=\"width: 9.97641%;height: 171px\">Insulin (beta cells)<\/td>\r\n<td style=\"width: 24.2578%;height: 171px\">\u21d1 Blood glucose levels<\/td>\r\n<td style=\"width: 18.0824%;height: 171px\">Liver and other organs\/tissues<\/td>\r\n<td style=\"width: 19.112%;height: 171px\">\u21d3 Blood glucose levels by:\r\n<ul>\r\n \t<li>\u21d1 cell glucose uptake,<\/li>\r\n \t<li>\u21d1 glycogen synthesis,<\/li>\r\n \t<li>\u21d1 fatty acid synthesis<\/li>\r\n<\/ul>\r\n<\/td>\r\n<td style=\"width: 18.4042%;height: 171px\"><strong>Hyposecretion<\/strong>\r\n<ul>\r\n \t<li>Diabetes mellitus<\/li>\r\n<\/ul>\r\n<strong>Hypersecretion<\/strong>\r\n<ul>\r\n \t<li>Hyperinsulinism<\/li>\r\n<\/ul>\r\n&nbsp;<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<div class=\"textbox textbox--exercises\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><a id=\"P\"><\/a>Practice Questions<\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<p style=\"text-align: justify\"><strong>Part 1:<\/strong> General properties of the endocrine system<\/p>\r\n[h5p id=\"72\"]\r\n\r\n<strong>Part 2:<\/strong> Major endocrine organs and their secretions\r\n\r\n[h5p id=\"73\"]\r\n\r\n[h5p id=\"74\"]\r\n\r\n[h5p id=\"75\"]\r\n\r\n[h5p id=\"76\"]\r\n\r\n[h5p id=\"77\"]\r\n\r\n[h5p id=\"78\"]\r\n\r\n[h5p id=\"79\"]\r\n\r\n[h5p id=\"80\"]\r\n\r\n<\/div>\r\n<\/div>\r\n&nbsp;","rendered":"<div class=\"textbox shaded\">\n<p style=\"text-align: justify\"><strong>Unit Outline<\/strong><\/p>\n<p style=\"text-align: justify\"><a href=\"#1\"><strong>Part 1:<\/strong> General properties of the endocrine system<\/a><\/p>\n<ul>\n<li><a href=\"#1-1a\">Introduction: the two general categories of glands in the body<\/a><\/li>\n<li><a href=\"#1-1b\">General functions of hormones<\/a><\/li>\n<li><a href=\"#1-1c\">Hormone secretion: regulation and stimuli<\/a><\/li>\n<li><a href=\"#1-1d\">Types of hormones<\/a><\/li>\n<li><a href=\"#1-1e\">Pathways of hormone action<\/a><\/li>\n<li><a href=\"#1-1f\">Comparison of Endocrine and Nervous systems<\/a><\/li>\n<\/ul>\n<p style=\"text-align: justify\"><a href=\"#2\"><strong>Part 2:<\/strong> Major endocrine organs and their secretions<\/a><\/p>\n<ul>\n<li><a href=\"#1-2a\">Hypothalamus and pituitary glands<\/a><\/li>\n<li><a href=\"#1-2b\">Thyroid gland<\/a><\/li>\n<li><a href=\"#1-2c\">Parathyroid gland<\/a><\/li>\n<li><a href=\"#1-2d\">The adrenal glands<\/a><\/li>\n<li><a href=\"#1-2e\">The endocrine pancreas<\/a><\/li>\n<li><a href=\"#1-2f\">Endocrine functions of the ovaries and testes<\/a><\/li>\n<li><a href=\"#1-2g\">Endocrine functions of the stomach and duodenum<\/a><\/li>\n<li><a href=\"#1-2h\">Thymus and pineal gland<\/a><\/li>\n<li><a href=\"#1-2i\">The special nature of prostaglandins<\/a><\/li>\n<\/ul>\n<p><a href=\"#1-3\"><strong>Part 3:<\/strong> Summary of Glands, Hormones, their Stimuli, Targets and Effects<\/a><\/p>\n<h2><a href=\"#P\">Practice Questions<\/a><\/h2>\n<\/div>\n<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><strong>Learning Objectives<\/strong><\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p>At the end of this unit, you should be able to:<\/p>\n<p class=\"hanging-indent\"><strong>I.<\/strong> Define \u201cgland\u201d.<\/p>\n<p class=\"hanging-indent\"><strong>II.<\/strong> Distinguish between endocrine glands and exocrine glands.<\/p>\n<p class=\"hanging-indent\"><strong>III.<\/strong> Describe the purpose and regulation of hormone secretion.<\/p>\n<p class=\"hanging-indent\"><strong>IV.<\/strong> Describe stimuli for hormone secretion.<\/p>\n<p class=\"hanging-indent\"><strong>V.<\/strong> Describe the main categories of hormones, and how this relates to their receptors and signaling pathways.<\/p>\n<p class=\"hanging-indent\"><strong>VI.<\/strong> Compare and contrast the nervous and endocrine systems.<\/p>\n<p class=\"hanging-indent\"><strong>VII.<\/strong> Identify on a diagram of the human body the locations of important endocrine glands.<\/p>\n<p class=\"hanging-indent\"><strong>VIII.<\/strong> Describe the hypothalamus and pituitary glands and their interrelationship.<\/p>\n<p><strong>IX.<\/strong> Describe the function and secretion of hormones released by the pituitary gland.<\/p>\n<p><strong>X.<\/strong> Describe the function and secretion of hormones released by the thyroid gland.<\/p>\n<p class=\"hanging-indent\"><strong>XI.<\/strong> Describe the function and secretion of hormones released by the parathyroid glands.<\/p>\n<p class=\"hanging-indent\"><strong>XII.<\/strong> Describe the function and secretion of hormones released by the adrenal gland.<\/p>\n<p class=\"hanging-indent\"><strong>XIII.<\/strong> Describe the function and secretion of hormones released by the pancreas.<\/p>\n<p class=\"hanging-indent\"><strong>XIV.<\/strong> Name the hormones produced by the following glands and describe their actions: ovaries, testes, stomach, duodenum, thymus and pineal gland.<\/p>\n<p class=\"hanging-indent\"><strong>XV.<\/strong> Describe prostaglandins, referring to their composition, where they are produced, where they generally have an effect, and four effects.<\/p>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><strong>Learning Objectives and Guiding Questions<\/strong><\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p>At the end of this unit, you should be able to complete all the following tasks, including answering the guiding questions associated with each task.<\/p>\n<p class=\"hanging-indent\"><strong>I.<\/strong> Define \u201cgland\u201d.<\/p>\n<p class=\"hanging-indent\"><strong>II.<\/strong> Distinguish between endocrine glands and exocrine glands.<\/p>\n<ol>\n<li>Describe the different means by which exocrine and endocrine glands release their secretions.<\/li>\n<li>Identify the general difference between the types of secretions that these two types of glands secrete and name two examples of secretions from each type of gland.<\/li>\n<li>Name two organs in the body that have both exocrine and endocrine functions. Identify the exocrine and endocrine secretions of one of these organs.<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>III.<\/strong> Describe the purpose and regulation of hormone secretion.<\/p>\n<ol>\n<li>Specify the fundamental function of the endocrine system (include the definition of homeostasis).<\/li>\n<li>Describe six overall functions of hormones.<\/li>\n<li>Name and describe the type of feedback <span style=\"font-family: inherit;font-size: inherit\">mechanism <\/span>that is most commonly involved in hormone regulation. Identify the &#8220;output&#8221; of this feedback <span style=\"font-family: inherit;font-size: inherit\">mechanism<\/span>.<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>IV.<\/strong> Describe stimuli for hormone secretion.<\/p>\n<ol>\n<li>Compare and contrast the three stimuli for hormone release: humoral, hormonal and nervous<\/li>\n<li>Describe three examples of hormones that have humoral stimuli.\n<ul>\n<li>Name the hormone, the organ that releases the hormone and the compound which is controlled by the hormone.<\/li>\n<li>Identify whether these are positive or negative feedback mechanisms.<\/li>\n<\/ul>\n<\/li>\n<li>Describe one example of a hormone that is controlled by levels of other hormone(s).\n<ul>\n<li>Name the hormone and the organ that releases it.<\/li>\n<li>Name the organs that release hormones that control the release of this hormone<\/li>\n<li>Describe how the levels of the first hormone and those of the controlling hormones are related to each other<\/li>\n<li>Identify whether this is a positive or negative feedback mechanism.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>V.<\/strong> Describe the main categories of hormones, and how this relates to their receptors and signaling pathways.<\/p>\n<ol>\n<li>Explain the basis upon which hormones are divided into two major groups.<\/li>\n<li>Name and describe the three types of hormones.\n<ul>\n<li>Identify from which compounds each type is derived.<\/li>\n<li>Name two examples of each type and actions of each example.<\/li>\n<li>Identify which type of hormone has the longest half-life and explain the reason for this difference.<\/li>\n<\/ul>\n<\/li>\n<li>Explain why, although they circulate throughout the body, hormones are able to target specific cells.<\/li>\n<li>Name five responses that may occur when a hormone successfully interacts with a cell.<\/li>\n<li>Distinguish between intracellular and extracellular receptors\n<ul>\n<li>For each type of receptor, identify the location (inside or on the cell membrane), and the type of hormone with which they interact (i.e., whether lipid or amino acid based).<\/li>\n<li>Explain why the type of receptor used by a particular hormone is related to the hydrophilic nature of the hormone.<\/li>\n<li>Give two examples of hormones that interact with each of the two types of receptor.<\/li>\n<li>Distinguish between the general mechanism that occurs after hormones interact with each of the two types of receptors.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>VI.<\/strong> Compare and contrast the nervous and endocrine systems.<\/p>\n<ol>\n<li>Identify the type of intercellular communication each system uses.<\/li>\n<li>Describe the anatomical relationship between the sending and receiving cells in each system.<\/li>\n<li>Identify which system has the more rapid and specific method of message transmission and explain the reason for this.<\/li>\n<li>Differentiate between the general purposes of the two systems (i.e., which type of body function is mainly governed by each type).<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>VII.<\/strong> Identify on a diagram of the human body the locations of each of the following glands (or parts of glands):<\/p>\n<ol>\n<li>Pineal gland<\/li>\n<li>Thymus<\/li>\n<li>Hypothalamus<\/li>\n<li>Adrenal glands<\/li>\n<li>Adrenal cortex<\/li>\n<li>Adrenal medulla<\/li>\n<li>Anterior pituitary<\/li>\n<li>Posterior pituitary<\/li>\n<li>Pancreatic islets<\/li>\n<li>Thyroid<\/li>\n<li>Ovaries<\/li>\n<li>Testes<\/li>\n<li>Parathyroid glands<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>VIII.<\/strong> Describe the hypothalamus and pituitary glands and their interrelationship.<\/p>\n<ol>\n<li>Justify the basis for labelling the hypothalamus-pituitary complex as the \u201ccommand centre\u201d of the endocrine system.<\/li>\n<li>Describe (or draw) the location of the hypothalamus and the anterior pituitary gland, and the anatomical connection between the two glands, including the nature of the vascular connection.<\/li>\n<li>Describe how a signal is sent from the hypothalamus to the anterior pituitary, to either inhibit or stimulate the release of an anterior pituitary hormone.<\/li>\n<li>Name and describe the functions of six hypothalamic hormones that control the secretions of the anterior pituitary.<\/li>\n<li>Describe (or draw) the location of the hypothalamus and the posterior pituitary gland, and the anatomical connection between the two glands, including the nature of the neural connection.<\/li>\n<li>Name the two hypothalamic hormones that are stored in and secreted from the posterior pituitary.<\/li>\n<\/ol>\n<p><strong>IX.<\/strong> Describe the function and secretion of hormones released by the pituitary gland.<\/p>\n<ol>\n<li>Explain what is meant by four of the anterior pituitary hormones being referred to as \u201ctropic\u201d hormones.<\/li>\n<li>Name and describe the functions of the two anterior pituitary hormones that do not control the secretion of other endocrine glands.<\/li>\n<li>Describe how the levels of these hormones are controlled.<\/li>\n<li>Name and describe the actions of the four tropic hormones released by the anterior pituitary.<\/li>\n<li>Describe where the hormones that the posterior pituitary secretes are actually produced, and how they are transported to the posterior pituitary.<\/li>\n<li>Name and describe the actions of the two hormones released by the posterior pituitary.<\/li>\n<li>Describe how the levels of these hormones are controlled.<\/li>\n<\/ol>\n<p><strong>X.<\/strong> Describe the function and secretion of hormones released by the thyroid gland.<\/p>\n<ol>\n<li>Describe the location of the thyroid gland.<\/li>\n<li>Name the two hormones released by the thyroid gland.<\/li>\n<li>Describe the stimulus for, and control of, the release of thyroid hormone.<\/li>\n<li>Name the two compounds that are grouped under the term \u201cthyroid hormone\u201d.<\/li>\n<li>Name and define the bodily process that is increased by the release of thyroid hormone.<\/li>\n<li>State four other processes for which thyroid hormone is required.<\/li>\n<li>Describe the stimulus for, control and action of, calcitonin. Identify the type of feedback mechanism involved.<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>XI.<\/strong> Describe the function and secretion of hormones released by the parathyroid glands.<\/p>\n<ol>\n<li>Describe the location of the parathyroid glands.<\/li>\n<li>Name and describe the actions of the parathyroid hormone.<\/li>\n<li>Describe the stimulus for and control of the release of parathyroid hormone. Identify the type of feedback <span style=\"font-family: inherit;font-size: inherit\">mechanism <\/span>involved.<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>XII.<\/strong> Describe the function and secretion of hormones released by the adrenal gland.<\/p>\n<ol>\n<li>Describe the location and the two general divisions of the adrenal gland.<\/li>\n<li>Name the three general classes of hormones produced by the adrenal cortex.<\/li>\n<li>Identify the major mineralocorticoid and describe the stimuli for its release, and the effects of its action.<\/li>\n<li>Identify the major glucocorticoid and describe the stimuli for its release, and the effects of its action.<\/li>\n<li>Name and describe the actions and stimulus of the third group of hormones released by the adrenal cortex.<\/li>\n<li>Name and describe the actions of the two hormones released by the adrenal medulla.<\/li>\n<li>Name two physical and two psychological stressors.<\/li>\n<li>Name and describe the three stages of the general adaptation syndrome. For each stage, identify the major hormone involved, its effects and either the purpose of the stage or its end result.<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>XIII.<\/strong> Describe the function and secretion of hormones released by the pancreas.<\/p>\n<ol>\n<li>Describe the location of the pancreas.<\/li>\n<li>Explain the exocrine and endocrine nature of the pancreas, including the name of the clusters of cells, and individual cell types that produce insulin and glucagon.<\/li>\n<li>Define gluconeogenesis, glycogenolysis and glycogenesis.<\/li>\n<li>Describe the stimulus for the release of, and three actions of, glucagon. Identify the type of feedback mechanism involved.<\/li>\n<li>Describe the stimulus for the release of, and five actions of, insulin. Identify the type of feedback mechanism involved.<\/li>\n<li>Name and describe the actions of the counterregulatory hormones (include glucagon).<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>XIV.<\/strong> Name the hormones produced by the following glands and describe their actions: ovaries, testes, stomach, duodenum, thymus and pineal gland.<\/p>\n<p class=\"hanging-indent\"><strong>XV.<\/strong> Describe prostaglandins, referring to their composition, where they are produced, where they generally have an effect, and four effects.<\/p>\n<\/div>\n<\/div>\n<h2><strong><a id=\"1\"><\/a>Part 1. General Properties of the Endocrine System<\/strong><\/h2>\n<h5 style=\"text-align: justify\"><strong><a id=\"1-1a\"><\/a>Introduction: The two general categories of glands in the body<\/strong><\/h5>\n<p style=\"text-align: justify\">The term \u2018gland\u2019 refers to any organ that produces a secretion. These secretions are produced by specialized cells in the glands from various components in the blood. There are two general categories of glands in the body: exocrine glands and endocrine glands.