{"id":1322,"date":"2019-07-26T20:53:38","date_gmt":"2019-07-27T00:53:38","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/chapter\/unit-6-tissue-structure-and-functions\/"},"modified":"2024-04-25T01:08:09","modified_gmt":"2024-04-25T05:08:09","slug":"unit-6-tissue-structure-and-functions","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/chapter\/unit-6-tissue-structure-and-functions\/","title":{"raw":"Unit 6: Tissue Structure and Functions","rendered":"Unit 6: Tissue Structure and Functions"},"content":{"raw":"<div class=\"unit-6:-tissue-structure-and-functions-\">\r\n<div class=\"textbox shaded\">\r\n\r\n<strong>Unit outline<\/strong>\r\n\r\n<a href=\"#6.1\"><strong>Part 1.<\/strong> Tissue: a higher level of organization<\/a>\r\n<ul style=\"margin-top: 1.42857em;margin-bottom: 1.42857em\">\r\n \t<li><a href=\"#6.1a\">The four types of tissues<\/a><\/li>\r\n<\/ul>\r\n<a href=\"#6.2\"><strong>Part 2<\/strong>. Epithelial tissue<\/a>\r\n<ul>\r\n \t<li><a href=\"#6.2a\">General structure of epithelial tissue<\/a><\/li>\r\n \t<li><a href=\"#6.2b\">General functions of epithelial tissue<\/a><\/li>\r\n \t<li><a href=\"#6.2c\">Classification of epithelial tissue<\/a><\/li>\r\n<\/ul>\r\n<a href=\"#6.3\"><strong>Part 3<\/strong>. Connective tissue<\/a>\r\n<ul>\r\n \t<li><a href=\"#6.3a\">General structure of connective tissue<\/a><\/li>\r\n \t<li><a href=\"#6.3b\">Functions of connective tissue<\/a><\/li>\r\n \t<li><a href=\"#6.3c\">Classification of connective tissue<\/a><\/li>\r\n<\/ul>\r\n<a href=\"#6.4\"><strong>Part <\/strong><strong>4<\/strong><strong>.<\/strong> Muscle tissue<\/a>\r\n<ul>\r\n \t<li><a href=\"#6.4a\">Skeletal muscle<\/a><\/li>\r\n \t<li><a href=\"#6.4b\">Cardiac muscle<\/a><\/li>\r\n \t<li><a href=\"#6.4c\">Smooth muscle<\/a><\/li>\r\n<\/ul>\r\n<a href=\"#6.5\"><strong>Part <\/strong><strong>5<\/strong>. Nervous tissue<\/a>\r\n<h4><em><a href=\"#P\"><strong>Practice Questions<\/strong><\/a><\/em><\/h4>\r\n<\/div>\r\n&nbsp;\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\r\n<strong>I<\/strong><strong>. <\/strong>Define tissue and describe the importance of tissue level organization to an organism.\r\n\r\n<strong>II<\/strong><strong>. <\/strong>Describe the structure and function of epithelial, connective, muscle, and nervous tissue.\r\n\r\n<strong>III<\/strong><strong>.<\/strong> Explain the relationships between structure and function of tissues.\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\r\n<strong>I<\/strong><strong>. <\/strong>Define tissue and describe the importance of tissue level organization to an organism.\r\n<ol>\r\n \t<li>What is a tissue?<\/li>\r\n \t<li>What is the main benefit to humans of having tissue level organization?<\/li>\r\n<\/ol>\r\n<strong>II<\/strong><strong>. <\/strong>Describe the structure and function of epithelial, connective, muscle, and nervous tissue.\r\n<ol>\r\n \t<li>Describe the general structure of each of the following:\r\n<ul>\r\n \t<li>Epithelial tissue<\/li>\r\n \t<li>Connective tissue<\/li>\r\n \t<li>Muscle tissue<\/li>\r\n \t<li>Nervous tissue<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>Describe the general function of each of the following:\r\n<ul>\r\n \t<li>Epithelial tissue<\/li>\r\n \t<li>Connective tissue<\/li>\r\n \t<li>Muscle tissue<\/li>\r\n \t<li>Nervous tissue<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>Compare and contrast the structure of the three types of connective tissue (proper, supportive connective tissue, and liquid connective tissue).<\/li>\r\n \t<li>Compare and contrast the structure of the three types of stratified epithelium (stratified squamous epithelium, stratified cuboidal epithelium, and stratified columnar epithelium).<\/li>\r\n<\/ol>\r\n<strong>III<\/strong><strong>.<\/strong> Explain the relationships between structure and function of tissues.\r\n<ol>\r\n \t<li>Use annotated diagrams to describe the structure and function of each of the seven main types of epithelial tissue (including pseudostratified columnar epithelium).<\/li>\r\n \t<li>Compare and contrast the structure and function of:\r\n<ul>\r\n \t<li>Simple squamous epithelium and stratified squamous epithelium<\/li>\r\n \t<li>Simple squamous epithelium and simple columnar epithelium<\/li>\r\n \t<li>Simple squamous epithelium and simple cuboidal epithelium<\/li>\r\n \t<li>Simple cuboidal epithelium and simple columnar epithelium<\/li>\r\n \t<li>Simple cuboidal epithelium and stratified cuboidal epithelium<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>Create a table stating:\r\n<ul>\r\n \t<li>The matrix composition,<\/li>\r\n \t<li>The cellular types,<\/li>\r\n \t<li>The main function(s), and<\/li>\r\n \t<li>Specific examples<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n<p style=\"padding-left: 40px\">...of each of the following types of connective tissue:<\/p>\r\n\r\n<ol>\r\n \t<li style=\"list-style-type: none\">\r\n<ul>\r\n \t<li>Fluid connective tissue<\/li>\r\n \t<li>Loose connective tissue<\/li>\r\n \t<li>Dense connective tissue<\/li>\r\n \t<li>Cartilage<\/li>\r\n \t<li>Bone<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>Compare and contrast the three types of muscle tissue by discussing each of the following characteristics:\r\n<ul>\r\n \t<li>The structure of each of the three types of muscle tissue<\/li>\r\n \t<li>How each type of muscle tissue is controlled (i.e., whether voluntary control is available or not)<\/li>\r\n \t<li>The function(s) of each of the three types of muscle tissue<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>Name and describe both of the two main cell types in the nervous tissue. In your description, include:\r\n<ul>\r\n \t<li>Their general cellular morphology (i.e., their shape)<\/li>\r\n \t<li>Their main function(s)<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>What is the relationship between the structure and the function of the following tissues?\r\n<ul>\r\n \t<li>Simple squamous epithelium<\/li>\r\n \t<li>Stratified squamous epithelium<\/li>\r\n \t<li>Fluid connective tissue<\/li>\r\n \t<li>Loose connective tissue<\/li>\r\n \t<li>Dense connective tissue<\/li>\r\n \t<li>Cartilage<\/li>\r\n \t<li>Bone<\/li>\r\n \t<li>Nervous tissue<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n&nbsp;\r\n<p style=\"text-align: justify\">The body contains at least 200 distinct cell types. These cells contain essentially the same internal structures, yet they vary enormously in shape and function. The different types of cells are not randomly distributed throughout the body; rather they occur in organized layers, a level of organization referred to as tissue.<\/p>\r\n\r\n<h2><strong><a id=\"6.1\"><\/a>Part 1: <\/strong><strong>Tissue: a higher level of organization<\/strong><\/h2>\r\n<p style=\"text-align: justify\">The term <strong>[pb_glossary id=\"2218\"]tissue[\/pb_glossary] <\/strong>is used to describe a group of cells found together in the body. The cells within a tissue share a common embryonic origin. Microscopic observation reveals that the cells in a tissue share morphological features and are arranged in an orderly pattern that achieves the tissue\u2019s functions. From the evolutionary perspective, tissues appear in more complex organisms. For example, multicellular protists, ancient eukaryotes, do not have cells organized into tissues. Having tissue level organization increases the efficiency of the body as different shapes and internal structures are better suited to carry out different functions. Having different tissues for different functions allows for a greater speed of activity and a greater effectiveness in performing the various activities.<\/p>\r\n<p style=\"text-align: justify\">Although there are many types of cells in the human body, they are organized into four broad categories of tissues: [pb_glossary id=\"2239\"]epithelial[\/pb_glossary], [pb_glossary id=\"2194\"]connective[\/pb_glossary], muscle, and nervous. Each of these categories is characterized by specific functions that contribute to the overall health and maintenance of the body. A disruption of the structure is a sign of injury or disease. Such changes can be detected through <strong>[pb_glossary id=\"2279\"]histology[\/pb_glossary]<\/strong>, the microscopic study of tissue appearance, organization, and function.<\/p>\r\n\r\n<h5><strong><a id=\"6.1a\"><\/a>The Four Types of Tissues<\/strong><\/h5>\r\n<p style=\"text-align: justify\">[pb_glossary id=\"2239\"]Epithelial tissue[\/pb_glossary], also referred to as epithelium, refers to the sheets of cells that cover exterior surfaces of the body, lines internal cavities and passageways, and forms certain glands. [pb_glossary id=\"2194\"]Connective tissue[\/pb_glossary], as its name implies, binds the cells and organs of the body together and functions in the protection, support, and integration of all parts of the body. Muscle tissue is excitable, responding to stimulation and contracting to provide movement, and occurs as three major types: skeletal ([pb_glossary id=\"2280\"]voluntary[\/pb_glossary]) muscle, smooth muscle, and cardiac muscle in the heart. Nervous tissue is also excitable, allowing the propagation of electrochemical signals in the form of nerve impulses that communicate between different regions of the body (Figure 1).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"986\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image1-6.png\" alt=\"image\" width=\"986\" height=\"1036\" \/> <strong>Figure 1. Four Types of Tissue: Body.<\/strong> The four types of tissues are exemplified in nervous tissue, stratified squamous epithelial tissue, cardiac muscle tissue, and connective tissue in small intestine. Clockwise from nervous tissue, LM \u00d7 872, LM \u00d7 282, LM \u00d7 460, LM \u00d7 800. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n<p style=\"text-align: justify\">The next level of organization is the organ, where several types of tissues come together to form a working unit. Just as knowing the structure and function of cells helps you in your study of tissues, knowledge of tissues will help you understand how organs function. The epithelial and connective tissues are discussed in detail in this chapter. Muscle and nervous tissues will be discussed only briefly in this section.<\/p>\r\n\r\n<h2><strong><a id=\"6.2\"><\/a>Part 2: <\/strong><strong>Epithelial Tissue<\/strong><\/h2>\r\n<p style=\"text-align: justify\">Most epithelial tissues are essentially large sheets of cells covering all the surfaces of the body exposed to the outside world, and lining the outside of organs and the body cavities. Epithelium also forms much of the glandular tissue of the body. Skin is not the only area of the body exposed to the outside. Other areas include the airways, the digestive tract, as well as the urinary and reproductive systems, all of which are lined by an epithelium. Hollow organs and body cavities that do not connect to the exterior of the body, which includes, blood vessels and serous membranes, are lined by endothelium (plural = endothelia), which is a type of epithelium.<\/p>\r\n\r\n<h5><strong><a id=\"6.2a\"><\/a>General Structure of Epithelial Tissue<\/strong><\/h5>\r\n<p style=\"text-align: justify\">All epithelia share some important structural and functional features. This tissue is highly cellular, with little or no extracellular material present between cells. The epithelial cells exhibit polarity with differences in structure and function between the exposed or <strong>[pb_glossary id=\"2281\"]apical[\/pb_glossary]<\/strong> facing surface of the cell and the <strong>[pb_glossary id=\"2282\"]basal[\/pb_glossary] <\/strong>surface close to the underlying body structures. Particular structures found in some epithelial cells are an adaptation to specific functions. Certain organelles are segregated to the basal sides, whereas other organelles and extensions, such as cilia, when present, are on the apical surface. The <strong>[pb_glossary id=\"2283\"]basal lamina[\/pb_glossary]<\/strong>, a mixture of glycoproteins and collagen, provides an attachment site for the epithelium, separating it from underlying connective tissue. The basal lamina attaches to a <strong>[pb_glossary id=\"2284\"]reticular lamina[\/pb_glossary]<\/strong>, which is secreted by the underlying connective tissue, forming a <strong>[pb_glossary id=\"2285\"]basement membrane[\/pb_glossary]<\/strong> that helps hold it all together.<\/p>\r\n<p style=\"text-align: justify\">Epithelial tissues are nearly completely [pb_glossary id=\"2286\"]avascular[\/pb_glossary]. For instance, no blood vessels cross the basement membrane to enter the tissue, and nutrients must come by diffusion or absorption from underlying tissues or the surface. Many epithelial tissues are capable of rapidly replacing damaged and dead cells. Sloughing off of damaged or dead cells is a characteristic of surface epithelium and allows our airways and digestive tracts to rapidly replace damaged cells with new cells.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"6.2b\"><\/a>General Functions of Epithelial Tissue<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Epithelial tissues provide the body\u2019s first line of protection from physical, chemical, and biological wear and tear. The cells of an epithelium act as gatekeepers of the body controlling permeability and allowing selective transfer of materials across a physical barrier. All substances that enter the body must cross an epithelium. Some epithelia often include structural features that allow the selective transport of molecules and [pb_glossary id=\"2093\"]ions[\/pb_glossary] across their cell membranes.<\/p>\r\n<p style=\"text-align: justify\">Many epithelial cells are capable of secretion and release mucous and specific chemical compounds onto their apical surfaces. The epithelium of the small intestine releases digestive [pb_glossary id=\"2173\"]enzymes[\/pb_glossary], for example. Cells lining the respiratory tract secrete mucous that traps incoming microorganisms and particles. A glandular epithelium contains many secretory cells.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"6.2c\"><\/a>Classification of Epithelial Tissues<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Epithelial tissues are classified according to the shape of the cells and number of the cell layers formed (Figure 2). Cell shapes can be squamous (flattened and thin), cuboidal (boxy, as wide as it is tall), or columnar (rectangular, taller than it is wide). Similarly, the number of cell layers in the tissue can be one\u2014where every cell rests on the basal lamina\u2014which is a simple epithelium, or more than one, which is a stratified epithelium and only the basal layer of cells rests on the basal lamina. Pseudostratified (pseudo- = \u201cfalse\u201d) describes tissue with a single layer of irregularly shaped cells that give the appearance of more than one layer. Transitional describes a form of specialized stratified epithelium in which the shape of the cells can vary.<\/p>\r\n<p style=\"text-align: justify\"><strong>Simple Epithelium:<\/strong> The shape of the cells in the single cell layer of simple epithelium reflects the functioning of those cells. The cells in <strong>[pb_glossary id=\"2287\"]simple squamous epithelium[\/pb_glossary]<\/strong> have the appearance of thin scales. Squamous cell nuclei tend to be flat, horizontal, and elliptical, mirroring the form of the cell. Simple squamous epithelium, because of the thinness of the cell, is present where rapid passage of chemical compounds is observed. The alveoli of lungs where gases diffuse, segments of kidney tubules, and the lining of capillaries are also made of simple squamous epithelial tissue.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1205\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image2-6.png\" alt=\"image\" width=\"1205\" height=\"969\" \/> <strong>Figure 2. Types of Epithelial Tissue.<\/strong> Simple epithelial tissue is organized as a single layer of cells and stratified epithelial tissue is formed by several layers of cells. Pseudostratified epithelial tissue is a single layer of cells that appear to be multiple layers because of the position of their nuclei. Epithelial tissue is further defined by the shape of the apical layer of cells in the tissue.[\/caption]\r\n<p style=\"text-align: justify\">In <strong>[pb_glossary id=\"2288\"]simple cuboidal epithelium[\/pb_glossary]<\/strong>, the nucleus of the box-like cells appears round and is generally located near the center of the cell. These epithelia are active in the secretion and absorptions of molecules. Simple cuboidal epithelia are observed in the lining of the kidney tubules and in the ducts of glands (Figure 3).<\/p>\r\n<p style=\"text-align: justify\">In <strong>[pb_glossary id=\"2289\"]simple columnar epithelium[\/pb_glossary]<\/strong>, the nucleus of the tall column-like cells tends to be elongated and located in the basal end of the cells (Figure 3). Like the cuboidal epithelia, this epithelium is active in the absorption and secretion of molecules. Simple columnar epithelium forms the lining of some sections of the digestive system and parts of the female reproductive tract. Ciliated columnar epithelium is composed of simple columnar epithelial cells with [pb_glossary id=\"2291\"]cilia[\/pb_glossary] on their [pb_glossary id=\"2281\"]apical[\/pb_glossary] surfaces. These epithelial cells are found in the lining of the [pb_glossary id=\"2292\"]uterine tubes[\/pb_glossary] and parts of the respiratory system, where the beating of the cilia helps remove particulate matter.<\/p>\r\n<p style=\"text-align: justify\"><strong>[pb_glossary id=\"2290\"]Pseudostratified columnar epithelium[\/pb_glossary]<\/strong> is a type of epithelium that appears to be stratified but instead consists of a single layer of irregularly shaped and differently sized columnar cells. In pseudostratified epithelium, nuclei of neighbouring cells appear at different levels rather than clustered in the [pb_glossary id=\"2282\"]basal[\/pb_glossary] end (Figure 3). The arrangement gives the appearance of stratification; but in fact, all the cells are in contact with the basal lamina, although some do not reach the [pb_glossary id=\"2281\"]apical[\/pb_glossary] surface. Pseudostratified columnar epithelium is found in the respiratory tract, where some of these cells have cilia.<\/p>\r\n<p style=\"text-align: justify\"><strong>Stratified Epithelium:<\/strong> A stratified epithelium consists of several stacked layers of cells. This epithelium protects against physical and chemical wear and tear. The stratified epithelium is named by the shape of the most apical layer of cells, closest to the free space<strong>. <\/strong><\/p>\r\n<p style=\"text-align: justify\"><strong>[pb_glossary id=\"2293\"]Stratified squamous epithelium[\/pb_glossary]<\/strong> is the most common type of stratified epithelium in the human body. The apical cells are squamous, whereas the basal layer contains either columnar or cuboidal cells. The top layer may be covered with dead cells filled with [pb_glossary id=\"2294\"]keratin[\/pb_glossary]. Mammalian skin is an example of this dry, keratinized, stratified squamous epithelium. The lining of the mouth cavity is an example of an nonkeratinized, stratified squamous epithelium. <strong>[pb_glossary id=\"2295\"]Stratified cuboidal epithelium[\/pb_glossary]<\/strong> and<strong> [pb_glossary id=\"2296\"]stratified columnar epithelium[\/pb_glossary]<\/strong> can also be found in certain glands and ducts, but are uncommon in the human body (Figure 3).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"652\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image3-6.png\" alt=\"image\" width=\"652\" height=\"1045\" \/> <strong>Figure 3. Summary of Epithelial Tissue Types.<\/strong> Different types of epithelial tissue serve different functions and are found in different locations in the body.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"131\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image4-6.png\" alt=\"image\" width=\"131\" height=\"133\" \/> Watch <a href=\"https:\/\/youtu.be\/lUe_RI_m-Vg\">this CrashCourse video<\/a> to learn more about epithelial histology. Direct link:\u00a0<a href=\"https:\/\/youtu.be\/lUe_RI_m-Vg\">https:\/\/youtu.be\/lUe_RI_m-Vg<\/a>[\/caption]\r\n<h2><strong><a id=\"6.3\"><\/a>Part 3: <\/strong><strong>C<\/strong><strong>onnective tissue<\/strong><\/h2>\r\n<h5><strong><a id=\"6.3a\"><\/a>General structure of connective tissue<\/strong><\/h5>\r\n<p style=\"text-align: justify\">As may be obvious from its name, one of the major functions of connective tissue is to connect tissues and organs. Unlike epithelial tissue, which is composed of cells closely packed with little or no extracellular space in between, connective tissue cells are dispersed in a [pb_glossary id=\"2297\"]matrix[\/pb_glossary]. The matrix usually includes a large amount of extracellular material produced by the connective tissue cells that are embedded within it. The matrix plays a major role in the functioning of this tissue. The major component of the matrix is a [pb_glossary id=\"2298\"]ground substance[\/pb_glossary] often crisscrossed by protein fibres. This ground substance is usually a fluid, but it can also be mineralized and solid, as in bones. Connective tissues come in a vast variety of forms, yet they typically have in common three characteristic components: cells, large amounts of amorphous [pb_glossary id=\"2298\"]ground substance[\/pb_glossary], and protein fibres. The amount and structure of each component correlates with the function of the tissue, from the rigid ground substance in bones supporting the body to the inclusion of specialized cells; for example, a [pb_glossary id=\"2227\"]phagocytic[\/pb_glossary] cell that engulfs [pb_glossary id=\"2193\"]pathogens[\/pb_glossary] and also rids tissue of cellular debris.<\/p>\r\n\r\n<h5><strong><a id=\"6.3b\"><\/a>Functions of Connective Tissues<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Connective tissues perform many functions in the body, but most importantly, they support and connect other tissues; from the connective tissue sheath that surrounds muscle cells, to the tendons that attach muscles to bones, and to the skeleton that supports the positions of the body. Protection is another major function of connective tissue, in the form of fibrous capsules and bones that protect delicate organs and, of course, the skeletal system. Specialized cells in connective tissue defend the body from microorganisms that enter the body. Transport of fluid, nutrients, waste, and chemical messengers is ensured by specialized fluid connective tissues, such as blood and [pb_glossary id=\"2138\"]lymph[\/pb_glossary]. [pb_glossary id=\"2300\"]Adipose[\/pb_glossary] cells store surplus energy in the form of fat and contribute to the thermal insulation of the body.<\/p>\r\n\r\n<h5><strong><a id=\"6.3c\"><\/a>Classification of Connective Tissue<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The three broad categories of connective tissue are classified according to the characteristics of their [pb_glossary id=\"2298\"]ground substance[\/pb_glossary] and the types of fibres found within the matrix (Table 1). <strong>[pb_glossary id=\"2301\"]Connective tissue proper[\/pb_glossary]<\/strong> includes <strong>loose connective tissue<\/strong> and <strong>dense connective tissue<\/strong>. Both tissues have a variety of cell types and protein fibres suspended in a [pb_glossary id=\"2302\"]viscous[\/pb_glossary] ground substance. Dense connective tissue is reinforced by bundles of fibres that provide tensile strength, elasticity, and protection. In loose connective tissue, the fibres are loosely organized, leaving large spaces in between. <strong>Supportive connective tissue<\/strong> - <strong>bone<\/strong> and <strong>cartilage<\/strong> - provide structure and strength to the body and protect soft tissues. A few distinct cell types and densely packed fibres in a matrix characterize these tissues. In bone, the matrix is rigid and described as calcified because of the deposited calcium salts. In <strong>fluid connective tissue<\/strong> - <strong>[pb_glossary id=\"2138\"]lymph[\/pb_glossary]<\/strong> and <strong>blood<\/strong> - various specialized cells circulate in a watery fluid containing salts, nutrients, and dissolved proteins.<\/p>\r\n\r\n<table style=\"border-collapse: collapse;width: 100%;height: 311px\" border=\"0\"><caption>Table 1: Connective tissue examples<\/caption>\r\n<tbody>\r\n<tr style=\"height: 14px\">\r\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\">Connective tissue proper<\/th>\r\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\">Supportive connective tissue<\/th>\r\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\">Fluid connective tissue<\/th>\r\n<\/tr>\r\n<tr style=\"height: 114px\">\r\n<td style=\"width: 33.3333%;height: 114px\">Loose connective tissue\r\n<blockquote>\r\n<p style=\"text-align: left\">Areolar<\/p>\r\n<p style=\"text-align: left\">Adipose<\/p>\r\n<p style=\"text-align: left\">Reticular<\/p>\r\n<\/blockquote>\r\n<\/td>\r\n<td style=\"width: 33.3333%;height: 114px\">Cartilage\r\n<blockquote>\r\n<p style=\"text-align: left\">Hyaline<\/p>\r\n<p style=\"text-align: left\">Fibrocartilage<\/p>\r\n<p style=\"text-align: left\">Elastic<\/p>\r\n<\/blockquote>\r\n<\/td>\r\n<td style=\"width: 33.3333%;height: 114px\">Blood<\/td>\r\n<\/tr>\r\n<tr style=\"height: 99px\">\r\n<td style=\"width: 33.3333%;height: 99px\">Dense connective tissue\r\n<blockquote>\r\n<p style=\"text-align: left\">Regular<\/p>\r\n<p style=\"text-align: left\">Irregular<\/p>\r\n<\/blockquote>\r\n<\/td>\r\n<td style=\"width: 33.3333%;height: 99px\">Bones\r\n<blockquote>\r\n<p style=\"text-align: left\">Compact bone<\/p>\r\n<p style=\"text-align: left\">Cancellous bone<\/p>\r\n<\/blockquote>\r\n<\/td>\r\n<td style=\"width: 33.3333%;height: 99px\">Lymph<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n&nbsp;\r\n\r\n<strong>C<\/strong><strong>onnective Tissue Proper<\/strong>\r\n<p style=\"text-align: justify\">[pb_glossary id=\"2303\"]Fibroblasts[\/pb_glossary] are present in all connective tissue proper (Figure 4). Fibroblasts are the most abundant cells in connective tissue proper. [pb_glossary id=\"2304\"]Fibrocytes[\/pb_glossary], [pb_glossary id=\"2305\"]adipocytes[\/pb_glossary], and [pb_glossary id=\"2306\"]mesenchymal[\/pb_glossary] cells are fixed cells, which means they remain within the connective tissue. Other cells move in and out of the connective tissue in response to chemical signals. [pb_glossary id=\"2307\"]Macrophages[\/pb_glossary], [pb_glossary id=\"2308\"]mast cells[\/pb_glossary], [pb_glossary id=\"2309\"]lymphocytes[\/pb_glossary], [pb_glossary id=\"2310\"]plasma cells[\/pb_glossary], and phagocytic cells are found in connective tissue proper but are actually part of the immune system protecting the body.<\/p>\r\n\r\n\r\n[caption id=\"attachment_2881\" align=\"alignnone\" width=\"3900\"]<img class=\"wp-image-2881 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492.png\" alt=\"\" width=\"3900\" height=\"1345\" \/> <strong>Figure 4. Connective Tissue Proper.<\/strong> Fibroblasts produce this fibrous tissue. Connective tissue proper includes the fixed cells fibrocytes, adipocytes, and mesenchymal cells. LM \u00d7 400. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n<p style=\"text-align: justify\"><strong>[pb_glossary id=\"2305\"]Adipocytes[\/pb_glossary]<\/strong> are cells that store lipids as droplets that fill most of the cytoplasm. The <strong>[pb_glossary id=\"2306\"]mesenchymal[\/pb_glossary] cell<\/strong> is a [pb_glossary id=\"2311\"]multipotent[\/pb_glossary] adult [pb_glossary id=\"2240\"]stem cell[\/pb_glossary]. These cells can differentiate into any type of connective tissue cells needed for repair and healing of damaged tissue. The <strong>[pb_glossary id=\"2307\"]macrophage[\/pb_glossary]<\/strong> is a large type of blood cell, which enters the connective tissue matrix from the blood vessels. The macrophage cells are an essential component of the immune system, which is the body\u2019s defense against potential [pb_glossary id=\"2193\"]pathogens[\/pb_glossary] and degraded [pb_glossary id=\"2312\"]host[\/pb_glossary] cells. The <strong>[pb_glossary id=\"2308\"]mast cell[\/pb_glossary]<\/strong> found in [pb_glossary id=\"2301\"]connective tissue proper[\/pb_glossary], when irritated or damaged, release [pb_glossary id=\"2272\"]histamine[\/pb_glossary] which causes [pb_glossary id=\"2313\"]vasodilation[\/pb_glossary] and increased blood flow at a site of injury or infection, along with itching, swelling, and redness you recognize as an allergic response.<\/p>\r\n<p style=\"text-align: justify\">Three main types of fibres are secreted by [pb_glossary id=\"2303\"]fibroblasts[\/pb_glossary]: [pb_glossary id=\"2174\"]collagen[\/pb_glossary] fibres, [pb_glossary id=\"2315\"]elastic fibres[\/pb_glossary], and [pb_glossary id=\"2314\"]reticular[\/pb_glossary] fibres. <strong>[pb_glossary id=\"2174\"]Collagen[\/pb_glossary] fibres<\/strong>, while flexible, have great tensile strength, resist stretching, and give ligaments and tendons their characteristic resilience and strength. These fibres hold connective tissues together, even during the movement of the body. [pb_glossary id=\"2315\"]<strong>Elastic fibre<\/strong><strong>s<\/strong>[\/pb_glossary] after being stretched or compressed will return to its original shape. Elastic fibres are prominent in elastic tissues found in skin and the elastic ligaments of the vertebral column. [pb_glossary id=\"2314\"]<strong>Reticular fibre<\/strong><strong>s<\/strong>[\/pb_glossary] are narrow and are arrayed in a branching network. They are found throughout the body, but are most abundant in the reticular tissue of soft organs, such as liver and spleen, where they anchor and provide structural support to the <strong>[pb_glossary id=\"2316\"]parenchyma[\/pb_glossary]<\/strong> (the functional cells, blood vessels, and nerves of the organ). All of these fibre types are embedded in ground substance, a clear, viscous, colorless matrix made of polysaccharides and proteins, forming the extracellular matrix.<\/p>\r\n<strong>L<\/strong><strong>oose Connective Tissue<\/strong>\r\n<p style=\"text-align: justify\">Loose connective tissue is found between many organs where it acts both to absorb shock and bind tissues together. It allows water, salts, and various nutrients to diffuse through to adjacent or imbedded cells and tissues.<\/p>\r\n<p style=\"text-align: justify\"><strong>Adipose tissue<\/strong> consists mostly of fat storage cells, with little extracellular matrix (Figure 5). A large number of capillaries allow rapid storage and mobilization of lipid molecules. Fat contributes mostly to lipid storage and can serve as insulation from cold temperatures and mechanical injuries.<\/p>\r\n<p style=\"text-align: justify\"><strong>Areolar tissue<\/strong> shows little specialization. It contains all the cell types and fibres previously described and is distributed in a random, web-like fashion. It fills the spaces between muscle fibres, surrounds blood and lymph vessels, and supports organs in the abdominal cavity. Areolar tissue underlies most epithelia and represents the connective tissue component of epithelial membranes, which are described further in a later section.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1587\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image7-5.png\" alt=\"image\" width=\"1587\" height=\"671\" \/> <strong>Figure 5. Adipose Tissue.<\/strong> This is a loose connective tissue that consists of fat cells with little extracellular matrix. It stores fat for energy and provides insulation. LM \u00d7 800. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n<p style=\"text-align: justify\"><strong>Reticular tissue<\/strong> is a mesh-like, supportive framework for soft organs such as lymphatic tissue, the spleen, and the liver (Figure 6). Reticular cells produce the reticular fibres that form the network onto which other cells attach. It derives its name from the Latin reticulus, which means \u201clittle net.\u201d<\/p>\r\n\r\n\r\n[caption id=\"attachment_2801\" align=\"alignnone\" width=\"3900\"]<img class=\"size-full wp-image-2801\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1.png\" alt=\"\" width=\"3900\" height=\"1588\" \/> <strong>Figure 6. Reticular Tissue.