<\/p>\n<p>Exocrine glands are very diverse and include the salivary glands, mammary glands, sweat glands, pancreas, stomach, prostate, and several others. Their secretions are also varied &#8211; saliva, milk, sweat, digestive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_464\">enzymes<\/a> and fluids to accompany <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_465\">gametes<\/a> &#8211; just from the glands mentioned above. These glands are called exocrine glands because they have tubes or ducts to carry their secretions from the gland to another part of the body. These ducts may be simple tubes or complex, tree-like groups of ducts. Because of these tubes, the exocrine glands are also known as the ducted glands.<\/p>\n<p style=\"text-align: justify\">On the other hand, endocrine glands do not have ducts. Their secretions, called hormones, are carried to various body tissues by the blood and lymph, where they bind to receptors on target cells, inducing a characteristic response. Endocrine glands are sometimes called the ductless glands, and they all produce substances similar in nature, in that they are all hormones.<\/p>\n<p style=\"text-align: justify\">Some organs in the body contain both endocrine tissue and exocrine tissue. These organs include the pancreas, stomach and small intestine, all of which produce both hormones and digestive enzymes. The exocrine function of the pancreas (i.e., secretion of digestive enzymes into the duodenum) will be studied during the section on digestion. The endocrine function of the pancreas (release of the hormones insulin and glucagon, both of which are important in the control of blood sugar levels) will be studied later in this chapter.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"1-1b\"><\/a>General functions of endocrine hormones<\/strong><\/h5>\n<p style=\"text-align: justify\">You may never have thought of it this way, but when you send a text message to two friends to meet you at local cafe at six, you\u2019re sending digital signals that (you hope) will affect their behaviour\u2014even though they are some distance away. Similarly, endocrine glands send chemical signals (hormones) to other cells in the body that influence their behaviour. This long-distance intercellular communication, coordination, and control is critical for homeostasis, and it is the fundamental function of the endocrine system.<\/p>\n<p style=\"text-align: justify\">Although each has its own specific effects, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_460\">hormones <\/a> generally have the following functions:<\/p>\n<ul>\n<li style=\"text-align: justify\">Some hormones stimulate <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_459\">exocrine glands<\/a> to produce their secretions<\/li>\n<li style=\"text-align: justify\">Some stimulate other <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_458\">endocrine glands<\/a> to action<\/li>\n<li style=\"text-align: justify\">Some affect the growth, development and personality of an individual<\/li>\n<li style=\"text-align: justify\">Some regulate body chemistry such as the metabolism of cells<\/li>\n<li style=\"text-align: justify\">Some regulate the contraction of muscle tissues and nervous stimulation<\/li>\n<li style=\"text-align: justify\">Some control reproductive processes<\/li>\n<\/ul>\n<h5><strong><a id=\"1-1c\"><\/a>Hormonal Secretion: Regulation and Stimuli<\/strong><\/h5>\n<p><strong>Regulation of hormone secretion: <\/strong>Homeostasis is the condition in which the body\u2019s internal environment remains relatively constant within limits. One of the main functions of the endocrine system is to aid in the maintenance of homeostasis. To prevent abnormal hormone levels and a potential disease state, hormone levels must be tightly controlled. The body maintains this control by balancing hormone production and degradation. Feedback mechanisms govern the initiation and maintenance of most hormone secretion in response to various stimuli.<\/p>\n<p style=\"text-align: justify\">The concept of homeostasis and the mechanisms of feedback mechanisms were presented in Homeostasis unit of the Biology 1103\/1109 textbook (for review, refer to: <a href=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/chapter\/unit-8-homeostasis\/\">https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/chapter\/unit-8-homeostasis\/<\/a>). Recall that there are two types of feedback mechanisms: positive and negative. Positive feedback mechanisms intensify a change in the body\u2019s physiological condition rather than reversing it and result in a definite end event. An example of a hormonally based positive feedback mechanism involves the release of oxytocin during childbirth. The initial release of oxytocin begins to signal the uterine muscles to contract, which pushes the fetus toward the cervix, causing it to stretch. This, in turn, signals the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_391\">pituitary gland<\/a> to release more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_471\">oxytocin<\/a>, causing labour contractions to intensify. This will bring about the final event of childbirth, after which the release of oxytocin decreases.<\/p>\n<p style=\"text-align: justify\">However, the more common method of hormone regulation is the negative feedback mechanism, which generally is involved in the continual maintenance of a characteristic within limits. Hormonally based negative feedback mechanisms are characterized by the inhibition of further secretion of a hormone in response to adequate levels of that hormone (as determined by the amount of the hormone in the blood, or by the extent of the effect that the hormone has had). This allows blood levels of the hormone to be regulated within a narrow range.<\/p>\n<p><strong>Stimuli for hormonal secretion: <\/strong>The stimulus for the levels of a particular hormone can be humoral, i.e., blood levels of non-hormone chemicals such as nutrients or ions. Changes in such levels can cause the release or inhibition of a hormone (under negative feedback control) to maintain homeostasis. For example, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_409\">osmoreceptors <\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_392\">hypothalamus <\/a> detect changes in blood <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_410\">osmolarity <\/a> (the concentration of solutes in the blood plasma) and will signal the hypothalamus to release greater or lesser amounts of antidiuretic hormone (ADH) to keep the levels of solutes in the blood within normal limits. The control of blood glucose levels by the pancreas is another example of such stimulation. Responding directly to the level of glucose in the blood, cells in the pancreas release appropriate amounts of the hormones insulin and glucagon to maintain normal blood glucose levels. A final example of response to the level of a nutrient or ion in the blood is the regulation of levels of calcium by the parathyroid gland, which responds to changes in calcium levels in the blood with the secretion of varying levels of parathyroid hormone. All these mechanisms will be covered in greater detail later in this chapter.<\/p>\n<p style=\"text-align: justify\">The stimulus for the secretion of a hormone may also be the presence of another hormone produced by a different endocrine gland. Such hormonal stimuli often involve the hypothalamus, which produces releasing and inhibiting hormones that control the secretion of a variety of pituitary hormones, that in turn, may affect other endocrine glands in the body. These secretions are also controlled through negative feedback mechanisms. An example of such a negative feedback mechanism is the release of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_412\">glucocorticoid <\/a> hormones from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_446\">adrenal glands<\/a>, as directed by the hypothalamus and pituitary gland (this will also be covered in more detail later in this chapter). As the secretion of glucocorticoid from the adrenal glands cause concentrations of this hormone in the blood to rise, the hypothalamus and pituitary gland reduce their release of hormones that caused this secretion, thus signaling to the adrenal glands to decrease glucocorticoid secretion (<a class=\"rId8\" href=\"https:\/\/pressbooks.bccampus.ca\/dcbiol12031209\/chapter\/17-2-hormones\/\"><span class=\"import-Hyperlink\">Figure<\/span><\/a> 1).<\/p>\n<figure style=\"width: 1117px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2019\/04\/image1.jpeg\" alt=\"image\" width=\"1117\" height=\"1094\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 1. Negative Feedback Mechanism.<\/strong> The release of adrenal glucocorticoids is stimulated by the release of hormones from the hypothalamus and pituitary gland. This signaling is inhibited when glucocorticoid levels become elevated by causing negative signals to the pituitary gland and hypothalamus.<\/figcaption><\/figure>\n<h5><strong><a id=\"1-1d\"><\/a>Types of Hormones<\/strong><\/h5>\n<p style=\"text-align: justify\">The hormones of the human body can be divided into two major groups on the basis of their chemical structure. Hormones derived from amino acids include amines, peptides, and proteins. Those derived from lipids include steroids (<span class=\"import-Hyperlink\">Table<\/span><span class=\"import-Hyperlink\"> 1<\/span>). These chemical groups affect a hormone\u2019s distribution, the type of receptors it binds to, and other aspects of its function.<\/p>\n<p><strong>Amine Hormones<\/strong><\/p>\n<p style=\"text-align: justify\">Hormones derived from the modification of amino acids are referred to as amine hormones. Examples these include the metabolism-regulating thyroid hormones, as well epinephrine and norepinephrine, which play a role in the fight-or-flight response.<\/p>\n<p><strong>Peptide and Protein Hormones<\/strong><\/p>\n<p style=\"text-align: justify\">Whereas the amine hormones are derived from a single <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_447\">amino acid<\/a>, peptide and protein hormones consist of multiple amino acids that link to form an amino acid chain. Peptide hormones consist of short chains of amino acids, whereas protein hormones are longer polypeptides.<\/p>\n<p style=\"text-align: justify\">An example of a peptide hormone is antidiuretic hormone (ADH), a pituitary hormone important in fluid balance. Examples of protein hormones include growth hormone, which is produced by the pituitary gland, and follicle-stimulating hormone (FSH), which helps stimulate the maturation of eggs in the ovaries and sperm in the testes.<\/p>\n<p><strong>Steroid Hormones<\/strong><\/p>\n<p style=\"text-align: justify\">The primary hormones derived from lipids are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_448\">steroids<\/a>. Steroid hormones are derived from the lipid cholesterol. For example, the reproductive hormones testosterone and the estrogens\u2014which are produced by the gonads (testes and ovaries)\u2014are steroid hormones. The adrenal glands produce the steroid hormone aldosterone, which is involved in osmoregulation, and cortisol, which plays a role in metabolism.<\/p>\n<p style=\"text-align: justify\">Like cholesterol, steroid hormones are not soluble in water (they are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_469\">hydrophobic<\/a>). Because blood is water-based, lipid-derived hormones must travel to their target cell bound to a transport protein. This more complex structure extends the half-life of steroid hormones to much longer than that of hormones derived from amino acids. A hormone\u2019s half-life is the time required for half the concentration of the hormone to be degraded. For example, the lipid-derived hormone <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_472\">cortisol<\/a> has a half-life of approximately 60 to 90 minutes. In contrast, the amino acid\u2013derived hormone <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_449\">epinephrine <\/a> has a half-life of approximately one minute.<\/p>\n<h5><strong><a id=\"1-1e\"><\/a>Pathways of Hormone Action<\/strong><\/h5>\n<p style=\"text-align: justify\">Although a given hormone may travel throughout the body in the bloodstream, it will affect the activity only of its target cells; that is, cells with receptors for that particular hormone. The message a hormone sends is received by a\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_389\">hormone receptor<\/a><\/strong>, a protein located either inside the cell or within the cell membrane. The receptor will process the message by initiating other signaling events or cellular\u00a0mechanisms that result in the target cell\u2019s response. Hormone receptors recognize molecules with specific shapes and side groups, and respond only to those hormones that are recognized. The same type of receptor may be located on cells in different body tissues, and trigger somewhat different responses. Thus, the response triggered by a hormone depends not only on the hormone, but also on the target cell.<\/p>\n<figure style=\"width: 1046px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image2.jpeg\" alt=\"image\" width=\"1046\" height=\"1329\" \/><figcaption class=\"wp-caption-text\"><strong>Table 1. Amine, Peptide, Protein, and Steroid Hormone Structure<\/strong> (the structural formulae are not required as examinable material).<\/figcaption><\/figure>\n<p style=\"text-align: justify\">Once the target cell receives the hormone signal, it can respond in a variety of ways. The response may include the stimulation of protein synthesis, activation or deactivation of enzymes, alteration in the permeability of the cell membrane, altered rates of mitosis and cell growth, and stimulation of the secretion of products. Moreover, a single hormone may be capable of inducing different responses in a given cell.<\/p>\n<figure style=\"width: 937px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image3.jpeg\" alt=\"image\" width=\"937\" height=\"621\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 2. Binding of Lipid-Soluble Hormones.<\/strong> A steroid hormone directly initiates the production of proteins within a target cell. Steroid hormones easily diffuse through the cell membrane. The hormone binds to its receptor in the cytosol, forming a receptor\u2013hormone complex. The receptor\u2013hormone complex then enters the nucleus and binds to the target gene on the DNA. Transcription of the gene creates a messenger RNA that is translated into the desired protein within the cytoplasm.<\/figcaption><\/figure>\n<p><strong>Pathways Involving Intracellular Hormone Receptors: <\/strong>Intracellular hormone receptors are located inside the cell. Hormones that bind to this type of receptor must be able to cross the cell membrane. Steroid hormones are derived from cholesterol and therefore can readily diffuse through the lipid bilayer of the cell membrane to reach the intracellular receptor (<span class=\"import-Hyperlink\">Figure 2<\/span>). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_450\">Thyroid <\/a> hormones are also lipid-soluble and can enter the cell. Both hormones bind to DNA within the nucleus and trigger protein synthesis. The particular proteins synthesized will exert an effect.<\/p>\n<p><strong>Pathways Involving Cell Membrane Hormone Receptors: <\/strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_468\">Hydrophilic<\/a>, or water-soluble, hormones are unable to diffuse through the lipid bilayer of the cell membrane and must therefore pass on their message to a receptor located at the surface of the cell (Figure 3). Except for thyroid hormones, which are lipid-soluble, all amino acid\u2013derived hormones bind to cell membrane receptors that are located, at least in part, on the extracellular surface of the cell membrane. Therefore, they do not directly affect the production of proteins, but instead initiate a signaling cascade (a series of sequential activation of enzymes within the cell) that can trigger a wide variety of effects, from nutrient metabolism to the synthesis of different hormones and other products. The effects vary according to the type of target cell and which signaling cascade is activated inside the cell. Examples of hormones that use this mechanism include calcitonin, which is important for bone construction and regulating blood calcium levels, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_451\">glucagon<\/a>, which affects blood glucose levels.<\/p>\n<p style=\"text-align: justify\">Overall, such signaling cascades significantly increase the efficiency, speed, and specificity of the hormonal response, as thousands of signaling events can be initiated simultaneously in response to a very low concentration of hormone in the bloodstream, so the action of the hormone can be rapid and substantial. Additionally, the duration of this type of hormone signal is short.<\/p>\n<figure style=\"width: 965px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image4.jpeg\" alt=\"image\" width=\"965\" height=\"731\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 3. Binding of Water-Soluble Hormones.<\/strong> Water-soluble hormones cannot diffuse through the cell membrane. These hormones must bind to a surface cell-membrane receptor. The receptor then initiates a cell-signaling pathway within the cell involving G proteins, adenylyl cyclase, the secondary messenger cyclic AMP (cAMP), and protein kinases. In the final step, these protein kinases phosphorylate proteins in the cytoplasm. This activates proteins in the cell that carry out the changes specified by the hormone. (The specific steps of the cell-signaling pathway are not required as examinable material).<\/figcaption><\/figure>\n<h5 style=\"text-align: justify\"><strong><a id=\"1-1f\"><\/a>Comparison of the endocrine and nervous systems<\/strong><\/h5>\n<p style=\"text-align: justify\">Communication is a process in which a sender transmits signals to one or more receivers to control and coordinate actions. The part that the endocrine system plays in this has been stated, however in the human body, another major organ system participates in relatively \u201clong distance\u201d communication: the nervous system. Together, these two systems are primarily responsible for maintaining <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_452\">homeostasis <\/a> in the body. Although both systems function to allow communication within the body, there are some significant differences in the anatomy and physiology and thus how the function is carried out between the endocrine and nervous systems.<\/p>\n<p style=\"text-align: justify\">The <strong>nervous system<\/strong> uses two types of intercellular communication\u2014electrical and chemical signaling\u2014either by the direct action of an electrical potential, or in the latter case, through the action of chemical neurotransmitters such as serotonin or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_454\">norepinephrine<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_453\">Neurotransmitters <\/a> act locally and rapidly. When an electrical signal in the form of an action potential arrives at a synaptic terminal, it results in the release of neurotransmitters, which diffuse across the synaptic cleft (the gap between a sending neuron and a receiving neuron or muscle cell). Once the neurotransmitters interact (bind) with receptors on the receiving (post-synaptic) cell, the receptor stimulation is transduced into a response such as continued electrical signaling or modification of cellular response. The target cell responds within milliseconds of receiving the chemical \u201cmessage\u201d; this response then ceases very quickly once the neural signaling ends. In this way, neural communication enables body functions that involve quick, brief actions, such as movement, sensation, and cognition.<\/p>\n<p style=\"text-align: justify\">In contrast, the <strong>endocrine system <\/strong>uses just one method of communication: chemical signaling through <strong>hormones<\/strong>, which are secreted into the extracellular fluid. As previously stated, hormones are transported (primarily) via the bloodstream throughout the body, where they bind to receptors on target cells, inducing a characteristic response. As a result, endocrine signaling requires more time than neural signaling to prompt a response in target cells, though the precise amount of time varies with different hormones. For example, the hormones released when you are confronted with a dangerous or frightening situation, called the fight-or-flight response, occur by the release of adrenal hormones\u2014<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_449\">epinephrine <\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_454\">norepinephrine<\/a>\u2014within seconds. In contrast, it may take up to 48 hours for target cells to respond to certain reproductive hormones. Similarly, due to the mechanism of transmission of hormonal signals, the effect tends to last longer than a nervous stimulation.<\/p>\n<figure style=\"width: 171px\" class=\"wp-caption alignnone\"><a href=\"http:\/\/openstaxcollege.org\/l\/hormonebind\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image5.png\" alt=\"image\" width=\"171\" height=\"170\" \/><\/a><figcaption class=\"wp-caption-text\">Visit <a href=\"http:\/\/openstaxcollege.org\/l\/hormonebind\">this link<\/a> to watch an animation of the events that occur when a hormone binds to a cell membrane receptor. Direct link: <a href=\"http:\/\/openstaxcollege.org\/l\/hormonebind\">http:\/\/openstaxcollege.org\/l\/hormonebind<\/a><\/figcaption><\/figure>\n<p style=\"text-align: justify\">In addition, endocrine signaling is typically less specific than neural signaling. The same hormone may play a role in a variety of different physiological processes depending on the target cells involved. For example, the hormone <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_471\">oxytocin <\/a> promotes uterine contractions in women in labour. It is also important in breastfeeding and may be involved in the sexual response and in feelings of emotional attachment in both males and females.<\/p>\n<p style=\"text-align: justify\">In general, the nervous system involves quick responses to rapid changes in the external environment, and the endocrine system is usually slower acting\u2014taking care of the internal environment of the body, maintaining homeostasis, and controlling reproduction (Table 2).<\/p>\n<figure style=\"width: 150px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image6.png\" alt=\"image\" width=\"150\" height=\"150\" \/><figcaption class=\"wp-caption-text\">Watch <a href=\"https:\/\/youtu.be\/eWHH9je2zG4\">this Crash Course video<\/a> for an overview of the endocrine system! Direct link: <a href=\"https:\/\/youtu.be\/eWHH9je2zG4\">https:\/\/youtu.be\/eWHH9je2zG4<\/a><\/figcaption><\/figure>\n<p style=\"text-align: justify\">So how does the fight-or-flight response that was mentioned earlier happen so quickly if hormones are usually slower acting? It is because the two systems are connected. It is the fast action of the nervous system in response to the danger in the environment that stimulates the adrenal glands to secrete their hormones. As a result, the nervous system can cause rapid endocrine responses to keep up with sudden changes in both the external and internal environments when necessary.<\/p>\n<table style=\"width: 100%;height: 196px\">\n<caption><strong>Table 2<\/strong>. Major characteristics of endocrine and nervous systems<\/caption>\n<thead>\n<tr style=\"height: 1pt\">\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"col\"><\/th>\n<th class=\"TableGrid-C\" style=\"background-color: #d0cece;vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\" scope=\"col\"><strong>Endocrine system<\/strong><\/th>\n<th class=\"TableGrid-C\" style=\"background-color: #d0cece;vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\" scope=\"col\"><strong>Nervous system<\/strong><\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Signaling mechanism(s)<\/th>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Chemical<\/td>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Chemical \/ electrical<\/td>\n<\/tr>\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Primary chemical signal<\/th>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Hormones<\/td>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Neurotransmitters<\/td>\n<\/tr>\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Distance travelled by chemical signal<\/th>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Long or short<\/td>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Always short<\/td>\n<\/tr>\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Response time<\/th>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Fast or slow<\/td>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Always fast<\/td>\n<\/tr>\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Duration of response<\/th>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Longer than nervous<\/td>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Very short<\/td>\n<\/tr>\n<tr class=\"TableGrid-R\" style=\"height: 1pt\">\n<th class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 217.906px;height: 28px\" scope=\"row\">Environment targeted<\/th>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 122.906px;height: 28px\">Internal<\/td>\n<td class=\"TableGrid-C\" style=\"vertical-align: middle;border: 0.5pt solid windowtext;width: 138.906px;height: 28px\">Internal and external<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2 style=\"text-align: justify\"><strong><a id=\"2\"><\/a>Part 2. Major endocrine organs and their secretions<\/strong><\/h2>\n<p style=\"text-align: justify\">The major endocrine glands are shown in Figure 4, and are listed along with their associated hormones and their effects in <a href=\"#1-3\">Table 3<\/a>.<\/p>\n<figure style=\"width: 696px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image1-10.png\" alt=\"image\" width=\"696\" height=\"598\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 4. Endocrine System.<\/strong> Endocrine glands and cells are located throughout the body and play an important role in homeostasis.<\/figcaption><\/figure>\n<h5><strong><a id=\"1-2a\"><\/a>The Hypothalamus and Pituitary Gland<\/strong><\/h5>\n<p style=\"text-align: justify\">The hypothalamus\u2013pituitary complex can be thought of as the \u201ccommand centre\u201d of the endocrine system for basically two reasons. Besides secreting several hormones that directly produce responses in target tissues, it secretes hormones that regulate the synthesis and secretion of hormones of other endocrine glands. In addition, the hypothalamus\u2013pituitary complex coordinates the messages of the endocrine and nervous systems. In many cases, a stimulus received by the nervous system must pass through the hypothalamus\u2013pituitary complex to be translated into hormones that can initiate a response.<\/p>\n<p style=\"text-align: justify\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_392\"><strong>hypothalamus<\/strong> <\/a> is a structure of the diencephalon of the brain located anterior and inferior to the thalamus (Figure 5). The hypothalamus is anatomically and functionally related to the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_391\">pituitary gland<\/a><\/strong> (or hypophysis), a bean-sized organ suspended from it by a stem called the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_390\"><strong>infundibulum<\/strong> <\/a> (or pituitary stalk).<\/p>\n<figure style=\"width: 1077px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image9.png\" alt=\"image\" width=\"1077\" height=\"626\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 5. Hypothalamus\u2013Pituitary Complex.<\/strong> The hypothalamus region lies inferior and anterior to the thalamus. It connects to the pituitary gland by the stalk-like infundibulum. The pituitary gland consists of an anterior and posterior lobe, with each lobe secreting different hormones in response to signals from the hypothalamus.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">The <strong>pituitary gland<\/strong> is cradled within a cup-like hollow in the sphenoid bone of the skull. It consists of two lobes that arise from different parts of embryonic tissue: the anterior pituitary (also known as the adenohypophysis) is glandular tissue that develops from the primitive digestive tract, whereas the posterior pituitary (neurohypophysis) is neural tissue that is essentially an extension of the hypothalamus.<\/p>\n<p style=\"text-align: justify\"><strong>Hormonal secretion by the hypothalamus: <\/strong>All of the hormones that the hypothalamus produces either are directly secreted by the hypothalamus and control the release of hormones by the anterior pituitary (six of these will be discussed below) or are stored in and released by the posterior pituitary (there are two, as presently discussed).<\/p>\n<p style=\"text-align: justify\"><strong>Hypothalamic control of anterior pituitary gland secretion: <\/strong>The secretion of all hormones from the anterior pituitary is regulated by two classes of hormones secreted by the hypothalamus: releasing hormones that stimulate the secretion of hormones from the anterior pituitary, and inhibiting hormones that inhibit secretion (i.e., the anterior pituitary never increases or decreases the release of one of its hormones, without being signaled to do so by the hypothalamus).<\/p>\n<p style=\"text-align: justify\">Hypothalamic hormones that control the anterior pituitary are secreted by neurons in the hypothalamus and enter the anterior pituitary through blood vessels (Figure 6). Within the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_390\">infundibulum <\/a> (the connecting tissue between the hypothalamus and the pituitary) is a bridge of capillaries that connects the hypothalamus to the anterior pituitary. This network, called the <strong>hypophyseal portal system<\/strong>, allows hypothalamic hormones to be transported to the anterior pituitary without first entering the systemic circulation. Hormones produced by the anterior pituitary in response to these releasing or inhibiting hormones sent by the hypothalamus then enter a secondary capillary plexus, and from there drain into the general circulation.<\/p>\n<figure style=\"width: 1154px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image10.png\" alt=\"image\" width=\"1154\" height=\"996\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 6. Anterior Pituitary.<\/strong> The hypothalamus produces separate hormones that stimulate or inhibit hormone production in the anterior pituitary. Hormones from the hypothalamus reach the anterior pituitary via the hypophyseal portal system.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">Four of the hormones the hypothalamus produces act as releasing factors which stimulate the secretion of five separate hormones from the anterior pituitary gland (Figure 7). These four releasing hormones are named after the pituitary hormones whose secretions they stimulate:<\/p>\n<ul>\n<li style=\"text-align: justify\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_1250\">Adrenocorticotropic hormone releasing hormone<\/a> (ACTHRH, or CRH for corticotropin releasing hormone)<\/li>\n<li style=\"text-align: justify\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_1249\">Thyroid stimulating hormone releasing hormone<\/a> (TSHRH, or TRH for thyrotropin releasing hormone)<\/li>\n<li style=\"text-align: justify\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_1248\">Growth hormone releasing hormone (GHRH)<\/a><\/li>\n<li style=\"text-align: justify\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_1247\">Gonadotropin releasing hormone (GnRH)<\/a>, which stimulates the release of\u00a0hormones known as gonadotropins: follicle stimulating hormone (FSH) and luteinizing hormone (LH)<\/li>\n<\/ul>\n<p style=\"text-align: justify\">The hypothalamus also produces inhibiting factors, including <em>growth hormone inhibiting hormone<\/em> (GHIH) and <em>prolactin inhibiting hormone<\/em> (PIH).