<\/strong> This is a loose connective tissue made up of a network of reticular fibres that provides a supportive framework for soft organs. LM \u00d7 1600. (Micrograph provided by the Regents of University of Michigan Medical school2012)[\/caption]\r\n\r\n<strong>Dense Connective Tissue <\/strong>\r\n<p style=\"text-align: justify\">Dense connective tissue (also called fibrous connective tissue) contains more collagen fibres than does loose connective tissue. As a consequence, it displays greater resistance to stretching. There are two major categories of dense connective tissue: <strong>regular <\/strong>and <strong>irregular<\/strong>. Dense regular connective tissue fibres are parallel to each other, enhancing tensile strength and resistance to stretching in the direction of the fibre orientations. Ligaments and tendons are made of dense regular connective tissue, but in ligaments not all fibres are parallel. Dense regular elastic connective tissue contains elastin fibres in addition to collagen fibres, which allows the ligament to return to its original length after stretching. The ligaments in the vocal folds and between the vertebrae in the vertebral column are elastic.<\/p>\r\n<p style=\"text-align: justify\">In dense irregular connective tissue, the direction of fibres is random. This arrangement gives the tissue greater strength in all directions and less strength in one particular direction. In some tissues, fibres crisscross and form a mesh. In other tissues, stretching in several directions is achieved by alternating layers where fibres run in the same orientation in each layer, and it is the layers themselves that are stacked at an angle. The dermis of the skin is an example of dense irregular connective tissue rich in collagen fibres. Dense irregular elastic connective tissue give arterial walls the strength and the ability to regain original shape after stretching (Figure 7).<\/p>\r\n\r\n\r\n[caption id=\"attachment_2802\" align=\"alignnone\" width=\"3900\"]<img class=\"size-full wp-image-2802\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1.png\" alt=\"\" width=\"3900\" height=\"3200\" \/> Figure 7. Dense Connective Tissue. (a) Dense regular connective tissue consists of collagenous fibres packed into parallel bundles. (b) Dense irregular connective tissue consists of collagenous fibres interwoven into a mesh-like network. From top, LM \u00d7 1000, LM \u00d7 200. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n\r\n<strong>Supportive Connective Tissues<\/strong>\r\n<p style=\"text-align: justify\">Two major forms of supportive connective tissue, cartilage and bone, allow the body to maintain its posture and protect internal organs.<\/p>\r\n<strong>Cartilage<\/strong>\r\n<p style=\"text-align: justify\">The distinctive appearance of cartilage is due to polysaccharides, which bind with ground substance proteins to form the extracellular matrix. Embedded within the cartilage matrix are <strong>[pb_glossary id=\"2320\"]chondrocytes[\/pb_glossary]<\/strong>, or cartilage cells, and the space they occupy are called<strong> [pb_glossary id=\"2318\"]lacunae[\/pb_glossary] <\/strong>(singular = lacuna). A layer of dense irregular connective tissue, the [pb_glossary id=\"2319\"]perichondrium[\/pb_glossary], encapsulates the cartilage. Cartilaginous tissue is [pb_glossary id=\"2286\"]avascular[\/pb_glossary], thus all nutrients need to diffuse through the matrix to reach the chondrocytes. This is a factor contributing to the very slow healing of cartilaginous tissues.<\/p>\r\n<p style=\"text-align: justify\">The three main types of cartilage tissue are hyaline cartilage, fibrocartilage, and elastic cartilage (Figure 8). <strong>[pb_glossary id=\"2321\"]Hyaline cartilage[\/pb_glossary]<\/strong>, the most common type of cartilage in the body, contains short and dispersed collagen fibres in the matrix. Both strong and flexible, the hyaline cartilage is found in the rib cage and nose and covers bones where they meet to form moveable joints. It makes up a template of the embryonic skeleton before bone formation. A plate of hyaline cartilage at the ends of bone allows continued growth until adulthood. <strong>[pb_glossary id=\"2322\"]Fibrocartilage[\/pb_glossary]<\/strong> is tough because it has thick bundles of collagen fibres dispersed through its matrix. The knee and jaw joints and the intervertebral discs are examples of fibrocartilage. <strong>[pb_glossary id=\"2323\"]Elastic cartilage[\/pb_glossary]<\/strong> contains [pb_glossary id=\"2315\"]elastic fibres[\/pb_glossary] as well as [pb_glossary id=\"2174\"]collagen[\/pb_glossary]. This tissue gives rigid support as well as elasticity. Tug gently at your ear lobes, and notice that the lobes return to their initial shape. The external ear contains elastic cartilage.<\/p>\r\n\r\n\r\n[caption id=\"attachment_2803\" align=\"alignnone\" width=\"3900\"]<img class=\"size-full wp-image-2803\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8.png\" alt=\"\" width=\"3900\" height=\"4860\" \/> Figure 8. Types of Cartilage. Cartilage is a connective tissue consisting of collagenous fibres embedded in a firm matrix of chondroitin sulfates. (a) Hyaline cartilage provides support with some flexibility. The example is from dog tissue. (b) Fibrocartilage provides some compressibility and can absorb pressure. (c) Elastic cartilage provides firm but elastic support. From top, LM \u00d7 300, LM \u00d7 1200, LM \u00d7 1016. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n\r\n<strong>B<\/strong><strong>one<\/strong>\r\n<p style=\"text-align: justify\">Bone is the hardest connective tissue. It provides protection to internal organs and supports the body. Bone\u2019s rigid extracellular matrix contains mostly collagen fibres embedded in a mineralized ground substance containing [pb_glossary id=\"2324\"]hydroxyapatite[\/pb_glossary], a form of calcium phosphate. Both components of the matrix, organic and inorganic, contribute to the unusual properties of bone. Without collagen, bones would be brittle and shatter easily. Without mineral crystals, bones would flex and provide little support. [pb_glossary id=\"2325\"]Osteocytes[\/pb_glossary], bone cells similar to [pb_glossary id=\"2320\"]chondrocytes[\/pb_glossary], are located within [pb_glossary id=\"2318\"]lacunae[\/pb_glossary]. The [pb_glossary id=\"2279\"]histology[\/pb_glossary] of transverse tissue from long bone shows a typical arrangement of osteocytes in concentric circles around a central canal. Bone is a highly [pb_glossary id=\"2326\"]vascularized[\/pb_glossary] tissue. Unlike cartilage, bone tissue can recover from injuries in a relatively short time.<\/p>\r\n<p style=\"text-align: justify\">[pb_glossary id=\"2327\"]Cancellous bone[\/pb_glossary] (\u201ctrabecular bone\u201d or \u201cspongy bone\u201d) looks like a sponge under the microscope and contains empty spaces between trabeculae, or arches of bone proper. It is lighter than compact bone and found in the interior of some bones and at the end of long bones. Compact bone is solid and has greater structural strength.<\/p>\r\n<strong>Fluid Connective Tissue<\/strong>\r\n<p style=\"text-align: justify\"><strong>Blood<\/strong> and <strong>[pb_glossary id=\"2138\"]lymph[\/pb_glossary]<\/strong> are fluid connective tissues. Cells circulate in a liquid extracellular matrix. The formed elements circulating in blood are all derived from [pb_glossary id=\"2329\"]hematopoietic[\/pb_glossary] [pb_glossary id=\"2240\"]stem cells[\/pb_glossary] located in bone marrow (Figure 9). [pb_glossary id=\"2245\"]Erythrocytes[\/pb_glossary], red blood cells, transport oxygen and some carbon dioxide. [pb_glossary id=\"2246\"]Leukocytes[\/pb_glossary], white blood cells, are responsible for defending against potentially harmful microorganisms or molecules. [pb_glossary id=\"2328\"]Platelets[\/pb_glossary] are cell fragments involved in blood clotting.<\/p>\r\n<p style=\"text-align: justify\">Some white blood cells have the ability to cross the [pb_glossary id=\"2330\"]endothelial[\/pb_glossary] layer that lines blood vessels and enter adjacent tissues. Nutrients, salts, and wastes are dissolved in the liquid matrix and transported through the body.<\/p>\r\n<p style=\"text-align: justify\"><strong>[pb_glossary id=\"2138\"]Lymph[\/pb_glossary]<\/strong> contains a liquid matrix and white blood cells. Lymphatic capillaries are extremely permeable, allowing larger molecules and excess fluid from interstitial spaces to enter the lymphatic vessels. Lymph drains into blood vessels, delivering molecules to the blood that could not otherwise directly enter the bloodstream. In this way, specialized lymphatic capillaries transport absorbed fats away from the intestine and deliver these molecules to the blood.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1437\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image11-3.png\" alt=\"image\" width=\"1437\" height=\"747\" \/> <strong>Figure 9. Blood: A Fluid Connective Tissue.<\/strong> Blood is a fluid connective tissue containing erythrocytes and various types of leukocytes that circulate in a liquid extracellular matrix. LM \u00d7 1600. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n<h2><strong><a id=\"6.4\"><\/a>Part 4: Muscle Tissue<\/strong><\/h2>\r\n<p style=\"text-align: justify\">Muscle tissue is characterized by properties that allow movement. Muscle cells are excitable; they respond to a stimulus. They are contractile, meaning they can shorten and generate a pulling force. When attached between two movable objects, in other words, bones, contractions of the muscles cause the bones to move. Some muscle movement is [pb_glossary id=\"2280\"]voluntary[\/pb_glossary], which means it is under conscious control. For example, a person decides to open a book and read a chapter on anatomy. Other movements are [pb_glossary id=\"2333\"]involuntary[\/pb_glossary], meaning they are not under conscious control, such as the contraction of your pupil in bright light. Muscle tissue is classified into three types according to structure and function: <strong>[pb_glossary id=\"2334\"]skeletal[\/pb_glossary]<\/strong>, <strong>[pb_glossary id=\"2335\"]cardiac[\/pb_glossary]<\/strong>, and <strong>[pb_glossary id=\"2336\"]smooth[\/pb_glossary]<\/strong> (Table 2).<\/p>\r\n\r\n<table style=\"border-collapse: collapse;width: 100%\" border=\"0\"><caption>Table 2: Comparison of structure and properties of muscle tissue types<\/caption>\r\n<tbody>\r\n<tr>\r\n<th style=\"width: 10.9353%\" scope=\"col\">Tissue<\/th>\r\n<th style=\"width: 29.2194%\" scope=\"col\">Histology<\/th>\r\n<th style=\"width: 29.6414%\" scope=\"col\">Function<\/th>\r\n<th style=\"width: 30.2039%\" scope=\"col\">Location<\/th>\r\n<\/tr>\r\n<tr>\r\n<td style=\"width: 10.9353%\">Skeletal<\/td>\r\n<td style=\"width: 29.2194%\">Long cylindrical fibre; striated; many peripherally-located nuclei<\/td>\r\n<td style=\"width: 29.6414%\">Voluntary movement; thermogenesis; organ protection<\/td>\r\n<td style=\"width: 30.2039%\">Attached to bones; found around entrance points to body (e.g. mouth, anus)<\/td>\r\n<\/tr>\r\n<tr>\r\n<td style=\"width: 10.9353%\">Cardiac<\/td>\r\n<td style=\"width: 29.2194%\">Short, branched fibres; striated; single central nucleus<\/td>\r\n<td style=\"width: 29.6414%\">Contracts to pump blood<\/td>\r\n<td style=\"width: 30.2039%\">Heart walls<\/td>\r\n<\/tr>\r\n<tr>\r\n<td style=\"width: 10.9353%\">Smooth<\/td>\r\n<td style=\"width: 29.2194%\">Short, spindle-shaped fibres; no evident striation; single nucleus<\/td>\r\n<td style=\"width: 29.6414%\">Involuntary movement; moves material through digestive tract and ducts; regulates blood flow in arteries<\/td>\r\n<td style=\"width: 30.2039%\">Walls of major organs and passageways<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n&nbsp;\r\n<h5><strong><a id=\"6.4a\"><\/a>Skeletal muscle<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Skeletal muscle is attached to bones and its contraction makes possible locomotion, facial expressions, posture, and other voluntary movements of the body. Forty percent of your body mass is made up of skeletal muscle. Skeletal muscles generate heat as a byproduct of their contraction and thus participate in thermal [pb_glossary id=\"2264\"]homeostasis[\/pb_glossary]. Shivering is an involuntary contraction of skeletal muscles in response to perceived lower than normal body temperature.<\/p>\r\n<p style=\"text-align: justify\">The muscle cells, <strong>muscle fibres<\/strong> or [pb_glossary id=\"2338\"]<strong>myocyte<\/strong><strong>s<\/strong>[\/pb_glossary], and their numbers remain relatively constant throughout life. Skeletal muscle tissue is arranged in bundles surrounded by connective tissue. Under the light microscope, muscle cells appear striated with many nuclei squeezed along the membranes (Figure 10a). The <strong>[pb_glossary id=\"2337\"]striation[\/pb_glossary] <\/strong>is due to the regular alternation of the contractile proteins actin and myosin, along with the structural proteins that couple the contractile proteins to connective tissues. The cells are multinucleated as a result of the fusion of the many myoblasts that fuse to form each long muscle fibre.<\/p>\r\n\r\n<h5><strong><a id=\"6.4b\"><\/a>Cardiac muscle<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Cardiac muscle forms the contractile walls of the heart. The cells of cardiac muscle, known as cardiomyocytes, also appear striated under the microscope. Unlike skeletal muscle fibres, cardiomyocytes are single cells typically with a single centrally located nucleus.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"600\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image13-3.png\" alt=\"image\" width=\"600\" height=\"1043\" \/> <strong>Figure 10. Muscle Tissue.<\/strong> (a) Skeletal muscle cells have prominent striation and nuclei on their periphery. (b) Smooth muscle cells have a single nucleus and no visible striations.(c) Cardiac muscle cells appear striated and have a single nucleus. From top, LM \u00d7 1600, LM \u00d7 1600, LM \u00d7 1600. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n<p style=\"text-align: justify\">A principal characteristic of cardiomyocytes is that they contract on their own intrinsic rhythms without any external stimulation. Cardiomyocyte attach to one another with specialized cell junctions called intercalated discs. Attached cells form long, branching cardiac muscle fibres that are (Figure 10c), essentially, a mechanical and electrochemical [pb_glossary id=\"2339\"]syncytium[\/pb_glossary] allowing the cells to synchronize their actions. The cardiac muscle pumps blood through the body and is under [pb_glossary id=\"2333\"]involuntary[\/pb_glossary] control.<\/p>\r\n<p style=\"text-align: justify\"><strong><a id=\"6.4c\"><\/a>Smooth muscle<\/strong><\/p>\r\n<p style=\"text-align: justify\">Smooth muscle tissue contraction is responsible for [pb_glossary id=\"2333\"]involuntary[\/pb_glossary] movements in the internal organs. It forms the contractile component of the digestive, urinary, and reproductive systems as well as the airways and arteries. Each cell is spindle shaped with a single nucleus and no visible [pb_glossary id=\"2337\"]striations[\/pb_glossary] (Figure 10b).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"216\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image14-2.png\" alt=\"image\" width=\"216\" height=\"222\" \/> Watch <a href=\"https:\/\/youtu.be\/i5tR3csCWYo\">this CrashCourse video<\/a> on tissues to learn more about muscle tissue. Direct link:\u00a0<a href=\"https:\/\/youtu.be\/i5tR3csCWYo\">https:\/\/youtu.be\/i5tR3csCWYo<\/a>[\/caption]\r\n<h2><strong><a id=\"6.5\"><\/a>Part 5: Nervous Tissue<\/strong><\/h2>\r\n<p style=\"text-align: justify\">Nervous tissue is characterized as being excitable and capable of sending and receiving electrochemical signals that provide the body with information. Two main classes of cells make up nervous tissue: the <strong>[pb_glossary id=\"2181\"]neuron[\/pb_glossary]<\/strong> and <strong>[pb_glossary id=\"2340\"]neuroglia[\/pb_glossary] <\/strong>(Figure 11). Neurons propagate information via electrochemical impulses, called [pb_glossary id=\"2341\"]action potentials[\/pb_glossary], which are biochemically linked to the release of chemical signals. Neuroglia play an essential role in supporting neurons and modulating their information propagation.