<\/p>\n<p style=\"text-align: justify\">Cells of the hypothalamus also produce hormones that are stored in and secreted by the posterior pituitary, rather than being secreted from the hypothalamus itself.\u00a0 The hypothalamus produces the hormones oxytocin and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_473\">antidiuretic hormone<\/a> (Figure 7), both of which are transported, stored in and then released from the posterior pituitary gland (discussed in the section describing secretions of the posterior pituitary) (Fig. 8).<\/p>\n<figure id=\"attachment_1520\" aria-describedby=\"caption-attachment-1520\" style=\"width: 868px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1520 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3.png\" alt=\"\" width=\"868\" height=\"547\" srcset=\"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3.png 868w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3-300x189.png 300w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3-768x484.png 768w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3-65x41.png 65w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3-225x142.png 225w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2019\/08\/Picture1-3-350x221.png 350w\" sizes=\"auto, (max-width: 868px) 100vw, 868px\" \/><\/a><figcaption id=\"caption-attachment-1520\" class=\"wp-caption-text\"><strong>Figure 7. Hormones of the hypothalamus.<\/strong> The hypothalamus releases hormones that either control the release of other hormones from the anterior pituitary, or produces hormones (ADH and oxytocin) that are released by the posterior pituitary.<\/figcaption><\/figure>\n<figure style=\"width: 957px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image11.png\" alt=\"image\" width=\"957\" height=\"772\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 8. Posterior Pituitary.<\/strong> Neurosecretory cells in the hypothalamus release oxytocin (OT) or ADH into the posterior lobe of the pituitary gland. These hormones are stored or released into the blood via the capillary plexus.<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Hormonal secretion by the anterior pituitary: <\/strong>The anterior pituitary produces several hormones, including <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_474\">growth hormone<\/a> (GH) and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_475\">prolactin<\/a>, neither of which affect other endocrine glands, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_476\">thyroid-stimulating hormone<\/a> (TSH), <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_1374\">adrenocorticotropic hormone (ACTH)<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_478\">follicle-stimulating hormone<\/a> (FSH), and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_479\">luteinizing hormone<\/a> (LH). Of the hormones of the anterior pituitary, these last four (TSH, ACTH, FSH, and LH) are collectively referred to as tropic hormones (the suffix \u201ctropic\u201d = \u201cturning towards \/ having an influence on\u201d) because they travel to and affect the function of other endocrine glands.<\/p>\n<p><strong>Growth Hormone: <\/strong>The endocrine system regulates the growth of the human body, protein synthesis, and cellular replication. A major hormone involved in this process is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_474\">growth hormone<\/a> (GH), also called somatotropin (\u201csoma\u201d means body; \u201ctropin\u201d means going towards\/having an effect on) \u2014a protein hormone produced and secreted by the anterior pituitary gland. Its primary function is anabolic; it promotes protein synthesis and tissue building, increases catabolism of fats and generally slows down the catabolism of carbohydrates (thus helping to maintain blood glucose levels) (Figure 9). GH levels are controlled by the release of growth hormone-releasing hormone (GHRH) and growth hormone-inhibiting hormone (GHIH, also known as somatostatin) from the hypothalamus.<\/p>\n<figure style=\"width: 962px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image12.png\" alt=\"image\" width=\"962\" height=\"816\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 9. Hormonal Regulation of Growth.<\/strong> Growth hormone (GH) directly accelerates the rate of protein synthesis in skeletal muscle and bones. Insulin-like growth factor 1 (IGF-1) is activated by growth hormone and indirectly supports the formation of new proteins in muscle cells and bone.<\/figcaption><\/figure>\n<p><strong style=\"text-align: justify;font-size: 1em\">Prolactin: <\/strong><span style=\"text-align: justify;font-size: 1em\">As its name implies, <\/span><strong style=\"text-align: justify;font-size: 1em\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_475\">prolactin<\/a><\/strong><span style=\"text-align: justify;font-size: 1em\"> (<\/span><strong style=\"text-align: justify;font-size: 1em\">PRL<\/strong><span style=\"text-align: justify;font-size: 1em\">) promotes lactation (milk production) in women. During pregnancy, it contributes to the development of the mammary glands, and after birth, it stimulates the mammary glands to produce breast milk. (As will be noted later, the let-down (release) of milk from the breasts occurs in response to stimulation from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_471\">oxytocin<\/a>.)<\/span><\/p>\n<p style=\"text-align: justify\">In a non-pregnant woman, prolactin secretion is inhibited by prolactin-inhibiting hormone (PIH), which is actually the neurotransmitter dopamine, and is released from neurons in the hypothalamus. Only during pregnancy do prolactin levels rise in response to prolactin-releasing hormone (PRH) from the hypothalamus.<\/p>\n<p style=\"text-align: justify\"><strong>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_408\">Tropic <\/a> Hormones<\/strong><\/p>\n<p style=\"text-align: justify\"><strong>Thyroid-Stimulating Hormone: <\/strong>The activity of the thyroid gland is regulated by <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_476\">thyroid-stimulating hormone<\/a><\/strong> (<strong>TSH<\/strong>), also called thyrotropin, released from the anterior pituitary. In turn, TSH is released from the anterior pituitary in response to thyrotropin-releasing hormone (TRH or TSHRH) from the hypothalamus. As discussed shortly, TSH triggers the secretion of thyroid hormones by the thyroid gland. In a classic negative feedback mechanism, elevated levels of thyroid hormones in the bloodstream then trigger a decrease in production of TRH and subsequently TSH.<\/p>\n<p style=\"text-align: justify\"><strong>Adrenocorticotropic Hormone: <\/strong>The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_1374\">adrenocorticotropic hormone<\/a><\/strong>\u00a0(<strong>ACTH<\/strong>), also called corticotropin, stimulates the adrenal cortex (the outer layer of the adrenal glands) to secrete corticosteroid hormones such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_472\">cortisol<\/a>.<\/p>\n<p style=\"text-align: justify\">The release of ACTH is regulated by the corticotropin-releasing hormone (CRH) from the hypothalamus in response to normal physiologic rhythms (The release of ACTH typically peaks in the morning, and reaches its lowest levels in late evening). A variety of stressors can also influence its release, and the role of ACTH in the stress response is discussed later in this unit.<\/p>\n<p style=\"text-align: justify\"><strong>Follicle-Stimulating Hormone and Luteinizing Hormone: <\/strong>Several endocrine glands secrete a variety of hormones that control the development and regulation of the reproductive system (these glands include the anterior pituitary, the adrenal cortex, and the gonads &#8211; the testes in males and the ovaries in females). Much of the development of the reproductive system occurs during puberty and is marked by the development of sex-specific characteristics in both male and female adolescents. Puberty is initiated by <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_480\">gonadotropin<\/a>-releasing hormone<\/strong> (<strong>GnRH<\/strong>), a hormone produced and secreted by the hypothalamus. GnRH stimulates the anterior pituitary to secrete <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_394\">gonadotropins<\/a><\/strong>\u2014hormones that regulate the function of the gonads. The levels of GnRH are regulated through a negative feedback mechanism; high levels of reproductive hormones inhibit the release of GnRH. Throughout life, gonadotropins regulate reproductive function and, in the case of women, the onset and cessation of reproductive capacity.<\/p>\n<p style=\"text-align: justify\">The gonadotropins include two hormones: 1) <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_478\">Follicle-stimulating hormone<\/a><\/strong> (<strong>FSH<\/strong>) which stimulates the production and maturation of sex cells, or gametes (ova in females and sperm in males). FSH also promotes follicular growth; these follicles then release estrogens in the ovaries. 2) <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_479\">Luteinizing hormone<\/a><\/strong> (<strong>LH<\/strong>) triggers ovulation, as well as the production of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_481\">estrogens <\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_482\">progesterone <\/a> by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_483\">ovaries<\/a>. LH stimulates production of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_485\">testosterone<\/a> by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_484\">testes<\/a>.<\/p>\n<p style=\"text-align: justify\"><strong>Hormonal secretion by the posterior pituitary: <\/strong>The posterior pituitary is actually an extension of neurons that originate in two specific <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_486\">nuclei <\/a> (clusters of neuronal cell bodies) in the hypothalamus. While the cell bodies of these neurons rest in the hypothalamus, their axons descend as the hypothalamic\u2013hypophyseal tract within the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_390\">infundibulum<\/a>, and end in axon terminals that comprise the posterior pituitary (Figure 7).<\/p>\n<p style=\"text-align: justify\">The posterior pituitary gland does not produce hormones, but rather stores and secretes hormones produced by the hypothalamus. Neuronal cell bodies of one group of cells in the hypothalamus produces the hormone <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_471\">oxytocin<\/a>, whereas neuronal cell bodies of another group of cells produces <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_473\">antidiuretic hormone<\/a> (ADH). These hormones then travel along the axons belonging to the respective neurons into storage sites in the axon terminals of the posterior pituitary. In response to later signals from the hypothalamus, the hormones are then released from the axon terminals into the bloodstream.<\/p>\n<p style=\"text-align: justify\"><strong>Oxytocin: <\/strong>When fetal development is complete, the peptide-derived hormone oxytocin (tocia- = \u201cchildbirth\u201d) stimulates uterine contractions and dilation of the cervix. Oxytocin is continually released throughout childbirth through a positive feedback mechanism that continues until birth.<\/p>\n<p style=\"text-align: justify\">Although the mother\u2019s high blood levels of oxytocin begin to decrease immediately following birth, oxytocin continues to play a role in maternal and newborn health. First, oxytocin is necessary for the milk ejection reflex (commonly referred to as \u201clet-down\u201d) in breastfeeding women. Secondly, in both males and females, oxytocin is thought to contribute to parent\u2013newborn bonding, known as attachment. In general, oxytocin is also thought to be involved in feelings of love and closeness, as well as in the sexual response.<\/p>\n<p style=\"text-align: justify\"><strong>Antidiuretic Hormone (ADH): <\/strong>ADH is an important hormone of the urinary system.\u00a0 The solute concentration of the blood, or blood <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_410\">osmolarity<\/a>, may change in response to the consumption of certain foods and fluids, as well as in response to disease, injury, medications, or other factors. Blood osmolarity is constantly monitored by <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_409\">osmoreceptors<\/a><\/strong>\u2014specialized cells within the hypothalamus that are particularly sensitive to the concentration of sodium ions and other solutes.<\/p>\n<p style=\"text-align: justify\">In response to high blood osmolarity, which can occur during dehydration or following a very salty meal, the osmoreceptors in the hypothalamus signal the posterior pituitary to release <strong>antidiuretic hormone<\/strong> (<strong>ADH<\/strong>). The target cells of ADH are located in the tubular cells of the kidneys. Its effect is to increase epithelial permeability to water, allowing increased water reabsorption. A greater concentration of water in the blood results in a reduced concentration of solutes. ADH is also known as vasopressin because, in very high concentrations, it causes constriction of blood vessels, which increases blood pressure by increasing peripheral resistance. The release of ADH is controlled by a negative feedback mechanism. As blood osmolarity decreases, the hypothalamic osmoreceptors sense the change and prompt a corresponding decrease in the secretion of ADH. As a result, less water is reabsorbed from the urine filtrate.<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_38\" aria-describedby=\"caption-attachment-38\" style=\"width: 514px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-32 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image4-10-Openstax-anterior-view-thyroid.png\" alt=\"\" width=\"514\" height=\"302\" srcset=\"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image4-10-Openstax-anterior-view-thyroid.png 514w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image4-10-Openstax-anterior-view-thyroid-300x176.png 300w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image4-10-Openstax-anterior-view-thyroid-65x38.png 65w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image4-10-Openstax-anterior-view-thyroid-225x132.png 225w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image4-10-Openstax-anterior-view-thyroid-350x206.png 350w\" sizes=\"auto, (max-width: 514px) 100vw, 514px\" \/><figcaption id=\"caption-attachment-38\" class=\"wp-caption-text\"><strong>Figure 10. Anterior view of thyroid gland.<\/strong><\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<h5><strong><a id=\"1-2b\"><\/a>The Thyroid Gland<\/strong><\/h5>\n<p style=\"text-align: justify\">A butterfly-shaped organ, the <strong>thyroid gland<\/strong> is located anterior to the trachea, just inferior to the larynx (Figure 10). The medial region, called the isthmus, is flanked by wing-shaped left and right lobes. Each of the thyroid lobes are embedded with parathyroid glands, primarily on their posterior surfaces. The thyroid gland produces and secretes two hormones: thyroid hormone and calcitonin.