<\/p>\r\n<p style=\"text-align: justify\">Neurons display distinctive morphology, well suited to their role as conducting cells, with three main parts. The cell body includes most of the [pb_glossary id=\"2131\"]cytoplasm[\/pb_glossary], the [pb_glossary id=\"2211\"]organelles[\/pb_glossary], and the [pb_glossary id=\"2221\"]nucleus[\/pb_glossary]. [pb_glossary id=\"2342\"]Dendrites[\/pb_glossary] branch off the cell body and appear as thin extensions. A long \u201ctail,\u201d the [pb_glossary id=\"2345\"]axon[\/pb_glossary], extends from the neuron body and can be wrapped in an insulating layer known as <strong>[pb_glossary id=\"2343\"]myelin[\/pb_glossary]<\/strong>, which is formed by accessory cells. The [pb_glossary id=\"2344\"]synapse[\/pb_glossary] is the gap between nerve cells, or between a nerve cell and its target, for example, a muscle or a gland, across which the impulse is transmitted by chemical compounds known as [pb_glossary id=\"2172\"]neurotransmitters[\/pb_glossary].<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"890\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image15.png\" alt=\"image\" width=\"890\" height=\"578\" \/> <strong>Figure 11. The Neuron.<\/strong> The cell body of a neuron, also called the soma, contains the nucleus and mitochondria. The dendrites transfer the nerve impulse to the soma. The axon carries the action potential away to another excitable cell. LM \u00d7 1600. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n<p style=\"text-align: justify\">The second class of neural cells comprises the [pb_glossary id=\"2340\"]neuroglia[\/pb_glossary] or glial cells (Figure 12), which have been characterized as having a simple support role. The word \u201cglia\u201d comes from the Greek word for glue. Recent research is shedding light on the more complex role of neuroglia in the function of the brain and nervous system.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1373\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image16.png\" alt=\"image\" width=\"1373\" height=\"630\" \/> <strong>Figure 12. Nervous Tissue.<\/strong> Nervous tissue is made up of neurons and neuroglia. The cells of nervous tissue are specialized to transmit and receive impulses. LM \u00d7 872. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n<p style=\"text-align: justify\">The presence of the nervous tissue throughout the body and its organization allow it to receive, integrate and provide information to the entire body. This ensures that appropriate responses can occur among all body systems within an intact organism, both under normal conditions as well as during times of stress.<\/p>\r\n&nbsp;\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\r\n<strong>Part 1.<\/strong> <strong>Tissue: a higher level of organization<\/strong>\r\n\r\n[h5p id=\"121\"]\r\n\r\n<strong>Part 2<\/strong>. <strong>Epithelial tissue<\/strong>\r\n\r\n[h5p id=\"122\"]\r\n\r\n[h5p id=\"130\"]\r\n\r\n<strong>Part 3<\/strong>. <strong>Connective tissue<\/strong>\r\n\r\n[h5p id=\"131\"]\r\n\r\n[h5p id=\"132\"]\r\n\r\n[h5p id=\"133\"]\r\n\r\n[h5p id=\"134\"]\r\n\r\n<strong>Part <\/strong><strong>4<\/strong><strong>.<\/strong> <strong>Muscle tissue<\/strong>\r\n\r\n[h5p id=\"137\"]\r\n\r\n[h5p id=\"135\"]\r\n\r\n<strong>Part <\/strong><strong>5<\/strong>. <strong>Nervous tissue<\/strong>\r\n\r\n[h5p id=\"136\"]\r\n\r\n<\/div>\r\n<\/div>\r\n&nbsp;\r\n\r\n<\/div>","rendered":"<div class=\"unit-6:-tissue-structure-and-functions-\">\n<div class=\"textbox shaded\">\n<p><strong>Unit outline<\/strong><\/p>\n<p><a href=\"#6.1\"><strong>Part 1.<\/strong> Tissue: a higher level of organization<\/a><\/p>\n<ul style=\"margin-top: 1.42857em;margin-bottom: 1.42857em\">\n<li><a href=\"#6.1a\">The four types of tissues<\/a><\/li>\n<\/ul>\n<p><a href=\"#6.2\"><strong>Part 2<\/strong>. Epithelial tissue<\/a><\/p>\n<ul>\n<li><a href=\"#6.2a\">General structure of epithelial tissue<\/a><\/li>\n<li><a href=\"#6.2b\">General functions of epithelial tissue<\/a><\/li>\n<li><a href=\"#6.2c\">Classification of epithelial tissue<\/a><\/li>\n<\/ul>\n<p><a href=\"#6.3\"><strong>Part 3<\/strong>. Connective tissue<\/a><\/p>\n<ul>\n<li><a href=\"#6.3a\">General structure of connective tissue<\/a><\/li>\n<li><a href=\"#6.3b\">Functions of connective tissue<\/a><\/li>\n<li><a href=\"#6.3c\">Classification of connective tissue<\/a><\/li>\n<\/ul>\n<p><a href=\"#6.4\"><strong>Part <\/strong><strong>4<\/strong><strong>.<\/strong> Muscle tissue<\/a><\/p>\n<ul>\n<li><a href=\"#6.4a\">Skeletal muscle<\/a><\/li>\n<li><a href=\"#6.4b\">Cardiac muscle<\/a><\/li>\n<li><a href=\"#6.4c\">Smooth muscle<\/a><\/li>\n<\/ul>\n<p><a href=\"#6.5\"><strong>Part <\/strong><strong>5<\/strong>. Nervous tissue<\/a><\/p>\n<h4><em><a href=\"#P\"><strong>Practice Questions<\/strong><\/a><\/em><\/h4>\n<\/div>\n<p>&nbsp;<\/p>\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><strong>I<\/strong><strong>. <\/strong>Define tissue and describe the importance of tissue level organization to an organism.<\/p>\n<p><strong>II<\/strong><strong>. <\/strong>Describe the structure and function of epithelial, connective, muscle, and nervous tissue.<\/p>\n<p><strong>III<\/strong><strong>.<\/strong> Explain the relationships between structure and function of tissues.<\/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><strong>I<\/strong><strong>. <\/strong>Define tissue and describe the importance of tissue level organization to an organism.<\/p>\n<ol>\n<li>What is a tissue?<\/li>\n<li>What is the main benefit to humans of having tissue level organization?<\/li>\n<\/ol>\n<p><strong>II<\/strong><strong>. <\/strong>Describe the structure and function of epithelial, connective, muscle, and nervous tissue.<\/p>\n<ol>\n<li>Describe the general structure of each of the following:\n<ul>\n<li>Epithelial tissue<\/li>\n<li>Connective tissue<\/li>\n<li>Muscle tissue<\/li>\n<li>Nervous tissue<\/li>\n<\/ul>\n<\/li>\n<li>Describe the general function of each of the following:\n<ul>\n<li>Epithelial tissue<\/li>\n<li>Connective tissue<\/li>\n<li>Muscle tissue<\/li>\n<li>Nervous tissue<\/li>\n<\/ul>\n<\/li>\n<li>Compare and contrast the structure of the three types of connective tissue (proper, supportive connective tissue, and liquid connective tissue).<\/li>\n<li>Compare and contrast the structure of the three types of stratified epithelium (stratified squamous epithelium, stratified cuboidal epithelium, and stratified columnar epithelium).<\/li>\n<\/ol>\n<p><strong>III<\/strong><strong>.<\/strong> Explain the relationships between structure and function of tissues.<\/p>\n<ol>\n<li>Use annotated diagrams to describe the structure and function of each of the seven main types of epithelial tissue (including pseudostratified columnar epithelium).<\/li>\n<li>Compare and contrast the structure and function of:\n<ul>\n<li>Simple squamous epithelium and stratified squamous epithelium<\/li>\n<li>Simple squamous epithelium and simple columnar epithelium<\/li>\n<li>Simple squamous epithelium and simple cuboidal epithelium<\/li>\n<li>Simple cuboidal epithelium and simple columnar epithelium<\/li>\n<li>Simple cuboidal epithelium and stratified cuboidal epithelium<\/li>\n<\/ul>\n<\/li>\n<li>Create a table stating:\n<ul>\n<li>The matrix composition,<\/li>\n<li>The cellular types,<\/li>\n<li>The main function(s), and<\/li>\n<li>Specific examples<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<p style=\"padding-left: 40px\">&#8230;of each of the following types of connective tissue:<\/p>\n<ol>\n<li style=\"list-style-type: none\">\n<ul>\n<li>Fluid connective tissue<\/li>\n<li>Loose connective tissue<\/li>\n<li>Dense connective tissue<\/li>\n<li>Cartilage<\/li>\n<li>Bone<\/li>\n<\/ul>\n<\/li>\n<li>Compare and contrast the three types of muscle tissue by discussing each of the following characteristics:\n<ul>\n<li>The structure of each of the three types of muscle tissue<\/li>\n<li>How each type of muscle tissue is controlled (i.e., whether voluntary control is available or not)<\/li>\n<li>The function(s) of each of the three types of muscle tissue<\/li>\n<\/ul>\n<\/li>\n<li>Name and describe both of the two main cell types in the nervous tissue. In your description, include:\n<ul>\n<li>Their general cellular morphology (i.e., their shape)<\/li>\n<li>Their main function(s)<\/li>\n<\/ul>\n<\/li>\n<li>What is the relationship between the structure and the function of the following tissues?\n<ul>\n<li>Simple squamous epithelium<\/li>\n<li>Stratified squamous epithelium<\/li>\n<li>Fluid connective tissue<\/li>\n<li>Loose connective tissue<\/li>\n<li>Dense connective tissue<\/li>\n<li>Cartilage<\/li>\n<li>Bone<\/li>\n<li>Nervous tissue<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">The body contains at least 200 distinct cell types. These cells contain essentially the same internal structures, yet they vary enormously in shape and function. The different types of cells are not randomly distributed throughout the body; rather they occur in organized layers, a level of organization referred to as tissue.<\/p>\n<h2><strong><a id=\"6.1\"><\/a>Part 1: <\/strong><strong>Tissue: a higher level of organization<\/strong><\/h2>\n<p style=\"text-align: justify\">The term <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2218\">tissue<\/a> <\/strong>is used to describe a group of cells found together in the body. The cells within a tissue share a common embryonic origin. Microscopic observation reveals that the cells in a tissue share morphological features and are arranged in an orderly pattern that achieves the tissue\u2019s functions. From the evolutionary perspective, tissues appear in more complex organisms. For example, multicellular protists, ancient eukaryotes, do not have cells organized into tissues. Having tissue level organization increases the efficiency of the body as different shapes and internal structures are better suited to carry out different functions. Having different tissues for different functions allows for a greater speed of activity and a greater effectiveness in performing the various activities.<\/p>\n<p style=\"text-align: justify\">Although there are many types of cells in the human body, they are organized into four broad categories of tissues: <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2239\">epithelial<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2194\">connective<\/a>, muscle, and nervous. Each of these categories is characterized by specific functions that contribute to the overall health and maintenance of the body. A disruption of the structure is a sign of injury or disease. Such changes can be detected through <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2279\">histology<\/a><\/strong>, the microscopic study of tissue appearance, organization, and function.<\/p>\n<h5><strong><a id=\"6.1a\"><\/a>The Four Types of Tissues<\/strong><\/h5>\n<p style=\"text-align: justify\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2239\">Epithelial tissue<\/a>, also referred to as epithelium, refers to the sheets of cells that cover exterior surfaces of the body, lines internal cavities and passageways, and forms certain glands. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2194\">Connective tissue<\/a>, as its name implies, binds the cells and organs of the body together and functions in the protection, support, and integration of all parts of the body. Muscle tissue is excitable, responding to stimulation and contracting to provide movement, and occurs as three major types: skeletal (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2280\">voluntary<\/a>) muscle, smooth muscle, and cardiac muscle in the heart. Nervous tissue is also excitable, allowing the propagation of electrochemical signals in the form of nerve impulses that communicate between different regions of the body (Figure 1).<\/p>\n<figure style=\"width: 986px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image1-6.png\" alt=\"image\" width=\"986\" height=\"1036\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 1. Four Types of Tissue: Body.<\/strong> The four types of tissues are exemplified in nervous tissue, stratified squamous epithelial tissue, cardiac muscle tissue, and connective tissue in small intestine. Clockwise from nervous tissue, LM \u00d7 872, LM \u00d7 282, LM \u00d7 460, LM \u00d7 800. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p style=\"text-align: justify\">The next level of organization is the organ, where several types of tissues come together to form a working unit. Just as knowing the structure and function of cells helps you in your study of tissues, knowledge of tissues will help you understand how organs function. The epithelial and connective tissues are discussed in detail in this chapter. Muscle and nervous tissues will be discussed only briefly in this section.<\/p>\n<h2><strong><a id=\"6.2\"><\/a>Part 2: <\/strong><strong>Epithelial Tissue<\/strong><\/h2>\n<p style=\"text-align: justify\">Most epithelial tissues are essentially large sheets of cells covering all the surfaces of the body exposed to the outside world, and lining the outside of organs and the body cavities. Epithelium also forms much of the glandular tissue of the body. Skin is not the only area of the body exposed to the outside. Other areas include the airways, the digestive tract, as well as the urinary and reproductive systems, all of which are lined by an epithelium. Hollow organs and body cavities that do not connect to the exterior of the body, which includes, blood vessels and serous membranes, are lined by endothelium (plural = endothelia), which is a type of epithelium.<\/p>\n<h5><strong><a id=\"6.2a\"><\/a>General Structure of Epithelial Tissue<\/strong><\/h5>\n<p style=\"text-align: justify\">All epithelia share some important structural and functional features. This tissue is highly cellular, with little or no extracellular material present between cells. The epithelial cells exhibit polarity with differences in structure and function between the exposed or <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2281\">apical<\/a><\/strong> facing surface of the cell and the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2282\">basal<\/a> <\/strong>surface close to the underlying body structures. Particular structures found in some epithelial cells are an adaptation to specific functions. Certain organelles are segregated to the basal sides, whereas other organelles and extensions, such as cilia, when present, are on the apical surface. The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2283\">basal lamina<\/a><\/strong>, a mixture of glycoproteins and collagen, provides an attachment site for the epithelium, separating it from underlying connective tissue. The basal lamina attaches to a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2284\">reticular lamina<\/a><\/strong>, which is secreted by the underlying connective tissue, forming a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2285\">basement membrane<\/a><\/strong> that helps hold it all together.<\/p>\n<p style=\"text-align: justify\">Epithelial tissues are nearly completely <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2286\">avascular<\/a>. For instance, no blood vessels cross the basement membrane to enter the tissue, and nutrients must come by diffusion or absorption from underlying tissues or the surface. Many epithelial tissues are capable of rapidly replacing damaged and dead cells. Sloughing off of damaged or dead cells is a characteristic of surface epithelium and allows our airways and digestive tracts to rapidly replace damaged cells with new cells.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"6.2b\"><\/a>General Functions of Epithelial Tissue<\/strong><\/h5>\n<p style=\"text-align: justify\">Epithelial tissues provide the body\u2019s first line of protection from physical, chemical, and biological wear and tear. The cells of an epithelium act as gatekeepers of the body controlling permeability and allowing selective transfer of materials across a physical barrier. All substances that enter the body must cross an epithelium. Some epithelia often include structural features that allow the selective transport of molecules and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2093\">ions<\/a> across their cell membranes.<\/p>\n<p style=\"text-align: justify\">Many epithelial cells are capable of secretion and release mucous and specific chemical compounds onto their apical surfaces. The epithelium of the small intestine releases digestive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2173\">enzymes<\/a>, for example. Cells lining the respiratory tract secrete mucous that traps incoming microorganisms and particles. A glandular epithelium contains many secretory cells.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"6.2c\"><\/a>Classification of Epithelial Tissues<\/strong><\/h5>\n<p style=\"text-align: justify\">Epithelial tissues are classified according to the shape of the cells and number of the cell layers formed (Figure 2). Cell shapes can be squamous (flattened and thin), cuboidal (boxy, as wide as it is tall), or columnar (rectangular, taller than it is wide). Similarly, the number of cell layers in the tissue can be one\u2014where every cell rests on the basal lamina\u2014which is a simple epithelium, or more than one, which is a stratified epithelium and only the basal layer of cells rests on the basal lamina. Pseudostratified (pseudo- = \u201cfalse\u201d) describes tissue with a single layer of irregularly shaped cells that give the appearance of more than one layer. Transitional describes a form of specialized stratified epithelium in which the shape of the cells can vary.<\/p>\n<p style=\"text-align: justify\"><strong>Simple Epithelium:<\/strong> The shape of the cells in the single cell layer of simple epithelium reflects the functioning of those cells. The cells in <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2287\">simple squamous epithelium<\/a><\/strong> have the appearance of thin scales. Squamous cell nuclei tend to be flat, horizontal, and elliptical, mirroring the form of the cell. Simple squamous epithelium, because of the thinness of the cell, is present where rapid passage of chemical compounds is observed. The alveoli of lungs where gases diffuse, segments of kidney tubules, and the lining of capillaries are also made of simple squamous epithelial tissue.<\/p>\n<figure style=\"width: 1205px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image2-6.png\" alt=\"image\" width=\"1205\" height=\"969\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 2. Types of Epithelial Tissue.<\/strong> Simple epithelial tissue is organized as a single layer of cells and stratified epithelial tissue is formed by several layers of cells. Pseudostratified epithelial tissue is a single layer of cells that appear to be multiple layers because of the position of their nuclei. Epithelial tissue is further defined by the shape of the apical layer of cells in the tissue.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">In <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2288\">simple cuboidal epithelium<\/a><\/strong>, the nucleus of the box-like cells appears round and is generally located near the center of the cell. These epithelia are active in the secretion and absorptions of molecules. Simple cuboidal epithelia are observed in the lining of the kidney tubules and in the ducts of glands (Figure 3).<\/p>\n<p style=\"text-align: justify\">In <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2289\">simple columnar epithelium<\/a><\/strong>, the nucleus of the tall column-like cells tends to be elongated and located in the basal end of the cells (Figure 3). Like the cuboidal epithelia, this epithelium is active in the absorption and secretion of molecules. Simple columnar epithelium forms the lining of some sections of the digestive system and parts of the female reproductive tract. Ciliated columnar epithelium is composed of simple columnar epithelial cells with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2291\">cilia<\/a> on their <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2281\">apical<\/a> surfaces. These epithelial cells are found in the lining of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2292\">uterine tubes<\/a> and parts of the respiratory system, where the beating of the cilia helps remove particulate matter.<\/p>\n<p style=\"text-align: justify\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2290\">Pseudostratified columnar epithelium<\/a><\/strong> is a type of epithelium that appears to be stratified but instead consists of a single layer of irregularly shaped and differently sized columnar cells. In pseudostratified epithelium, nuclei of neighbouring cells appear at different levels rather than clustered in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2282\">basal<\/a> end (Figure 3). The arrangement gives the appearance of stratification; but in fact, all the cells are in contact with the basal lamina, although some do not reach the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2281\">apical<\/a> surface. Pseudostratified columnar epithelium is found in the respiratory tract, where some of these cells have cilia.<\/p>\n<p style=\"text-align: justify\"><strong>Stratified Epithelium:<\/strong> A stratified epithelium consists of several stacked layers of cells. This epithelium protects against physical and chemical wear and tear. The stratified epithelium is named by the shape of the most apical layer of cells, closest to the free space<strong>. <\/strong><\/p>\n<p style=\"text-align: justify\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2293\">Stratified squamous epithelium<\/a><\/strong> is the most common type of stratified epithelium in the human body. The apical cells are squamous, whereas the basal layer contains either columnar or cuboidal cells. The top layer may be covered with dead cells filled with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2294\">keratin<\/a>. Mammalian skin is an example of this dry, keratinized, stratified squamous epithelium. The lining of the mouth cavity is an example of an nonkeratinized, stratified squamous epithelium. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2295\">Stratified cuboidal epithelium<\/a><\/strong> and<strong> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2296\">stratified columnar epithelium<\/a><\/strong> can also be found in certain glands and ducts, but are uncommon in the human body (Figure 3).<\/p>\n<figure style=\"width: 652px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image3-6.png\" alt=\"image\" width=\"652\" height=\"1045\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 3. Summary of Epithelial Tissue Types.<\/strong> Different types of epithelial tissue serve different functions and are found in different locations in the body.<\/figcaption><\/figure>\n<figure style=\"width: 131px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image4-6.png\" alt=\"image\" width=\"131\" height=\"133\" \/><figcaption class=\"wp-caption-text\">Watch <a href=\"https:\/\/youtu.be\/lUe_RI_m-Vg\">this CrashCourse video<\/a> to learn more about epithelial histology. Direct link:\u00a0<a href=\"https:\/\/youtu.be\/lUe_RI_m-Vg\">https:\/\/youtu.be\/lUe_RI_m-Vg<\/a><\/figcaption><\/figure>\n<h2><strong><a id=\"6.3\"><\/a>Part 3: <\/strong><strong>C<\/strong><strong>onnective tissue<\/strong><\/h2>\n<h5><strong><a id=\"6.3a\"><\/a>General structure of connective tissue<\/strong><\/h5>\n<p style=\"text-align: justify\">As may be obvious from its name, one of the major functions of connective tissue is to connect tissues and organs. Unlike epithelial tissue, which is composed of cells closely packed with little or no extracellular space in between, connective tissue cells are dispersed in a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2297\">matrix<\/a>. The matrix usually includes a large amount of extracellular material produced by the connective tissue cells that are embedded within it. The matrix plays a major role in the functioning of this tissue. The major component of the matrix is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2298\">ground substance<\/a> often crisscrossed by protein fibres. This ground substance is usually a fluid, but it can also be mineralized and solid, as in bones. Connective tissues come in a vast variety of forms, yet they typically have in common three characteristic components: cells, large amounts of amorphous <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2298\">ground substance<\/a>, and protein fibres. The amount and structure of each component correlates with the function of the tissue, from the rigid ground substance in bones supporting the body to the inclusion of specialized cells; for example, a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2227\">phagocytic<\/a> cell that engulfs <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2193\">pathogens<\/a> and also rids tissue of cellular debris.<\/p>\n<h5><strong><a id=\"6.3b\"><\/a>Functions of Connective Tissues<\/strong><\/h5>\n<p style=\"text-align: justify\">Connective tissues perform many functions in the body, but most importantly, they support and connect other tissues; from the connective tissue sheath that surrounds muscle cells, to the tendons that attach muscles to bones, and to the skeleton that supports the positions of the body. Protection is another major function of connective tissue, in the form of fibrous capsules and bones that protect delicate organs and, of course, the skeletal system. Specialized cells in connective tissue defend the body from microorganisms that enter the body. Transport of fluid, nutrients, waste, and chemical messengers is ensured by specialized fluid connective tissues, such as blood and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2138\">lymph<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2300\">Adipose<\/a> cells store surplus energy in the form of fat and contribute to the thermal insulation of the body.<\/p>\n<h5><strong><a id=\"6.3c\"><\/a>Classification of Connective Tissue<\/strong><\/h5>\n<p style=\"text-align: justify\">The three broad categories of connective tissue are classified according to the characteristics of their <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2298\">ground substance<\/a> and the types of fibres found within the matrix (Table 1). <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2301\">Connective tissue proper<\/a><\/strong> includes <strong>loose connective tissue<\/strong> and <strong>dense connective tissue<\/strong>. Both tissues have a variety of cell types and protein fibres suspended in a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2302\">viscous<\/a> ground substance. Dense connective tissue is reinforced by bundles of fibres that provide tensile strength, elasticity, and protection. In loose connective tissue, the fibres are loosely organized, leaving large spaces in between. <strong>Supportive connective tissue<\/strong> &#8211; <strong>bone<\/strong> and <strong>cartilage<\/strong> &#8211; provide structure and strength to the body and protect soft tissues. A few distinct cell types and densely packed fibres in a matrix characterize these tissues. In bone, the matrix is rigid and described as calcified because of the deposited calcium salts. In <strong>fluid connective tissue<\/strong> &#8211; <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2138\">lymph<\/a><\/strong> and <strong>blood<\/strong> &#8211; various specialized cells circulate in a watery fluid containing salts, nutrients, and dissolved proteins.<\/p>\n<table style=\"border-collapse: collapse;width: 100%;height: 311px\">\n<caption>Table 1: Connective tissue examples<\/caption>\n<tbody>\n<tr style=\"height: 14px\">\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\">Connective tissue proper<\/th>\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\">Supportive connective tissue<\/th>\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\">Fluid connective tissue<\/th>\n<\/tr>\n<tr style=\"height: 114px\">\n<td style=\"width: 33.3333%;height: 114px\">Loose connective tissue<\/p>\n<blockquote>\n<p style=\"text-align: left\">Areolar<\/p>\n<p style=\"text-align: left\">Adipose<\/p>\n<p style=\"text-align: left\">Reticular<\/p>\n<\/blockquote>\n<\/td>\n<td style=\"width: 33.3333%;height: 114px\">Cartilage<\/p>\n<blockquote>\n<p style=\"text-align: left\">Hyaline<\/p>\n<p style=\"text-align: left\">Fibrocartilage<\/p>\n<p style=\"text-align: left\">Elastic<\/p>\n<\/blockquote>\n<\/td>\n<td style=\"width: 33.3333%;height: 114px\">Blood<\/td>\n<\/tr>\n<tr style=\"height: 99px\">\n<td style=\"width: 33.3333%;height: 99px\">Dense connective tissue<\/p>\n<blockquote>\n<p style=\"text-align: left\">Regular<\/p>\n<p style=\"text-align: left\">Irregular<\/p>\n<\/blockquote>\n<\/td>\n<td style=\"width: 33.3333%;height: 99px\">Bones<\/p>\n<blockquote>\n<p style=\"text-align: left\">Compact bone<\/p>\n<p style=\"text-align: left\">Cancellous bone<\/p>\n<\/blockquote>\n<\/td>\n<td style=\"width: 33.3333%;height: 99px\">Lymph<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>&nbsp;<\/p>\n<p><strong>C<\/strong><strong>onnective Tissue Proper<\/strong><\/p>\n<p style=\"text-align: justify\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2303\">Fibroblasts<\/a> are present in all connective tissue proper (Figure 4). Fibroblasts are the most abundant cells in connective tissue proper. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2304\">Fibrocytes<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2305\">adipocytes<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2306\">mesenchymal<\/a> cells are fixed cells, which means they remain within the connective tissue. Other cells move in and out of the connective tissue in response to chemical signals. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2307\">Macrophages<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2308\">mast cells<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2309\">lymphocytes<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2310\">plasma cells<\/a>, and phagocytic cells are found in connective tissue proper but are actually part of the immune system protecting the body.<\/p>\n<figure id=\"attachment_2881\" aria-describedby=\"caption-attachment-2881\" style=\"width: 3900px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-2881 size-full\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492.png\" alt=\"\" width=\"3900\" height=\"1345\" srcset=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492.png 3900w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492-300x103.png 300w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492-1024x353.png 1024w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492-768x265.png 768w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492-1536x530.png 1536w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492-2048x706.png 2048w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492-65x22.png 65w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492-225x78.png 225w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-4-2-e1666586389492-350x121.png 350w\" sizes=\"auto, (max-width: 3900px) 100vw, 3900px\" \/><figcaption id=\"caption-attachment-2881\" class=\"wp-caption-text\"><strong>Figure 4. Connective Tissue Proper.<\/strong> Fibroblasts produce this fibrous tissue. Connective tissue proper includes the fixed cells fibrocytes, adipocytes, and mesenchymal cells. LM \u00d7 400. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2305\">Adipocytes<\/a><\/strong> are cells that store lipids as droplets that fill most of the cytoplasm. The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2306\">mesenchymal<\/a> cell<\/strong> is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2311\">multipotent<\/a> adult <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2240\">stem cell<\/a>. These cells can differentiate into any type of connective tissue cells needed for repair and healing of damaged tissue. The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2307\">macrophage<\/a><\/strong> is a large type of blood cell, which enters the connective tissue matrix from the blood vessels. The macrophage cells are an essential component of the immune system, which is the body\u2019s defense against potential <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2193\">pathogens<\/a> and degraded <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2312\">host<\/a> cells. The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2308\">mast cell<\/a><\/strong> found in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2301\">connective tissue proper<\/a>, when irritated or damaged, release <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2272\">histamine<\/a> which causes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2313\">vasodilation<\/a> and increased blood flow at a site of injury or infection, along with itching, swelling, and redness you recognize as an allergic response.