<\/p>\n<p style=\"text-align: justify\"><strong>Thyroid Hormone<\/strong><\/p>\n<p style=\"text-align: justify\">As with many other hormones, the release of thyroid hormone is under negative feedback control, as a result of stimulation by TSH (thyroid stimulating hormone) released by the anterior pituitary. Recall that TSH is stimulated in turn by the release of TSHRH (thyroid stimulating hormone releasing hormone) released by the hypothalamus. Thyroid hormone actually consists of two slightly different compounds: T<sub>3<\/sub> (triiodothyronine) and T<sub>4 <\/sub>(thyroxine). These compounds are often referred to as metabolic hormones because their levels influence the body\u2019s basal metabolic rate, which is the amount of energy used by the body to make ATP at rest. When T<sub>3<\/sub> and T<sub>4<\/sub> bind to intracellular receptors, they cause an increase in nutrient breakdown (thus causing a breakdown of fats and carbohydrates), and the increased use of oxygen to produce ATP. In addition, T<sub>3<\/sub> and T<sub>4<\/sub> initiate the transcription of genes involved in glucose oxidation. The process is inefficient, and an increased amount of heat is released as a byproduct of the increased rate of cellular respiration. This so-called calorigenic effect (calor- = \u201cheat\u201d) raises body temperature.<\/p>\n<p style=\"text-align: justify\">Adequate levels of thyroid hormones are also required for protein synthesis and for fetal and childhood tissue development and growth. They are especially critical for normal development of the nervous system both <em>in utero<\/em> and in early childhood, and they continue to support neurological function in adults.<\/p>\n<p style=\"text-align: justify\">These thyroid hormones also have a complex interrelationship with reproductive hormones, and deficiencies can influence libido, fertility, and other aspects of reproductive function. Finally, thyroid hormones increase the body\u2019s sensitivity to catecholamines (epinephrine and norepinephrine) from the adrenal medulla by upregulation of receptors in the blood vessels and the heart. When levels of T<sub>3<\/sub> and T<sub>4<\/sub> hormones are excessive, this effect accelerates the heart rate, strengthens the heartbeat, and increases blood pressure. Because thyroid hormones regulate metabolism, heat production, protein synthesis, and many other body functions, thyroid disorders can have severe and widespread consequences.<\/p>\n<p style=\"text-align: justify\">A symptom of many thyroid disorders is a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_395\">goiter<\/a><\/strong>, which is an increase in the overall size of the thyroid gland (Figure 11). Interestingly, a goiter can arise whether the thyroid gland is synthesizing too much or too little of thyroid hormone.<\/p>\n<p style=\"text-align: justify\">Consistent overstimulation of the thyroid gland that then produces more than normal amounts of thyroid hormone can occur in diseases such as Grave\u2019s disease. Such stimulation may result in an increase in the size of the thyroid gland (= goiter).<\/p>\n<p style=\"text-align: justify\">On the other hand, underactivity of the thyroid gland would result in lower amounts of thyroid hormone in the blood. This would decrease the negative feedback effect that thyroid hormone has on the production of TRH from the hypothalamus and TSH from the anterior pituitary. The levels of these compounds in the blood will then rise and stay elevated as long as the level of thyroid hormone remains low. This will continuously stimulate the thyroid gland, causing it to increase in size (= goiter). One of the causes for the inability of the thyroid gland to produce thyroid hormone in the first place is a condition known as <strong>simple goiter<\/strong>, which occurs when the body\u2019s intake of iodine (which is required for the production of thyroid hormone) is not sufficient for its needs.<\/p>\n<figure style=\"width: 797px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image15.jpeg\" alt=\"image\" width=\"797\" height=\"602\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 11. Goiter.<\/strong> (credit: \u201cAlmazi\u201d\/Wikimedia Commons)<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><strong>Calcitonin: <\/strong>The thyroid gland also secretes a hormone called calcitonin that is released in response to a rise in blood calcium levels. It appears to have a function in decreasing blood calcium concentrations by:<\/p>\n<ul style=\"text-align: justify\">\n<li>Inhibiting the activity of osteoclasts, bone cells that release calcium into the circulation by degrading bone matrix<\/li>\n<li>Increasing osteoblastic activity (thereby increasing deposition of calcium into bones)<\/li>\n<li>Decreasing calcium absorption in the intestines<\/li>\n<li>Increasing calcium loss in the urine<\/li>\n<\/ul>\n<p style=\"text-align: justify\">However, these functions are usually not significant in maintaining calcium homeostasis (people with long term increased or decreased calcitonin secretion due to disease usually do not show abnormal blood calcium levels), so the importance of calcitonin is not entirely understood. The production of calcitonin does however respond to levels of calcium in the blood (Figure 13), and pharmaceutical preparations of calcitonin are sometimes prescribed to reduce osteoclast activity in people with osteoporosis and to reduce the degradation of cartilage in people with osteoarthritis.<\/p>\n<p style=\"text-align: justify\">Calcium is critical for many biological processes, acting as a second messenger in many signaling pathways, and essential for muscle contraction, nerve impulse transmission, and blood clotting. The necessary tight regulation of blood calcium levels is mainly carried out by the parathyroid glands.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"1-2c\"><\/a>The Parathyroid Glands<\/strong><\/h5>\n<p style=\"text-align: justify\">The <strong>parathyroid glands<\/strong> are tiny, round structures usually found embedded in the posterior surface of the thyroid gland (Figure 12). A thick connective tissue capsule separates the glands from the thyroid tissue. Most people have four parathyroid glands. The primary functional cells of the parathyroid glands cells produce and secrete the <strong>parathyroid hormone<\/strong> (<strong>PTH<\/strong>) (also known as parathormone), the major hormone involved in the regulation of blood calcium levels.<\/p>\n<figure id=\"attachment_38\" aria-describedby=\"caption-attachment-38\" style=\"width: 453px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-34 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image5-10-Openstax-posterior-view-thyroid.png\" alt=\"\" width=\"453\" height=\"333\" srcset=\"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image5-10-Openstax-posterior-view-thyroid.png 453w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image5-10-Openstax-posterior-view-thyroid-300x221.png 300w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image5-10-Openstax-posterior-view-thyroid-65x48.png 65w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image5-10-Openstax-posterior-view-thyroid-225x165.png 225w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image5-10-Openstax-posterior-view-thyroid-350x257.png 350w\" sizes=\"auto, (max-width: 453px) 100vw, 453px\" \/><figcaption id=\"caption-attachment-38\" class=\"wp-caption-text\"><strong>Figure 12. Parathyroid Glands.<\/strong> The small parathyroid glands are embedded in the posterior surface of the thyroid gland.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">The parathyroid glands produce and secrete PTH, a peptide hormone, in response to low blood calcium levels (Figure 13). PTH secretion causes the increase in blood calcium via the following mechanisms:<\/p>\n<ul>\n<li style=\"text-align: justify\">Stimulating the activity of osteoclasts, bone cells that release calcium into the circulation by degrading bone matrix<\/li>\n<li style=\"text-align: justify\">Inhibiting osteoblastic activity (thereby decreasing deposition of calcium into bones)<\/li>\n<li style=\"text-align: justify\">Increasing calcium absorption in the intestines by initiating the production of the steroid hormone calcitriol (also known as 1,25-dihydroxyvitamin D), which is the active form of vitamin D3, in the kidneys. Calcitriol then stimulates increased absorption of dietary calcium by the intestines.<\/li>\n<li style=\"text-align: justify\">Decreasing calcium loss in the urine by causing increased reabsorption of calcium (and magnesium) in the kidney tubules from the urine filtrate<\/li>\n<\/ul>\n<p style=\"text-align: justify\">A negative feedback mechanism regulates the levels of PTH, with rising blood calcium levels inhibiting further release of PTH.<\/p>\n<figure id=\"attachment_38\" aria-describedby=\"caption-attachment-38\" style=\"width: 1186px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-35 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/1817_The_Role_of_Parathyroid_Hormone_in_Maintaining_Blood_Calcium_Homeostasis.jpg\" alt=\"\" width=\"1186\" height=\"1425\" srcset=\"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/1817_The_Role_of_Parathyroid_Hormone_in_Maintaining_Blood_Calcium_Homeostasis.jpg 1186w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/1817_The_Role_of_Parathyroid_Hormone_in_Maintaining_Blood_Calcium_Homeostasis-250x300.jpg 250w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/1817_The_Role_of_Parathyroid_Hormone_in_Maintaining_Blood_Calcium_Homeostasis-852x1024.jpg 852w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/1817_The_Role_of_Parathyroid_Hormone_in_Maintaining_Blood_Calcium_Homeostasis-768x923.jpg 768w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/1817_The_Role_of_Parathyroid_Hormone_in_Maintaining_Blood_Calcium_Homeostasis-65x78.jpg 65w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/1817_The_Role_of_Parathyroid_Hormone_in_Maintaining_Blood_Calcium_Homeostasis-225x270.jpg 225w, https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/1817_The_Role_of_Parathyroid_Hormone_in_Maintaining_Blood_Calcium_Homeostasis-350x421.jpg 350w\" sizes=\"auto, (max-width: 1186px) 100vw, 1186px\" \/><figcaption id=\"caption-attachment-38\" class=\"wp-caption-text\"><strong>Figure 13. Hormones Involved in Maintaining Blood Calcium Homeostasis.<\/strong> When blood calcium levels drop below the normal range, the release of parathyroid hormone increases and acts to increase calcium levels. When blood calcium levels rise beyond normal levels, the release of calcitonin from the thyroid gland increases and acts to decrease calcium levels.<\/figcaption><\/figure>\n<h5 style=\"text-align: justify\"><strong><a id=\"1-2d\"><\/a>The Adrenal Glands<\/strong><\/h5>\n<p style=\"text-align: justify\">The <strong>adrenal glands<\/strong> are wedges of glandular and neuroendocrine tissue adhering to the top of the kidneys by a fibrous capsule (Figure 14). The adrenal glands have a rich blood supply and experience one of the highest rates of blood flow in the body. The adrenal gland consists of an outer cortex of glandular tissue and an inner medulla of nervous tissue.<\/p>\n<figure style=\"width: 1102px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image21.png\" alt=\"image\" width=\"1102\" height=\"316\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 14. Adrenal Glands.<\/strong> Both adrenal glands sit atop the kidneys and are composed of an outer cortex and an inner medulla, all surrounded by a connective tissue capsule. The cortex can be subdivided into additional zones, all of which produce different types of hormones. LM \u00d7 204. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012). (Knowledge of the zones\u2019 names and responsibility for particular hormone production is not required as examinable material.)<\/figcaption><\/figure>\n<p><strong>Hormones of the adrenal cortex<\/strong><\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_411\">Mineralocorticoids<\/a><\/strong><\/p>\n<p style=\"text-align: justify\">The most superficial region of the adrenal cortex (zona glomerulosa) produces a group of hormones collectively referred to as <strong>mineralocorticoids<\/strong> because of their effect on body minerals, especially sodium and potassium. These hormones are essential for fluid and electrolyte balance.<\/p>\n<p style=\"text-align: justify\"><strong>Aldosterone<\/strong> is the major mineralocorticoid. It is important in the regulation of the concentration of sodium and potassium ions in urine, sweat, and saliva. For example, it is released in response to elevated blood K<sup>+<\/sup>, low blood Na<sup>+<\/sup>, low blood pressure, low blood volume and activation of the renin-angiotensin-aldosterone system (RAAS) (this hormone will be discussed again during the unit dealing with the renal system). In response, aldosterone increases the excretion of K<sup>+<\/sup> and the retention of Na<sup>+<\/sup>, which in turn increases blood volume and blood pressure.<\/p>\n<p style=\"text-align: justify\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_412\">Glucocorticoids<\/a><\/strong><\/p>\n<p style=\"text-align: justify\">The cells of the middle layer (zona fasciculata) produce hormones called <strong>glucocorticoids<\/strong> because of their role in glucose metabolism. The most important of these is <strong>cortisol<\/strong>. In response to long-term stressors, the hypothalamus secretes CRH, which in turn triggers the release of ACTH by the anterior pituitary. ACTH triggers the release of cortisol. The overall effect is to inhibit tissue building while stimulating the breakdown of stored nutrients to maintain adequate fuel supplies. In conditions of long-term stress, for example, cortisol promotes the catabolism of glycogen to glucose, the catabolism of stored triglycerides into fatty acids and glycerol, and the catabolism of muscle proteins into amino acids. Cortisol increases the body\u2019s resistance to stress by increasing muscle metabolism, maintaining the excitability of nerves and increasing the amount of sugars in the body by promoting <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_396\">gluconeogenesis<\/a><\/strong>, the conversion of fats and proteins into sugars.<\/p>\n<p style=\"text-align: justify\"><strong>Androgens<\/strong><\/p>\n<p style=\"text-align: justify\">The innermost layer of the cortex (zona reticularis) produces small amounts of sex hormones called <strong>androgens, <\/strong>which are converted into <strong>testosterone<\/strong> and <strong>estrogens<\/strong> in the tissues. The adrenal cortex serves as the source of sex hormones in an individual until the gonads mature at puberty. The sex hormones of the adrenal cortex play a role in the development of secondary sex characteristics in both males and females. In males, they further increase muscle development. It is interesting to note that the production of the cortical sex hormones is under the influence of adrenocorticotropic hormone from the anterior pituitary gland, and not follicle stimulating hormone or luteinizing hormone.<\/p>\n<p style=\"text-align: justify\"><strong>Hormones of the Adrenal Medulla<\/strong><\/p>\n<p style=\"text-align: justify\"><strong>Epinephrine and norepinephrine<\/strong> (also sometimes called adrenalin and noradrenalin): These two hormones are both involved in the response to fear, excitement and danger. They both increase blood pressure, and the rate and depth of breathing. Epinephrine, however, increases heart rate and blood sugar levels, whereas norepinephrine reduces the blood flow to the gut and skin.<\/p>\n<p style=\"text-align: justify\"><strong>The Stress Response<\/strong><\/p>\n<p style=\"text-align: justify\">One of the major functions of the adrenal gland is to respond to stress. Stress can be defined as some occurrence that disrupts homeostasis, and can be either physical or psychological or both. Physical stresses include exposing the body to injury, walking outside in cold and wet conditions without a coat on, or malnutrition. Psychological stresses include the perception of a physical threat, a fight with a loved one, or just a bad day at school.