<\/p>\n<p style=\"text-align: justify\">Three main types of fibres are secreted by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2303\">fibroblasts<\/a>: <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2174\">collagen<\/a> fibres, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2315\">elastic fibres<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2314\">reticular<\/a> fibres. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2174\">Collagen<\/a> fibres<\/strong>, while flexible, have great tensile strength, resist stretching, and give ligaments and tendons their characteristic resilience and strength. These fibres hold connective tissues together, even during the movement of the body. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2315\"><strong>Elastic fibre<\/strong><strong>s<\/strong><\/a> after being stretched or compressed will return to its original shape. Elastic fibres are prominent in elastic tissues found in skin and the elastic ligaments of the vertebral column. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2314\"><strong>Reticular fibre<\/strong><strong>s<\/strong><\/a> are narrow and are arrayed in a branching network. They are found throughout the body, but are most abundant in the reticular tissue of soft organs, such as liver and spleen, where they anchor and provide structural support to the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2316\">parenchyma<\/a><\/strong> (the functional cells, blood vessels, and nerves of the organ). All of these fibre types are embedded in ground substance, a clear, viscous, colorless matrix made of polysaccharides and proteins, forming the extracellular matrix.<\/p>\n<p><strong>L<\/strong><strong>oose Connective Tissue<\/strong><\/p>\n<p style=\"text-align: justify\">Loose connective tissue is found between many organs where it acts both to absorb shock and bind tissues together. It allows water, salts, and various nutrients to diffuse through to adjacent or imbedded cells and tissues.<\/p>\n<p style=\"text-align: justify\"><strong>Adipose tissue<\/strong> consists mostly of fat storage cells, with little extracellular matrix (Figure 5). A large number of capillaries allow rapid storage and mobilization of lipid molecules. Fat contributes mostly to lipid storage and can serve as insulation from cold temperatures and mechanical injuries.<\/p>\n<p style=\"text-align: justify\"><strong>Areolar tissue<\/strong> shows little specialization. It contains all the cell types and fibres previously described and is distributed in a random, web-like fashion. It fills the spaces between muscle fibres, surrounds blood and lymph vessels, and supports organs in the abdominal cavity. Areolar tissue underlies most epithelia and represents the connective tissue component of epithelial membranes, which are described further in a later section.<\/p>\n<figure style=\"width: 1587px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image7-5.png\" alt=\"image\" width=\"1587\" height=\"671\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 5. Adipose Tissue.<\/strong> This is a loose connective tissue that consists of fat cells with little extracellular matrix. It stores fat for energy and provides insulation. LM \u00d7 800. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Reticular tissue<\/strong> is a mesh-like, supportive framework for soft organs such as lymphatic tissue, the spleen, and the liver (Figure 6). Reticular cells produce the reticular fibres that form the network onto which other cells attach. It derives its name from the Latin reticulus, which means \u201clittle net.\u201d<\/p>\n<figure id=\"attachment_2801\" aria-describedby=\"caption-attachment-2801\" style=\"width: 3900px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-2801\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1.png\" alt=\"\" width=\"3900\" height=\"1588\" srcset=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1.png 3900w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1-300x122.png 300w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1-1024x417.png 1024w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1-768x313.png 768w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1-1536x625.png 1536w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1-2048x834.png 2048w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1-65x26.png 65w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1-225x92.png 225w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-6-1-350x143.png 350w\" sizes=\"auto, (max-width: 3900px) 100vw, 3900px\" \/><figcaption id=\"caption-attachment-2801\" class=\"wp-caption-text\"><strong>Figure 6. Reticular Tissue.<\/strong> This is a loose connective tissue made up of a network of reticular fibres that provides a supportive framework for soft organs. LM \u00d7 1600. (Micrograph provided by the Regents of University of Michigan Medical school2012)<\/figcaption><\/figure>\n<p><strong>Dense Connective Tissue <\/strong><\/p>\n<p style=\"text-align: justify\">Dense connective tissue (also called fibrous connective tissue) contains more collagen fibres than does loose connective tissue. As a consequence, it displays greater resistance to stretching. There are two major categories of dense connective tissue: <strong>regular <\/strong>and <strong>irregular<\/strong>. Dense regular connective tissue fibres are parallel to each other, enhancing tensile strength and resistance to stretching in the direction of the fibre orientations. Ligaments and tendons are made of dense regular connective tissue, but in ligaments not all fibres are parallel. Dense regular elastic connective tissue contains elastin fibres in addition to collagen fibres, which allows the ligament to return to its original length after stretching. The ligaments in the vocal folds and between the vertebrae in the vertebral column are elastic.<\/p>\n<p style=\"text-align: justify\">In dense irregular connective tissue, the direction of fibres is random. This arrangement gives the tissue greater strength in all directions and less strength in one particular direction. In some tissues, fibres crisscross and form a mesh. In other tissues, stretching in several directions is achieved by alternating layers where fibres run in the same orientation in each layer, and it is the layers themselves that are stacked at an angle. The dermis of the skin is an example of dense irregular connective tissue rich in collagen fibres. Dense irregular elastic connective tissue give arterial walls the strength and the ability to regain original shape after stretching (Figure 7).<\/p>\n<figure id=\"attachment_2802\" aria-describedby=\"caption-attachment-2802\" style=\"width: 3900px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-2802\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1.png\" alt=\"\" width=\"3900\" height=\"3200\" srcset=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1.png 3900w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1-300x246.png 300w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1-1024x840.png 1024w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1-768x630.png 768w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1-1536x1260.png 1536w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1-2048x1680.png 2048w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1-65x53.png 65w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1-225x185.png 225w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-7-1-350x287.png 350w\" sizes=\"auto, (max-width: 3900px) 100vw, 3900px\" \/><figcaption id=\"caption-attachment-2802\" class=\"wp-caption-text\">Figure 7. Dense Connective Tissue. (a) Dense regular connective tissue consists of collagenous fibres packed into parallel bundles. (b) Dense irregular connective tissue consists of collagenous fibres interwoven into a mesh-like network. From top, LM \u00d7 1000, LM \u00d7 200. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p><strong>Supportive Connective Tissues<\/strong><\/p>\n<p style=\"text-align: justify\">Two major forms of supportive connective tissue, cartilage and bone, allow the body to maintain its posture and protect internal organs.<\/p>\n<p><strong>Cartilage<\/strong><\/p>\n<p style=\"text-align: justify\">The distinctive appearance of cartilage is due to polysaccharides, which bind with ground substance proteins to form the extracellular matrix. Embedded within the cartilage matrix are <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2320\">chondrocytes<\/a><\/strong>, or cartilage cells, and the space they occupy are called<strong> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2318\">lacunae<\/a> <\/strong>(singular = lacuna). A layer of dense irregular connective tissue, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2319\">perichondrium<\/a>, encapsulates the cartilage. Cartilaginous tissue is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2286\">avascular<\/a>, thus all nutrients need to diffuse through the matrix to reach the chondrocytes. This is a factor contributing to the very slow healing of cartilaginous tissues.<\/p>\n<p style=\"text-align: justify\">The three main types of cartilage tissue are hyaline cartilage, fibrocartilage, and elastic cartilage (Figure 8). <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2321\">Hyaline cartilage<\/a><\/strong>, the most common type of cartilage in the body, contains short and dispersed collagen fibres in the matrix. Both strong and flexible, the hyaline cartilage is found in the rib cage and nose and covers bones where they meet to form moveable joints. It makes up a template of the embryonic skeleton before bone formation. A plate of hyaline cartilage at the ends of bone allows continued growth until adulthood. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2322\">Fibrocartilage<\/a><\/strong> is tough because it has thick bundles of collagen fibres dispersed through its matrix. The knee and jaw joints and the intervertebral discs are examples of fibrocartilage. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2323\">Elastic cartilage<\/a><\/strong> contains <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2315\">elastic fibres<\/a> as well as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2174\">collagen<\/a>. This tissue gives rigid support as well as elasticity. Tug gently at your ear lobes, and notice that the lobes return to their initial shape. The external ear contains elastic cartilage.<\/p>\n<figure id=\"attachment_2803\" aria-describedby=\"caption-attachment-2803\" style=\"width: 3900px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-2803\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8.png\" alt=\"\" width=\"3900\" height=\"4860\" srcset=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8.png 3900w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8-241x300.png 241w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8-822x1024.png 822w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8-768x957.png 768w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8-1233x1536.png 1233w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8-1643x2048.png 1643w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8-65x81.png 65w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8-225x280.png 225w, https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image6-8-350x436.png 350w\" sizes=\"auto, (max-width: 3900px) 100vw, 3900px\" \/><figcaption id=\"caption-attachment-2803\" class=\"wp-caption-text\">Figure 8. Types of Cartilage. Cartilage is a connective tissue consisting of collagenous fibres embedded in a firm matrix of chondroitin sulfates. (a) Hyaline cartilage provides support with some flexibility. The example is from dog tissue. (b) Fibrocartilage provides some compressibility and can absorb pressure. (c) Elastic cartilage provides firm but elastic support. From top, LM \u00d7 300, LM \u00d7 1200, LM \u00d7 1016. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p><strong>B<\/strong><strong>one<\/strong><\/p>\n<p style=\"text-align: justify\">Bone is the hardest connective tissue. It provides protection to internal organs and supports the body. Bone\u2019s rigid extracellular matrix contains mostly collagen fibres embedded in a mineralized ground substance containing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2324\">hydroxyapatite<\/a>, a form of calcium phosphate. Both components of the matrix, organic and inorganic, contribute to the unusual properties of bone. Without collagen, bones would be brittle and shatter easily. Without mineral crystals, bones would flex and provide little support. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2325\">Osteocytes<\/a>, bone cells similar to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2320\">chondrocytes<\/a>, are located within <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2318\">lacunae<\/a>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2279\">histology<\/a> of transverse tissue from long bone shows a typical arrangement of osteocytes in concentric circles around a central canal. Bone is a highly <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2326\">vascularized<\/a> tissue. Unlike cartilage, bone tissue can recover from injuries in a relatively short time.<\/p>\n<p style=\"text-align: justify\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2327\">Cancellous bone<\/a> (\u201ctrabecular bone\u201d or \u201cspongy bone\u201d) looks like a sponge under the microscope and contains empty spaces between trabeculae, or arches of bone proper. It is lighter than compact bone and found in the interior of some bones and at the end of long bones. Compact bone is solid and has greater structural strength.<\/p>\n<p><strong>Fluid Connective Tissue<\/strong><\/p>\n<p style=\"text-align: justify\"><strong>Blood<\/strong> and <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2138\">lymph<\/a><\/strong> are fluid connective tissues. Cells circulate in a liquid extracellular matrix. The formed elements circulating in blood are all derived from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2329\">hematopoietic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2240\">stem cells<\/a> located in bone marrow (Figure 9). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2245\">Erythrocytes<\/a>, red blood cells, transport oxygen and some carbon dioxide. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2246\">Leukocytes<\/a>, white blood cells, are responsible for defending against potentially harmful microorganisms or molecules. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2328\">Platelets<\/a> are cell fragments involved in blood clotting.<\/p>\n<p style=\"text-align: justify\">Some white blood cells have the ability to cross the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2330\">endothelial<\/a> layer that lines blood vessels and enter adjacent tissues. Nutrients, salts, and wastes are dissolved in the liquid matrix and transported through the body.<\/p>\n<p style=\"text-align: justify\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2138\">Lymph<\/a><\/strong> contains a liquid matrix and white blood cells. Lymphatic capillaries are extremely permeable, allowing larger molecules and excess fluid from interstitial spaces to enter the lymphatic vessels. Lymph drains into blood vessels, delivering molecules to the blood that could not otherwise directly enter the bloodstream. In this way, specialized lymphatic capillaries transport absorbed fats away from the intestine and deliver these molecules to the blood.<\/p>\n<figure style=\"width: 1437px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image11-3.png\" alt=\"image\" width=\"1437\" height=\"747\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 9. Blood: A Fluid Connective Tissue.<\/strong> Blood is a fluid connective tissue containing erythrocytes and various types of leukocytes that circulate in a liquid extracellular matrix. LM \u00d7 1600. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<h2><strong><a id=\"6.4\"><\/a>Part 4: Muscle Tissue<\/strong><\/h2>\n<p style=\"text-align: justify\">Muscle tissue is characterized by properties that allow movement. Muscle cells are excitable; they respond to a stimulus. They are contractile, meaning they can shorten and generate a pulling force. When attached between two movable objects, in other words, bones, contractions of the muscles cause the bones to move. Some muscle movement is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2280\">voluntary<\/a>, which means it is under conscious control. For example, a person decides to open a book and read a chapter on anatomy. Other movements are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2333\">involuntary<\/a>, meaning they are not under conscious control, such as the contraction of your pupil in bright light. Muscle tissue is classified into three types according to structure and function: <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2334\">skeletal<\/a><\/strong>, <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2335\">cardiac<\/a><\/strong>, and <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2336\">smooth<\/a><\/strong> (Table 2).<\/p>\n<table style=\"border-collapse: collapse;width: 100%\">\n<caption>Table 2: Comparison of structure and properties of muscle tissue types<\/caption>\n<tbody>\n<tr>\n<th style=\"width: 10.9353%\" scope=\"col\">Tissue<\/th>\n<th style=\"width: 29.2194%\" scope=\"col\">Histology<\/th>\n<th style=\"width: 29.6414%\" scope=\"col\">Function<\/th>\n<th style=\"width: 30.2039%\" scope=\"col\">Location<\/th>\n<\/tr>\n<tr>\n<td style=\"width: 10.9353%\">Skeletal<\/td>\n<td style=\"width: 29.2194%\">Long cylindrical fibre; striated; many peripherally-located nuclei<\/td>\n<td style=\"width: 29.6414%\">Voluntary movement; thermogenesis; organ protection<\/td>\n<td style=\"width: 30.2039%\">Attached to bones; found around entrance points to body (e.g. mouth, anus)<\/td>\n<\/tr>\n<tr>\n<td style=\"width: 10.9353%\">Cardiac<\/td>\n<td style=\"width: 29.2194%\">Short, branched fibres; striated; single central nucleus<\/td>\n<td style=\"width: 29.6414%\">Contracts to pump blood<\/td>\n<td style=\"width: 30.2039%\">Heart walls<\/td>\n<\/tr>\n<tr>\n<td style=\"width: 10.9353%\">Smooth<\/td>\n<td style=\"width: 29.2194%\">Short, spindle-shaped fibres; no evident striation; single nucleus<\/td>\n<td style=\"width: 29.6414%\">Involuntary movement; moves material through digestive tract and ducts; regulates blood flow in arteries<\/td>\n<td style=\"width: 30.2039%\">Walls of major organs and passageways<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>&nbsp;<\/p>\n<h5><strong><a id=\"6.4a\"><\/a>Skeletal muscle<\/strong><\/h5>\n<p style=\"text-align: justify\">Skeletal muscle is attached to bones and its contraction makes possible locomotion, facial expressions, posture, and other voluntary movements of the body. Forty percent of your body mass is made up of skeletal muscle. Skeletal muscles generate heat as a byproduct of their contraction and thus participate in thermal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2264\">homeostasis<\/a>. Shivering is an involuntary contraction of skeletal muscles in response to perceived lower than normal body temperature.<\/p>\n<p style=\"text-align: justify\">The muscle cells, <strong>muscle fibres<\/strong> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2338\"><strong>myocyte<\/strong><strong>s<\/strong><\/a>, and their numbers remain relatively constant throughout life. Skeletal muscle tissue is arranged in bundles surrounded by connective tissue. Under the light microscope, muscle cells appear striated with many nuclei squeezed along the membranes (Figure 10a). The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2337\">striation<\/a> <\/strong>is due to the regular alternation of the contractile proteins actin and myosin, along with the structural proteins that couple the contractile proteins to connective tissues. The cells are multinucleated as a result of the fusion of the many myoblasts that fuse to form each long muscle fibre.<\/p>\n<h5><strong><a id=\"6.4b\"><\/a>Cardiac muscle<\/strong><\/h5>\n<p style=\"text-align: justify\">Cardiac muscle forms the contractile walls of the heart. The cells of cardiac muscle, known as cardiomyocytes, also appear striated under the microscope. Unlike skeletal muscle fibres, cardiomyocytes are single cells typically with a single centrally located nucleus.<\/p>\n<figure style=\"width: 600px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image13-3.png\" alt=\"image\" width=\"600\" height=\"1043\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 10. Muscle Tissue.<\/strong> (a) Skeletal muscle cells have prominent striation and nuclei on their periphery. (b) Smooth muscle cells have a single nucleus and no visible striations.(c) Cardiac muscle cells appear striated and have a single nucleus. From top, LM \u00d7 1600, LM \u00d7 1600, LM \u00d7 1600. (Micrographs provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p style=\"text-align: justify\">A principal characteristic of cardiomyocytes is that they contract on their own intrinsic rhythms without any external stimulation. Cardiomyocyte attach to one another with specialized cell junctions called intercalated discs. Attached cells form long, branching cardiac muscle fibres that are (Figure 10c), essentially, a mechanical and electrochemical <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2339\">syncytium<\/a> allowing the cells to synchronize their actions. The cardiac muscle pumps blood through the body and is under <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2333\">involuntary<\/a> control.<\/p>\n<p style=\"text-align: justify\"><strong><a id=\"6.4c\"><\/a>Smooth muscle<\/strong><\/p>\n<p style=\"text-align: justify\">Smooth muscle tissue contraction is responsible for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2333\">involuntary<\/a> movements in the internal organs. It forms the contractile component of the digestive, urinary, and reproductive systems as well as the airways and arteries. Each cell is spindle shaped with a single nucleus and no visible <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2337\">striations<\/a> (Figure 10b).<\/p>\n<figure style=\"width: 216px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image14-2.png\" alt=\"image\" width=\"216\" height=\"222\" \/><figcaption class=\"wp-caption-text\">Watch <a href=\"https:\/\/youtu.be\/i5tR3csCWYo\">this CrashCourse video<\/a> on tissues to learn more about muscle tissue. Direct link:\u00a0<a href=\"https:\/\/youtu.be\/i5tR3csCWYo\">https:\/\/youtu.be\/i5tR3csCWYo<\/a><\/figcaption><\/figure>\n<h2><strong><a id=\"6.5\"><\/a>Part 5: Nervous Tissue<\/strong><\/h2>\n<p style=\"text-align: justify\">Nervous tissue is characterized as being excitable and capable of sending and receiving electrochemical signals that provide the body with information. Two main classes of cells make up nervous tissue: the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2181\">neuron<\/a><\/strong> and <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2340\">neuroglia<\/a> <\/strong>(Figure 11). Neurons propagate information via electrochemical impulses, called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2341\">action potentials<\/a>, which are biochemically linked to the release of chemical signals. Neuroglia play an essential role in supporting neurons and modulating their information propagation.<\/p>\n<p style=\"text-align: justify\">Neurons display distinctive morphology, well suited to their role as conducting cells, with three main parts. The cell body includes most of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2131\">cytoplasm<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2211\">organelles<\/a>, and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2221\">nucleus<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2342\">Dendrites<\/a> branch off the cell body and appear as thin extensions. A long \u201ctail,\u201d the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2345\">axon<\/a>, extends from the neuron body and can be wrapped in an insulating layer known as <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2343\">myelin<\/a><\/strong>, which is formed by accessory cells. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2344\">synapse<\/a> is the gap between nerve cells, or between a nerve cell and its target, for example, a muscle or a gland, across which the impulse is transmitted by chemical compounds known as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2172\">neurotransmitters<\/a>.<\/p>\n<figure style=\"width: 890px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image15.png\" alt=\"image\" width=\"890\" height=\"578\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 11. The Neuron.<\/strong> The cell body of a neuron, also called the soma, contains the nucleus and mitochondria. The dendrites transfer the nerve impulse to the soma. The axon carries the action potential away to another excitable cell. LM \u00d7 1600. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p style=\"text-align: justify\">The second class of neural cells comprises the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1322_2340\">neuroglia<\/a> or glial cells (Figure 12), which have been characterized as having a simple support role. The word \u201cglia\u201d comes from the Greek word for glue. Recent research is shedding light on the more complex role of neuroglia in the function of the brain and nervous system.<\/p>\n<figure style=\"width: 1373px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/07\/image16.png\" alt=\"image\" width=\"1373\" height=\"630\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 12. Nervous Tissue.<\/strong> Nervous tissue is made up of neurons and neuroglia. The cells of nervous tissue are specialized to transmit and receive impulses. LM \u00d7 872. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<p style=\"text-align: justify\">The presence of the nervous tissue throughout the body and its organization allow it to receive, integrate and provide information to the entire body. This ensures that appropriate responses can occur among all body systems within an intact organism, both under normal conditions as well as during times of stress.<\/p>\n<p>&nbsp;<\/p>\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><strong>Part 1.<\/strong> <strong>Tissue: a higher level of organization<\/strong><\/p>\n<div id=\"h5p-121\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-121\" class=\"h5p-iframe\" data-content-id=\"121\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-1\"><\/iframe><\/div>\n<\/div>\n<p><strong>Part 2<\/strong>. <strong>Epithelial tissue<\/strong><\/p>\n<div id=\"h5p-122\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-122\" class=\"h5p-iframe\" data-content-id=\"122\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-2\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-130\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-130\" class=\"h5p-iframe\" data-content-id=\"130\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-3\"><\/iframe><\/div>\n<\/div>\n<p><strong>Part 3<\/strong>. <strong>Connective tissue<\/strong><\/p>\n<div id=\"h5p-131\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-131\" class=\"h5p-iframe\" data-content-id=\"131\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-4\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-132\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-132\" class=\"h5p-iframe\" data-content-id=\"132\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-5\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-133\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-133\" class=\"h5p-iframe\" data-content-id=\"133\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-6\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-134\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-134\" class=\"h5p-iframe\" data-content-id=\"134\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-7\"><\/iframe><\/div>\n<\/div>\n<p><strong>Part <\/strong><strong>4<\/strong><strong>.<\/strong> <strong>Muscle tissue<\/strong><\/p>\n<div id=\"h5p-137\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-137\" class=\"h5p-iframe\" data-content-id=\"137\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-7a\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-135\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-135\" class=\"h5p-iframe\" data-content-id=\"135\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-8\"><\/iframe><\/div>\n<\/div>\n<p><strong>Part <\/strong><strong>5<\/strong>. <strong>Nervous tissue<\/strong><\/p>\n<div id=\"h5p-136\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-136\" class=\"h5p-iframe\" data-content-id=\"136\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6-9\"><\/iframe><\/div>\n<\/div>\n<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<\/div>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_1322_2218\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2218\"><div tabindex=\"-1\"><p>Group of many similar cells (though sometimes composed of a few related types) that work together to perform a specific function.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2239\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2239\"><div tabindex=\"-1\"><p>Type of tissue that serves primarily as a covering or lining of body parts, protecting the body; it also functions in absorption, transport, and 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_1322_2194\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2194\"><div tabindex=\"-1\"><p>Type of tissue that serves to hold in place, connect, and integrate the body\u2019s organs and systems.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2279\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2279\"><div tabindex=\"-1\"><p>Microscopic study of tissue architecture, organization, and function.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2280\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2280\"><div tabindex=\"-1\"><p>(In physiology) under conscious control of the brain.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2281\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2281\"><div tabindex=\"-1\"><p>That part of a cell or tissue which, in general, faces an open space.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2282\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2282\"><div tabindex=\"-1\"><p>That part of a tissue close to underlying body structures.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2283\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2283\"><div tabindex=\"-1\"><p>Thin extracellular layer that lies underneath epithelial cells and separates them from other tissues.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2284\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2284\"><div tabindex=\"-1\"><p>Matrix containing collagen and elastin secreted by connective tissue; a component of the basement membrane.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2285\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2285\"><div tabindex=\"-1\"><p>In epithelial tissue, a thin layer of fibrous material that anchors the epithelial tissue to the underlying connective tissue; made up of the basal lamina and reticular lamina.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2286\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2286\"><div tabindex=\"-1\"><p>Lacking blood vessels.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2093\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2093\"><div tabindex=\"-1\"><p>Atom with an overall positive or negative charge. Many function as electrolytes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2173\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2173\"><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_1322_2287\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2287\"><div tabindex=\"-1\"><p>Tissue that consists of a single layer of flat scale-like cells; promotes diffusion and filtration across surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2288\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2288\"><div tabindex=\"-1\"><p>Tissue that consists of a single layer of cube-shaped cells; promotes secretion and absorption in ducts and tubules.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2289\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2289\"><div tabindex=\"-1\"><p>Tissue that consists of a single layer of column-like cells; promotes secretion and absorption in tissues and organs.