<\/p>\n<p style=\"text-align: justify\">The body responds in different ways to short-term stress and long-term stress following a pattern known as the <strong>general adaptation syndrome<\/strong>. The first stage of the general adaptation syndrome is called the\u00a0<strong>alarm reaction<\/strong>. This \u201cfight-or-flight\u201d response, the result of a short-term stressor, is mediated by the hormones epinephrine and norepinephrine from the adrenal medulla, as stimulated by the sympathetic nervous system. Their function is to prepare the body for extreme physical exertion by increasing the heart rate, dilating the airways, and other related responses. Once this stressor is relieved, the body quickly returns to normal.<\/p>\n<p style=\"text-align: justify\">If the stressor is not soon relieved, the body attempts to adapt to the stressor in the second stage called the\u00a0<strong>stage of resistance<\/strong>. The primary stress hormone at this stage is cortisol, secreted by the adrenal cortex as a result of signals sent by the hypothalamus and pituitary gland. Cortisol\u2019s effects are widespread. They include the maintenance of blood glucose through synthesizing glucose from compounds such as proteins (gluconeogenesis), and lipolysis so fatty acids can be used for energy by the body, thus preserving glucose. Additionally, the activity of the immune system and inflammation are reduced, as the resources of the body are directed towards dealing with the stress. The physiological adaptations during this stage allow the body to resist the most immediate negative effects of a longer-term stressor.<\/p>\n<p style=\"text-align: justify\">However, if the stressor continues for a longer term, the final stage of the stress response may occur. This is known as the\u00a0<strong>stage of exhaustion<\/strong>. At this point, the resources of the body have become depleted and individuals may begin to suffer depression, severe fatigue, or even a fatal heart attack. The continued release of cortisol and other hormones associated with long term stress can cause damage to a variety of organ systems, and this condition has been linked to many diseases such as rheumatoid arthritis, hypertension and gastrointestinal diseases.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"1-2e\"><\/a>The Endocrine Pancreas<\/strong><\/h5>\n<p style=\"text-align: justify\">The <strong>pancreas<\/strong> is a long, slender organ, most of which is located posterior to the bottom half of the stomach (Figure 15). Although it is primarily an exocrine gland, secreting a variety of digestive enzymes, the pancreas has an endocrine function. Its<strong> pancreatic islets<\/strong> &#8211;\u00a0clusters of cells formerly known as the islets of Langerhans &#8211; secrete the hormones glucagon and insulin.<\/p>\n<p style=\"text-align: justify\"><strong>Cells and Secretions of the Pancreatic Islets<\/strong><\/p>\n<p style=\"text-align: justify\">Cells residing in the pancreatic islets include the following two types of cells.\u00a0 The <strong>alpha cell<\/strong> produces the hormone glucagon and makes up approximately 20 percent of each islet. Glucagon plays an important role in blood glucose regulation; low blood glucose levels stimulate its release.\u00a0The <strong>beta cell<\/strong> produces the hormone insulin and makes up approximately 75 percent of each islet. Elevated blood glucose levels stimulate the release of insulin.<\/p>\n<figure style=\"width: 1092px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image22.png\" alt=\"image\" width=\"1092\" height=\"551\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 15. Pancreas.<\/strong> The pancreatic exocrine function involves the acinar cells secreting digestive enzymes that are transported into the small intestine by the pancreatic duct. Its endocrine function involves the secretion of insulin (produced by beta cells) and glucagon (produced by alpha cells) within the pancreatic islets. These two hormones regulate the rate of glucose metabolism in the body. The micrograph reveals pancreatic islets. LM \u00d7 760. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Regulation of Blood Glucose Levels by Insulin and Glucagon<\/strong><\/p>\n<p style=\"text-align: justify\">Glucose is required for cellular respiration and is the preferred fuel for all body cells. The body derives glucose from the breakdown of the carbohydrate-containing foods and drinks we consume. Glucose not immediately taken up by cells for fuel can be stored by the liver and muscles as glycogen or converted to triglycerides and stored in the adipose tissue. Hormones regulate both the storage and the utilization of glucose as required. Receptors located in the pancreas sense blood glucose levels, and subsequently the pancreatic cells secrete glucagon or insulin to maintain normal levels.<\/p>\n<p><strong>Glucagon: <\/strong>Receptors in the pancreas can sense the decline in blood glucose levels, such as during periods of fasting or during prolonged labour or exercise (Figure 16). In response, the alpha cells of the pancreas secrete the hormone <strong>glucagon<\/strong>, which has several effects:<\/p>\n<ul>\n<li style=\"text-align: justify\">It stimulates the liver to perform <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_414\">glycogenolysis<\/a><\/strong>, the breaking down of glycogen into its component glucose building blocks. The resulting glucose is then released into the circulation for use by body cells.<\/li>\n<li style=\"text-align: justify\">It stimulates gluconeogenesis in the liver, converting amino acids from body proteins into glucose.<\/li>\n<li style=\"text-align: justify\">It stimulates lipolysis, the breakdown of stored triglycerides into free fatty acids and glycerol. Some of the free glycerol released into the bloodstream travels to the liver, which converts it into glucose. This is also a form of gluconeogenesis.<\/li>\n<\/ul>\n<p style=\"text-align: justify\">Taken together, these actions increase blood glucose levels. The activity of glucagon is regulated through a negative feedback mechanism; rising blood glucose levels inhibit further glucagon production and secretion.<\/p>\n<p style=\"text-align: justify\"><strong>Insulin: <\/strong>The primary function of <strong>insulin <\/strong>is to facilitate the uptake of glucose into body cells. Red blood cells, as well as cells of the brain, kidneys, and the lining of the small intestine, do not have insulin receptors on their cell membranes and do not require insulin for glucose uptake. Although all other body cells do require insulin if they are to take glucose from the bloodstream, skeletal muscle cells and adipose cells are the primary targets of insulin.<\/p>\n<p style=\"text-align: justify\">Insulin also reduces blood glucose levels by stimulating glycolysis, the metabolism of glucose for generation of ATP. Moreover, it stimulates the liver to perform <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_415\">glycogenesis<\/a><\/strong>, converting excess glucose into glycogen for storage, and it inhibits enzymes involved in glycogenolysis and gluconeogenesis. Finally, insulin promotes triglyceride and protein synthesis. The secretion of insulin is regulated through a negative feedback mechanism. As blood glucose levels decrease, further insulin release is inhibited.<\/p>\n<p style=\"text-align: justify\"><strong>Hormonal Control of Blood Glucose: <\/strong>The hormonal control of blood glucose\u00a0is\u00a0more\u00a0complex than\u00a0just\u00a0the interaction between insulin and glucagon.\u00a0 Along with glucagon, the\u00a0following\u00a0hormones are called \u201ccounterregulatory\u201d hormones, because\u00a0their effects on glucose levels\u00a0are opposite to\u00a0that of insulin, i.e.,\u00a0they\u00a0all act\u00a0to\u00a0increase\u00a0the level of glucose in the blood:<\/p>\n<ul>\n<li style=\"text-align: justify\"><strong>Epinephrine<\/strong> stimulates the breakdown of glycogen in the liver and muscle (glycogenolysis)<\/li>\n<li style=\"text-align: justify\"><strong>Growth hormone<\/strong>\u00a0stimulates the mobilization and breakdown of fats,\u00a0and decreases\u00a0the uptake of glucose by fat cells<\/li>\n<li style=\"text-align: justify\"><strong>Cortisol\u00a0<\/strong>stimulates the breakdown of proteins and their use in the production of glucose (gluconeogenesis)<\/li>\n<\/ul>\n<figure style=\"width: 610px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311094thed\/wp-content\/uploads\/sites\/1536\/2021\/10\/image23.png\" alt=\"image\" width=\"610\" height=\"855\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 16. Homeostatic Regulation of Blood Glucose Levels.<\/strong> Blood glucose concentration is tightly maintained between 70 mg\/dL and 110 mg\/dL. If blood glucose concentration rises above this range, insulin is released, which stimulates body cells to remove glucose from the blood. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"1-2f\"><\/a>The endocrine functions of the ovaries and testes<\/strong><\/h5>\n<p style=\"text-align: justify\">The <strong>ovaries<\/strong> produce two hormones: estrogens and progesterone. <strong>Estrogens<\/strong> are produced by ovarian follicles. Estrogens stimulate the growth of both primary and secondary sex characteristics. Primary sex characteristics in the female include the growth of the uterus and vagina, and the secondary characteristics include the development of body hair, enlarged breasts and a wider pelvis.<\/p>\n<p style=\"text-align: justify\"><strong>Progesterone<\/strong> is produced by the corpus luteum. It stimulates the development of milk-secretory tissue in the breasts, prepares the uterine lining for the implantation of a fertilized oocyte, and helps to maintain pregnancy.<\/p>\n<p style=\"text-align: justify\">The <strong>testes<\/strong> in the male produce the hormone <strong>testosterone<\/strong>. This hormone stimulates the development of primary sex characteristics, such as the accessory glands and the penis, and secondary sex characteristics such as body hair and a deepening of the voice.<\/p>\n<h5><strong><a id=\"1-2g\"><\/a>The endocrine functions of the stomach and the duodenum<\/strong><\/h5>\n<p style=\"text-align: justify\">The principal function of the <strong>stomach <\/strong>is, of course, digestion. We are most familiar with the capacity of the stomach to store food, and its role in the mechanical and chemical digestion of food. However, there is also some endocrine tissue in the stomach. The secretion of hydrochloric acid in the stomach, and some enzymes, is under the control of a hormone called <strong>gastrin<\/strong>, which is produced by glandular tissue in the wall of the stomach. This hormone is produced by the stomach, travels through the bloodstream, and stimulates the exocrine tissue of the stomach.<\/p>\n<p style=\"text-align: justify\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_416\">duodenum <\/a> <\/strong>also has glandular tissue in its walls. One of the hormones it produces is called <strong>secretin. <\/strong>Secretin travels through the blood and stimulates the pancreas to produce pancreatic juice, which then enters the duodenum and aids in digestion.<\/p>\n<h5><strong><a id=\"1-2h\"><\/a>Thymus and the pineal gland<\/strong><\/h5>\n<p style=\"text-align: justify\">The <strong>thymus gland <\/strong>was once thought to be a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_39_417\">vestigial <\/a> organ. However, it has been determined that it is a central gland of the lymphatic system, which is involved in the body\u2019s immune system. As part of this activity, the gland produces a hormone called <strong>thymosin<\/strong>, which is involved in the maturation and development of the immune system. This gland is larger in infants and decreases in size through adulthood. As a result of the change in size of the gland, the amounts of thymosin produced similarly decrease throughout adulthood.<\/p>\n<p style=\"text-align: justify\">The <strong>pineal gland<\/strong>, situated in the brain, produces the hormone <strong>melatonin<\/strong>. The pineal gland is an interesting structure, because it is responsive to light and may be involved in the seasonal behaviour changes by some animals in response to changes in day length. This hormone also acts on the hypothalamus inhibiting the release of luteinizing hormone, thus affecting the activity of the gonads.<\/p>\n<h5><strong><a id=\"1-2i\"><\/a>Special nature of the prostaglandins<\/strong><\/h5>\n<p style=\"text-align: justify\">Prostaglandins are lipids, much like some hormones. However, they are not produced in special organs or glands, but rather by many cell types from lipids in their own plasma membranes. They usually do not travel long distances within the body, but typically have effects on the tissue where they are produced.<\/p>\n<p style=\"text-align: justify\">The effects of prostaglandins are numerous, including the regulation of blood pressure, regulation of stomach secretions, stimulation and inhibition of uterine contractions, and the transmission of nerve impulses. At least 15 different prostaglandins have been discovered so far. They are vital for the normal functioning of the body. Prostaglandins were originally discovered in the secretions of the prostate gland, from which they got their name.<\/p>\n<h2><a id=\"1-3\"><\/a>Part 3: Summary of Glands, Hormones, their Stimuli, Targets, and Effects<\/h2>\n<table style=\"border-collapse: collapse;width: 100%;height: 1105px\">\n<caption>Table 3: Summary of Glands, Hormones, their Stimuli, Targets, and Effects.