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2291\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2291\"><div tabindex=\"-1\"><p>Small appendage on certain cells formed by microtubules and modified for movement of materials across the cellular surface (singular = cilium).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2292\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2292\"><div tabindex=\"-1\"><p>(Also, fallopian tube or oviduct) duct that facilitates transport of an ovulated oocyte to the uterus.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2290\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2290\"><div tabindex=\"-1\"><p>Tissue that consists of a single layer of irregularly shaped and sized cells that give the appearance of multiple layers; found in ducts of certain glands and the upper respiratory tract.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2293\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2293\"><div tabindex=\"-1\"><p>Tissue that consists of multiple layers of cells with the most apical being flat scale-like cells; protects surfaces from abrasion.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2294\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2294\"><div tabindex=\"-1\"><p>Type of structural protein that gives skin, hair, and nails its hard, water-resistant properties.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2295\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2295\"><div tabindex=\"-1\"><p>Tissue that consists of two or more layers of cube-shaped cells, found in some ducts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2296\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2296\"><div tabindex=\"-1\"><p>Tissue that consists of two or more layers of column-like cells, contains glands and is found in some ducts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2297\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2297\"><div tabindex=\"-1\"><p>(In connective tissue) extracellular material which is produced by the cells embedded in it, containing ground substance and fibres.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2298\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2298\"><div tabindex=\"-1\"><p>Fluid or semi-fluid portion of the matrix.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2227\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2227\"><div tabindex=\"-1\"><p>Cell process (a form of endocytosis) in which a cell engulfs and ingests another large particle or 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_1322_2193\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2193\"><div tabindex=\"-1\"><p>An infectious agent that causes disease, typically a bacterium, virus, fungus, or microscopic parasite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2138\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2138\"><div tabindex=\"-1\"><p>Fluid contained within the lymphatic system, consisting of interstitial fluid, leukocytes (white blood cells), proteins (including antibodies) and fats.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2300\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2300\"><div tabindex=\"-1\"><p>Specialized areolar tissue rich in stored fat.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2301\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2301\"><div tabindex=\"-1\"><p>Connective tissue containing a viscous matrix, fibers, and 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_1322_2302\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2302\"><div tabindex=\"-1\"><p>Thick consistency between solid and liquid.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2303\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2303\"><div tabindex=\"-1\"><p>Most abundant cell type in connective tissue, secretes protein fibers and matrix into the extracellular space.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2304\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2304\"><div tabindex=\"-1\"><p>Mature, less active form of a fibroblast.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2305\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2305\"><div tabindex=\"-1\"><p>Lipid storage 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_1322_2306\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2306\"><div tabindex=\"-1\"><p>Embryonic tissue from which connective tissue cells derive.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2307\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2307\"><div tabindex=\"-1\"><p>Ameboid (irregular outline with peripheral projections) phagocyte found in several tissues throughout 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_1322_2308\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2308\"><div tabindex=\"-1\"><p>Cell found in the skin and the lining of body cells that contains cytoplasmic granules with vasoactive mediators such as histamine.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2309\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2309\"><div tabindex=\"-1\"><p>White blood cell characterized by a large nucleus and small rim of cytoplasm.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2310\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2310\"><div tabindex=\"-1\"><p>Differentiated B cell that is actively secreting antibody.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2311\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2311\"><div tabindex=\"-1\"><p>Describes the condition of being able to differentiate into different types of cells within a given cell lineage or small number of lineages, such as a red blood cell or white blood 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_1322_2240\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2240\"><div tabindex=\"-1\"><p>Cell that is oligo-, multi-, or pleuripotent that has the ability to produce additional stem cells rather than becoming further specialized.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2312\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2312\"><div tabindex=\"-1\"><p>(in immunology) referring to the organism in, or on, which a pathogen lives.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2272\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2272\"><div tabindex=\"-1\"><p>Vasoactive (active on blood vessels) mediator in granules of mast cells and is the primary cause of allergies and anaphylactic shock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2313\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2313\"><div tabindex=\"-1\"><p>Opening up, or increasing interior (lumen) diameter of a blood vessel.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2174\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2174\"><div tabindex=\"-1\"><p>The most abundant of three protein fibres found in the extracellular matrix of connective tissues.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2315\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2315\"><div tabindex=\"-1\"><p>Fibrous protein within connective tissue that contains a high percentage of the protein elastin that allows the fibers to stretch and return to original size.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2314\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2314\"><div tabindex=\"-1\"><p>Fine fibrous protein, made of collagen subunits, which cross-link to form supporting \u201cnets\u201d within connective tissue.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2316\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2316\"><div tabindex=\"-1\"><p>Functional cells of a gland or organ, in contrast with the supportive or connective tissue of a gland or organ.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2320\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2320\"><div tabindex=\"-1\"><p>cartilage 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_1322_2318\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2318\"><div tabindex=\"-1\"><p>(Plural= lacunae) small spaces in bone or cartilage tissue that cells occupy.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2319\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2319\"><div tabindex=\"-1\"><p>Layer of dense irregular connective tissue surrounding cartilage.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2321\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2321\"><div tabindex=\"-1\"><p>Most common type of cartilage, smooth and made of short collagen fibers embedded in a chondroitin sulfate ground substance.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2322\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2322\"><div tabindex=\"-1\"><p>Tough form of cartilage, made of thick bundles of collagen fibers embedded in chondroitin sulfate ground substance.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2323\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2323\"><div tabindex=\"-1\"><p>Type of cartilage, with elastin as the major protein, characterized by rigid support as well as elasticity.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2324\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2324\"><div tabindex=\"-1\"><p>A form of calcium phosphate mineral found in bones (also hydroxylapatite)<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2325\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2325\"><div tabindex=\"-1\"><p>Primary cell in mature bone; responsible for maintaining the matrix.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2326\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2326\"><div tabindex=\"-1\"><p>Relating to circulation of 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_1322_2327\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2327\"><div tabindex=\"-1\"><p>(Also, cancellous bone) trabeculated osseous tissue that supports shifts in weight distribution.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2329\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2329\"><div tabindex=\"-1\"><p>(Also, hematopoiesis) production of the formed elements of 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_1322_2245\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2245\"><div tabindex=\"-1\"><p>Red blood 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_1322_2246\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2246\"><div tabindex=\"-1\"><p>White blood 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_1322_2328\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2328\"><div tabindex=\"-1\"><p>(Also, thrombocytes) one of the formed elements of blood that consists of cell fragments broken off from megakaryocytes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2330\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2330\"><div tabindex=\"-1\"><p>Layer of smooth, simple squamous epithelium that lines the endocardium and blood vessels.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2333\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2333\"><div tabindex=\"-1\"><p>(In physiology) though under nervous control (usually from the brain), control is not conscious.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2334\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2334\"><div tabindex=\"-1\"><p>Usually attached to bone, under voluntary control, each cell is a fiber that is multinucleated and striated.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2335\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2335\"><div tabindex=\"-1\"><p>Heart muscle, under involuntary control, composed of striated cells that attach to form fibres, each cell contains a single nucleus, contracts autonomously.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2336\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2336\"><div tabindex=\"-1\"><p>Under involuntary control, moves internal organs, cells contain a single nucleus, are spindle-shaped, and do not appear striated; each cell is a fibre<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2264\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2264\"><div tabindex=\"-1\"><p>Steady state of body systems 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_1322_2338\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2338\"><div tabindex=\"-1\"><p>Muscle cell (also muscle fibre).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2337\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2337\"><div tabindex=\"-1\"><p>Alignment of parallel actin and myosin filaments which form a banded pattern.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2339\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2339\"><div tabindex=\"-1\"><p>A multinucleate cell formed by the fusion of multiple cells or the division of 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_1322_2181\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2181\"><div tabindex=\"-1\"><p>Excitable neural cell that transfer nerve impulses.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2340\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2340\"><div tabindex=\"-1\"><p>Supportive neural 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_1322_2341\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2341\"><div tabindex=\"-1\"><p>Change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibres.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2131\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2131\"><div tabindex=\"-1\"><p>Internal material between the cell membrane and nucleus of a cell, mainly consisting of a water-based fluid called cytosol, within which are all the other organelles and cellular solute and suspended materials.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2211\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2211\"><div tabindex=\"-1\"><p>Any of several different types of membrane-enclosed specialized structures in the cell that perform specific functions for the 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_1322_2221\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2221\"><div tabindex=\"-1\"><p>Cell\u2019s central organelle; contains the cell\u2019s DNA.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2342\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2342\"><div tabindex=\"-1\"><p>One of many branchlike processes that extends from the neuron cell body and functions as a contact for incoming signals (synapses) from other neurons or sensory 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_1322_2345\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2345\"><div tabindex=\"-1\"><p>Single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a 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_1322_2343\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2343\"><div tabindex=\"-1\"><p>Lipid-rich insulating substance surrounding the axons of many neurons, allowing for faster transmission of electrical signals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1322_2344\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2344\"><div tabindex=\"-1\"><p>Narrow junction across which a chemical signal passes from neuron to the next, initiating a new electrical signal 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_1322_2172\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1322_2172\"><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><\/div>","protected":false},"author":10,"menu_order":6,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1322","chapter","type-chapter","status-publish","hentry"],"part":19,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters\/1322","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/users\/10"}],"version-history":[{"count":25,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters\/1322\/revisions"}],"predecessor-version":[{"id":3241,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters\/1322\/revisions\/3241"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/parts\/19"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters\/1322\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/media?parent=1322"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapter-type?post=1322"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/contributor?post=1322"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/license?post=1322"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}