<\/caption>\n<thead>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><strong>Organ\/Gland<\/strong><\/td>\n<td style=\"width: 9.97641%;height: 15px\"><strong>Hormone<\/strong><\/td>\n<td style=\"width: 24.2578%;height: 15px\"><strong>Stimuli<\/strong><\/td>\n<td style=\"width: 18.0824%;height: 15px\"><strong>Target<\/strong><\/td>\n<td style=\"width: 19.112%;height: 15px\"><strong>Function\/Effects<\/strong><\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>Disorders<\/strong><\/td>\n<\/tr>\n<\/thead>\n<tbody>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\">Hypothalamus<\/td>\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">[Adreno]corticotropic Releasing Hormone (ACTHRH\/CRH)<\/td>\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Nervous impulse<\/li>\n<li><span style=\"font-family: inherit;font-size: inherit\">Cortisol (negative feedback mechanism)<\/span><\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Adrenocorticotropic hormone (ACTH)<\/td>\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Adrenal glands<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Thyroid stimulating hormone releasing\u00a0 hormone (TRH)<\/td>\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Nervous impulse<\/li>\n<li><span style=\"font-family: inherit;font-size: inherit\">Thyroxin (negative feedback mechanism)<\/span><\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Thyroid Stimulating hormone (TSH)<\/td>\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Thyroid glands<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Gonadotropin releasing hormone (GnRH)<\/td>\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Nervous impulse<\/li>\n<li>Testosterone\/Estrogens (negative feedback <span style=\"font-family: inherit;font-size: inherit\">mechanism<\/span>)<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Luteinizing hormone<\/p>\n<p>\u21d1 Follicle Stimulating hormone (FSH)<\/td>\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Ovaries and Testes<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Growth hormone releasing hormone (GHRH)<\/td>\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Nervous impulse<\/li>\n<li><span style=\"font-family: inherit;font-size: inherit\">Growth hormone (negative feedback mechanism)<\/span><\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Growth hormone (GH)<\/td>\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Pituitary<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Prolactin releasing hormone (PRH)<\/td>\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Nervous impulse<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 Prolactin (PRL)<\/td>\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Pituitary<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Prolactin inhibiting hormone (PIH)<\/td>\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Nervous impulse<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Anterior Pituitary gland [Hypophysis]<\/td>\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d3 Prolactin (PRL)<\/td>\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Pituitary<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Oxytocin<\/p>\n<p><em><span style=\"font-family: inherit;font-size: inherit\">(produced by the hypothalamus and released from the posterior pituitary)<\/span><\/em><\/td>\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">Nervous impulse in response to cervical\/uterine stretching<\/td>\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Uterus<\/li>\n<li>Breast<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">Target\u00a0 uterus:<\/p>\n<ul>\n<li>Contraction of the uterus during childbirth<\/li>\n<li>Induce labor<\/li>\n<\/ul>\n<p>Target breast:<\/p>\n<ul>\n<li>Release of milk during breastfeeding<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">Unknown<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Antidiuretic hormone<\/p>\n<p><em style=\"font-family: inherit;font-size: inherit\">(produced by the hypothalamus and released from the posterior pituitary)<\/em><\/td>\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">Nervous impulse in response to \u21d1 blood osmolarity or \u21d3<span style=\"font-family: inherit;font-size: inherit\">\u00a0blood volume<\/span><\/td>\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Kidney (DCT, Collecting duct)<\/td>\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 water reabsorption<\/td>\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\"><strong>Hyposecretion<\/strong>: Diabetes insipidus<\/p>\n<p><strong>Hypersecretion<\/strong>: Syndrome of inappropriate ADH secretion<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\">Pituitary gland [Hypophysis]<\/td>\n<td style=\"width: 9.97641%;height: 15px;text-align: left;vertical-align: middle\">Adrenocorticotropic hormone (ACTH)<\/td>\n<td style=\"width: 24.2578%;height: 15px;text-align: left;vertical-align: middle\">ACTHRH\/CRH<\/td>\n<td style=\"width: 18.0824%;height: 15px;text-align: left;vertical-align: middle\">Adrenal glands<\/td>\n<td style=\"width: 19.112%;height: 15px;text-align: left;vertical-align: middle\">\u21d1 cortisol<\/p>\n<p>\u21d1 testosterone<\/p>\n<p>\u21d1 aldosterone<\/td>\n<td style=\"width: 18.4042%;height: 15px;text-align: left;vertical-align: middle\">see Adrenal glands<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Thyroid Stimulating hormone (TSH)<\/td>\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">TRH<\/td>\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: middle\">Thyroid gland<\/td>\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">\u21d1 Thyroxin<\/td>\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\">see Thyroid gland<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Luteinizing hormone (LH)<\/td>\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">GnRH<\/td>\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Ovaries<\/li>\n<li>Testes<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">Target ovaries:<\/p>\n<ul>\n<li>\u21d1 Estrogens<\/li>\n<li>\u21d1 Progesterone<\/li>\n<\/ul>\n<p>Target testes:<\/p>\n<ul>\n<li>\u21d1 testosterone<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\">see Ovaries and Testes<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Follicle Stimulating hormone (FSH)<\/td>\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">GnRH<\/td>\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Ovaries<\/li>\n<li>Testes<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">Target ovaries:<\/p>\n<ul>\n<li>\u21d1 Estrogens<\/li>\n<li>\u21d1 Progesterone<\/li>\n<\/ul>\n<p>Target testes:<\/p>\n<ul>\n<li>\u21d1 testosterone<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\">see Ovaries and Testes<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Growth hormone (GH)<\/td>\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">GHRH<\/td>\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: middle\">Liver, muscle, cartilage, bones, several other organs<\/td>\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">\n<ul>\n<li>Growth<\/li>\n<li>\u21d1 protein synthesis<\/li>\n<li>\u21d1 breakdown of fats<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\"><strong>Hyposecretion: <\/strong><\/p>\n<ul>\n<li>Dwarfism in children<\/li>\n<li>Simmond\u2019s disease in adults<\/li>\n<\/ul>\n<p><strong>Hypersecretion:<\/strong><\/p>\n<ul>\n<li>Gigantism in children<\/li>\n<li>Acromegaly in adults<\/li>\n<\/ul>\n<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\n<td style=\"width: 9.97641%;height: 29px;text-align: left;vertical-align: middle\">Prolactin (PRL)<\/td>\n<td style=\"width: 24.2578%;height: 29px;text-align: left;vertical-align: middle\">Prolactin releasing hormone (PRH)<\/td>\n<td style=\"width: 18.0824%;height: 29px;text-align: left;vertical-align: top\">Mammary glands<\/td>\n<td style=\"width: 19.112%;height: 29px;text-align: left;vertical-align: middle\">\u21d1 milk production<\/td>\n<td style=\"width: 18.4042%;height: 29px;text-align: left;vertical-align: middle\">Unknown<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 10.1674%;height: 29px\">Thyroid<\/td>\n<td style=\"width: 9.97641%;height: 29px\">Thyroid hormones<\/td>\n<td style=\"width: 24.2578%;height: 29px\">TSH<\/td>\n<td style=\"width: 18.0824%;height: 29px\">Most cells<\/td>\n<td style=\"width: 19.112%;height: 29px\">\n<ul>\n<li>\u21d1 protein synthesis<\/li>\n<li>\u21d1 breakdown of fats<\/li>\n<li>\u21d1 breakdown of carbs<\/li>\n<li>\u21d1 synthesis of Na+\/K+ pumps<\/li>\n<li>regulates the development of nervous &amp; skeletal systems<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 29px\"><strong>Hyposecretion<\/strong><\/p>\n<ul>\n<li>Cretinism in children<\/li>\n<li>Myxedema in adults<\/li>\n<\/ul>\n<p><strong>Hypersecretion<\/strong><\/p>\n<ul>\n<li>Grave\u2019s disease<\/li>\n<\/ul>\n<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 10.1674%;height: 29px\"><\/td>\n<td style=\"width: 9.97641%;height: 29px\">Calcitonin<\/td>\n<td style=\"width: 24.2578%;height: 29px\">\u21d1 Ca<sup>2+<\/sup> levels<\/td>\n<td style=\"width: 18.0824%;height: 29px\">Skeleton cells (osteoclasts)<\/td>\n<td style=\"width: 19.112%;height: 29px\">\u21d3 blood Ca<sup>2+<\/sup> levels by inhibiting bone resorption and the release of Ca<sup>2+<\/sup> and stimulating Ca<sup>2+<\/sup> uptake and incorporation into the bone matrix<\/td>\n<td style=\"width: 18.4042%;height: 29px\">Very rare<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 10.1674%;height: 29px\">Parathyroid<\/td>\n<td style=\"width: 9.97641%;height: 29px\">Parathyroid hormone<\/td>\n<td style=\"width: 24.2578%;height: 29px\">\u21d3 Ca<sup>2+<\/sup> levels<\/td>\n<td style=\"width: 18.0824%;height: 29px\">Skeleton cells (osteoclasts), kidney and intestine<\/td>\n<td style=\"width: 19.112%;height: 29px\">\u21d1 blood Ca<sup>2+<\/sup> levels<\/td>\n<td style=\"width: 18.4042%;height: 29px\"><strong>Hyposecretion<\/strong><\/p>\n<ul>\n<li>Spams, convulsions<\/li>\n<\/ul>\n<p><strong>Hypersecretion<\/strong><\/p>\n<ul>\n<li>\u21d1 Bone softness, weaken skeletal muscles<\/li>\n<li>\u21d1 Kidney stones<\/li>\n<\/ul>\n<\/td>\n<\/tr>\n<tr style=\"height: 171px\">\n<td style=\"width: 10.1674%;height: 171px\">Adrenal glands<\/td>\n<td style=\"width: 9.97641%;height: 171px\">Aldosterone<\/p>\n<p><em>(type of mineralocorticoid)<\/em><\/td>\n<td style=\"width: 24.2578%;height: 171px\">\n<ul>\n<li>\u21d3 blood pressure<\/li>\n<li>\u21d3 Na+<\/li>\n<li>\u21d1 K+<\/li>\n<li>\u21d1 renin-angiotensin<\/li>\n<li>\u21d1 ACTH<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 171px\">Kidney cells<\/td>\n<td style=\"width: 19.112%;height: 171px\">\u21d1 Na<sup>+<\/sup> reabsorption<\/p>\n<p>\u21d1 excretion of K<sup>+<\/sup>, H<sup>+<\/sup><\/td>\n<td style=\"width: 18.4042%;height: 171px\"><strong>Hyposecretion<\/strong><\/p>\n<ul>\n<li>Addison\u2019s disease<\/li>\n<\/ul>\n<p><strong>Hypersecretion<\/strong><\/p>\n<ul>\n<li>Aldosteronism<\/li>\n<\/ul>\n<p><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 156px\">\n<td style=\"width: 10.1674%;height: 156px\"><\/td>\n<td style=\"width: 9.97641%;height: 156px\">Cortisol<\/p>\n<p><em>(type of glucocorticoid)<\/em><\/td>\n<td style=\"width: 24.2578%;height: 156px\">\n<ul>\n<li>\u21d3 ACTH<\/li>\n<li>Stress<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 156px\">Most body cells<\/td>\n<td style=\"width: 19.112%;height: 156px\">\u21d1 Muscle metabolism<\/p>\n<p>\u21d1 glucose blood levels<\/p>\n<p>\u21d1 blood pressure (vasoconstriction)<\/td>\n<td style=\"width: 18.4042%;height: 156px\"><strong>Hyposecretion<\/strong><\/p>\n<ul>\n<li>Addison\u2019s disease<\/li>\n<\/ul>\n<p><strong>Hypersecretion<\/strong><\/p>\n<ul>\n<li>Cushing\u2019s disease<strong><br \/>\n<\/strong><\/li>\n<\/ul>\n<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 10.1674%;height: 32px\"><\/td>\n<td style=\"width: 9.97641%;height: 32px\">Testosterone <em>(in small amounts)<\/em><\/td>\n<td style=\"width: 24.2578%;height: 32px\"><\/td>\n<td style=\"width: 18.0824%;height: 32px\">Various body cells<\/td>\n<td style=\"width: 19.112%;height: 32px\">Development of secondary sex characteristics<\/td>\n<td style=\"width: 18.4042%;height: 32px\"><strong>Hypersecretion<\/strong><\/p>\n<ul>\n<li>Masculinization of females<\/li>\n<\/ul>\n<\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px\">Epinephrine (adrenaline)<\/td>\n<td style=\"width: 24.2578%;height: 15px\">Stress<\/td>\n<td style=\"width: 18.0824%;height: 15px\">Many body cells<\/td>\n<td style=\"width: 19.112%;height: 15px\">\n<ul>\n<li>\u21d1 blood pressure (vasoconstriction)<\/li>\n<li>\u21d1 blood flow to heart and muscles<\/li>\n<li>\u21d1 bronchial dilatation<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px\">Norepinephrine (noradrenaline)<\/td>\n<td style=\"width: 24.2578%;height: 15px\">Stress<\/td>\n<td style=\"width: 18.0824%;height: 15px\">Many body cells<\/td>\n<td style=\"width: 19.112%;height: 15px\">\n<ul>\n<li>\u21d1 blood pressure (vasoconstriction)<\/li>\n<li>\u21d3 blood flow to gut &amp; skins<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px\">Estrogens<\/td>\n<td style=\"width: 24.2578%;height: 15px\">\n<ul>\n<li>Luteinizing hormone (LH)<\/li>\n<li>Follicle Stimulating hormone (FSH)<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px\">\n<ul>\n<li>Uterus<\/li>\n<li>Vagina<\/li>\n<li>Several body cells<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 19.112%;height: 15px\">Development of primary and secondary sex characteristics (body hair, breasts, pelvis)<\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\"><\/td>\n<td style=\"width: 9.97641%;height: 15px\">Progesterone<\/td>\n<td style=\"width: 24.2578%;height: 15px\">\n<ul>\n<li>Luteinizing hormone (LH)<\/li>\n<li>Follicle Stimulating hormone (FSH)<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px\">\n<ul>\n<li>Uterus<\/li>\n<li>Vagina<\/li>\n<li>Several body cells<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 19.112%;height: 15px\">Development of primary and secondary sex characteristics (body hair, breasts, pelvis)<\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\">Testis<\/td>\n<td style=\"width: 9.97641%;height: 15px\">Testosterone<\/td>\n<td style=\"width: 24.2578%;height: 15px\">\n<ul>\n<li>Luteinizing hormone (LH)<\/li>\n<li>Follicle Stimulating hormone (FSH)<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px\">\n<ul>\n<li>Penis<\/li>\n<li>Several body cells<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 19.112%;height: 15px\">Development of primary and secondary sex characteristics (body hair, voice change)<\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\">Thymus<\/td>\n<td style=\"width: 9.97641%;height: 15px\">Thymosin<\/td>\n<td style=\"width: 24.2578%;height: 15px\">\n<ul>\n<li>Prolactin<\/li>\n<li>Thyroid<\/li>\n<li>Adrenal hormones<\/li>\n<li>Gonads<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.0824%;height: 15px\">Immune system<\/td>\n<td style=\"width: 19.112%;height: 15px\">Development of the immune system<\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\">Pineal gland<\/td>\n<td style=\"width: 9.97641%;height: 15px\">Melatonin<\/td>\n<td style=\"width: 24.2578%;height: 15px\">Light<\/td>\n<td style=\"width: 18.0824%;height: 15px\">Hypothalamus<\/td>\n<td style=\"width: 19.112%;height: 15px\">Regulation of daily circadian rhythm<\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\">Body Tissues<\/td>\n<td style=\"width: 9.97641%;height: 15px\">Prostaglandins<\/td>\n<td style=\"width: 24.2578%;height: 15px\">\u2018Local homeostatic imbalance\u2019<\/td>\n<td style=\"width: 18.0824%;height: 15px\">Several body cells<\/td>\n<td style=\"width: 19.112%;height: 15px\">\n<ul>\n<li>Regulation of blood pressure<\/li>\n<li>Stomach secretions<\/li>\n<li>Immune response<\/li>\n<li>Clotting<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 15px\">\n<td style=\"width: 10.1674%;height: 15px\">Pancreas (Islets of Langerhans)<\/td>\n<td style=\"width: 9.97641%;height: 15px\">Glucagon (alpha cells)<\/td>\n<td style=\"width: 24.2578%;height: 15px\">\u21d3 Blood glucose levels<\/td>\n<td style=\"width: 18.0824%;height: 15px\">Liver and other organs\/tissues<\/td>\n<td style=\"width: 19.112%;height: 15px\">\u21d1 Blood glucose levels by:<\/p>\n<ul>\n<li>\u21d1 gluconeogenesis,<\/li>\n<li>\u21d1 glycogen breakdown,<\/li>\n<li>\u21d1 triglycerides breakdown<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 15px\"><strong>\u00a0<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 171px\">\n<td style=\"width: 10.1674%;height: 171px\"><\/td>\n<td style=\"width: 9.97641%;height: 171px\">Insulin (beta cells)<\/td>\n<td style=\"width: 24.2578%;height: 171px\">\u21d1 Blood glucose levels<\/td>\n<td style=\"width: 18.0824%;height: 171px\">Liver and other organs\/tissues<\/td>\n<td style=\"width: 19.112%;height: 171px\">\u21d3 Blood glucose levels by:<\/p>\n<ul>\n<li>\u21d1 cell glucose uptake,<\/li>\n<li>\u21d1 glycogen synthesis,<\/li>\n<li>\u21d1 fatty acid synthesis<\/li>\n<\/ul>\n<\/td>\n<td style=\"width: 18.4042%;height: 171px\"><strong>Hyposecretion<\/strong><\/p>\n<ul>\n<li>Diabetes mellitus<\/li>\n<\/ul>\n<p><strong>Hypersecretion<\/strong><\/p>\n<ul>\n<li>Hyperinsulinism<\/li>\n<\/ul>\n<p>&nbsp;<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><a id=\"P\"><\/a>Practice Questions<\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p style=\"text-align: justify\"><strong>Part 1:<\/strong> General properties of the endocrine system<\/p>\n<div id=\"h5p-72\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-72\" class=\"h5p-iframe\" data-content-id=\"72\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"1-1\"><\/iframe><\/div>\n<\/div>\n<p><strong>Part 2:<\/strong> Major endocrine organs and their secretions<\/p>\n<div id=\"h5p-73\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-73\" class=\"h5p-iframe\" data-content-id=\"73\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"1-2\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-74\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-74\" class=\"h5p-iframe\" data-content-id=\"74\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"1-3\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-75\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-75\" class=\"h5p-iframe\" data-content-id=\"75\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"1-4\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-76\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-76\" class=\"h5p-iframe\" data-content-id=\"76\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"1-5\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-77\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-77\" class=\"h5p-iframe\" data-content-id=\"77\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"1-5\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-78\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-78\" class=\"h5p-iframe\" data-content-id=\"78\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"1-6\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-79\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-79\" class=\"h5p-iframe\" data-content-id=\"79\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"1-10\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-80\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-80\" class=\"h5p-iframe\" data-content-id=\"80\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"1-11\"><\/iframe><\/div>\n<\/div>\n<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_39_464\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_464\"><div tabindex=\"-1\"><p>Molecule (usually a protein) that catalyzes chemical reactions.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_465\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_465\"><div tabindex=\"-1\"><p>Haploid reproductive cell (egg or sperm in humans) that contributes genetic material to form an offspring.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_460\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_460\"><div tabindex=\"-1\"><p>Secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_459\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_459\"><div tabindex=\"-1\"><p>Gland that secretes substance directly to target tissues or outside of body via glandular ducts (e.g. sweat glands, digestive glands).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_458\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_458\"><div tabindex=\"-1\"><p>Tissue or organ that secretes hormones into the blood and lymph without ducts such that they may be transported to organs distant from the site of secretion.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_391\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_391\"><div tabindex=\"-1\"><p>Bean-sized organ suspended from the hypothalamus that produces, stores, and secretes hormones in response to hypothalamic stimulation (also called hypophysis).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_471\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_471\"><div tabindex=\"-1\"><p>Hypothalamic hormone stored in the posterior pituitary gland and important in stimulating uterine contractions in labor, milk ejection during breastfeeding, and feelings of attachment (also produced in males).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_409\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_409\"><div tabindex=\"-1\"><p>Sensory receptor that is stimulated by changes in solute concentration (osmotic pressure) in the blood.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_392\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_392\"><div tabindex=\"-1\"><p>Region of the diencephalon inferior to the thalamus that functions in neural and endocrine signaling.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_410\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_410\"><div tabindex=\"-1\"><p>The solute concentration of a solution.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_412\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_412\"><div tabindex=\"-1\"><p>Hormones produced by the zona fasciculata of the adrenal cortex that influence glucose metabolism.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_446\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_446\"><div tabindex=\"-1\"><p>Endocrine gland located at the top of each kidney that is important for the regulation of the stress response, blood pressure and blood volume, water homeostasis, and electrolyte levels.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_447\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_447\"><div tabindex=\"-1\"><p>Building block of proteins; characterized by an amino and carboxyl functional groups and a variable side-chain.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_448\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_448\"><div tabindex=\"-1\"><p>A type of lipid containing four rings and a fatty acid tail. Examples include testosterone and cholesterol.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_469\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_469\"><div tabindex=\"-1\"><p>Describes a substance or structure repelled by water.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_472\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_472\"><div tabindex=\"-1\"><p>Hormone produced by the adrenal gland in response to stress, stimulates gluconeogenesis, the catabolism of glycogen, and downregulation of the immune system and glucose levels.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_449\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_449\"><div tabindex=\"-1\"><p>Primary and most potent catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called adrenaline.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_389\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_389\"><div tabindex=\"-1\"><p>Protein within a cell or on the cell membrane that binds a hormone, initiating the target cell response.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_450\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_450\"><div tabindex=\"-1\"><p>Large butterfly-shaped endocrine gland responsible for the synthesis of thyroid hormones. Located anterior to the trachea, just inferior to the larynx.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_468\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_468\"><div tabindex=\"-1\"><p>Describes a substance or structure attracted to water.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_451\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_451\"><div tabindex=\"-1\"><p>Pancreatic hormone that stimulates the catabolism of glycogen to glucose, thereby increasing blood glucose levels.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_452\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_452\"><div tabindex=\"-1\"><p>Steady, dynamic state of body systems (specifically of extracellular fluid) that living organisms maintain.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_454\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_454\"><div tabindex=\"-1\"><p>Secondary catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called noradrenaline.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_453\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_453\"><div tabindex=\"-1\"><p>Chemical signal that is released from the synaptic end bulb of a neuron to cause a change in the target cell.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_390\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_390\"><div tabindex=\"-1\"><p>A general anatomical term for a funnel-shaped structure; in the hypothalamus, the stalk containing vasculature and neural tissue that connects the pituitary gland to the hypothalamus (also called the pituitary stalk).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_393\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_393\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_1250\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_1250\"><div tabindex=\"-1\"><p>(Also corticotropin releasing hormone, CRH) hormone from the hypothalamus that stimulates adrenocorticotropic hormone release from the anterior pituitary.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_1249\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_1249\"><div tabindex=\"-1\"><p>Hormone from the hypothalamus that stimulates release of thyroid stimulating hormone from the anterior pituitary.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_1248\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_1248\"><div tabindex=\"-1\"><p>Hormone from the hypothalamus that stimulates release of growth hormone (GH) from the anterior pituitary.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_1247\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_1247\"><div tabindex=\"-1\"><p>Hormone released by the hypothalamus that stimulates the release of\u00a0hormones known as gonadotropins from the anterior pituitary: follicle stimulating hormone (FSH) and luteinizing hormone (LH)<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_473\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_473\"><div tabindex=\"-1\"><p>(Also, vasopressin) hypothalamic hormone that is stored by the posterior pituitary and that signals the kidneys to reabsorb water.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_474\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_474\"><div tabindex=\"-1\"><p>(Also, somatotropin) anterior pituitary hormone that promotes tissue building and influences nutrient metabolism.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_475\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_475\"><div tabindex=\"-1\"><p>Anterior pituitary hormone that promotes development of the mammary glands and the production of breast milk. Often abbreviated PRL<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_476\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_476\"><div tabindex=\"-1\"><p>Anterior pituitary hormone that triggers secretion of thyroid hormones by the thyroid gland (often abbreviated TSH, also called thyrotropin)<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_1374\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_1374\"><div tabindex=\"-1\"><p>(Also, corticotropin) anterior pituitary hormone that stimulates the adrenal cortex to secrete corticosteroid hormones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_478\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_478\"><div tabindex=\"-1\"><p>Anterior pituitary hormone that stimulates the production and maturation of sex cells.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_479\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_479\"><div tabindex=\"-1\"><p>Anterior pituitary hormone that triggers ovulation and the production of ovarian hormones in females, and the production of testosterone in males.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_408\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_408\"><div tabindex=\"-1\"><p>Hormones that affect the secretion of other hormones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_480\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_480\"><div tabindex=\"-1\"><p>Hormones that regulate the function of the gonads.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_394\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_394\"><div tabindex=\"-1\"><p>Hormones that regulate the function of the gonads.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_481\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_481\"><div tabindex=\"-1\"><p>Class of predominantly female sex hormones important for the development and growth of the female reproductive tract, secondary sex characteristics, the female reproductive cycle, and the maintenance of pregnancy. Estradiol is the most common active estrogen.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_482\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_482\"><div tabindex=\"-1\"><p>Predominantly female sex hormone important in regulating the female reproductive cycle and the maintenance of pregnancy.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_483\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_483\"><div tabindex=\"-1\"><p>Female gonads that produce oocytes and sex steroid hormones (notably estrogen and progesterone).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_485\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_485\"><div tabindex=\"-1\"><p>Steroid hormone secreted by the male testes and important in the maturation of sperm cells, growth and development of the male reproductive system, and the development of male secondary sex characteristics.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_484\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_484\"><div tabindex=\"-1\"><p>Male gonad (plural = testes).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_486\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_486\"><div tabindex=\"-1\"><p>(In nervous system) a localized collection of neuron cell bodies that are functionally related; a \u201ccenter\u201d of neural function (plural= nuclei).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_487\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_487\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_395\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_395\"><div tabindex=\"-1\"><p>Enlargement of the thyroid gland either as a result of iodine deficiency or hyperthyroidism.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_411\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_411\"><div tabindex=\"-1\"><p>Hormones produced by the zona glomerulosa cells of the adrenal cortex that influence fluid and electrolyte balance.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_396\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_396\"><div tabindex=\"-1\"><p>Process of glucose synthesis from pyruvate or other molecules.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_414\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_414\"><div tabindex=\"-1\"><p>Metabolic process that breaks down glycogen into glucose molecules.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_415\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_415\"><div tabindex=\"-1\"><p>Metabolic process that builds glycogen molecules from glucose.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_416\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_416\"><div tabindex=\"-1\"><p>First part of the small intestine, which starts at the pyloric sphincter and ends at the jejunum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_39_417\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_39_417\"><div tabindex=\"-1\"><p>A structure that, through the course of evolution, no longer has a function.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":1440,"menu_order":1,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-39","chapter","type-chapter","status-publish","hentry"],"part":18,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/pressbooks\/v2\/chapters\/39","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/wp\/v2\/users\/1440"}],"version-history":[{"count":25,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/pressbooks\/v2\/chapters\/39\/revisions"}],"predecessor-version":[{"id":1599,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/pressbooks\/v2\/chapters\/39\/revisions\/1599"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/pressbooks\/v2\/parts\/18"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/pressbooks\/v2\/chapters\/39\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/wp\/v2\/media?parent=39"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/pressbooks\/v2\/chapter-type?post=39"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/wp\/v2\/contributor?post=39"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol120312094thed\/wp-json\/wp\/v2\/license?post=39"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}