{"id":478,"date":"2023-12-04T10:25:24","date_gmt":"2023-12-04T15:25:24","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/chapter\/the-endocrine-pancreas\/"},"modified":"2023-12-04T10:51:18","modified_gmt":"2023-12-04T15:51:18","slug":"the-endocrine-pancreas","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/chapter\/the-endocrine-pancreas\/","title":{"raw":"Anatomy of the Pancreas and Glucose Homeostasis","rendered":"Anatomy of the Pancreas and Glucose Homeostasis"},"content":{"raw":"\n<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\n<p class=\"textbox__title\">Learning Objectives<\/p>\n\n<\/header>\n<div class=\"textbox__content\">\n\nBy the end of this section, you will be able to:\n<ul>\n \t<li>Describe the location and structure of the pancreas, and the morphology and function of the pancreatic islets<\/li>\n \t<li>Compare and contrast the functions of insulin and glucagon<\/li>\n<\/ul>\n<\/div>\n<\/div>\nThe <span data-type=\"term\">[pb_glossary id=\"1081\"]pancreas[\/pb_glossary]<\/span> is a long, slender organ, most of which is located posterior to the bottom half of the stomach (<a class=\"autogenerated-content\" href=\"#fig-ch18_09_01\">Figure 7.1<\/a>). Although it is primarily an exocrine gland, secreting a variety of digestive enzymes, the pancreas has an endocrine function. Its <span data-type=\"term\">[pb_glossary id=\"1082\"]pancreatic islets[\/pb_glossary]<\/span>\u2014clusters of cells formerly known as the islets of Langerhans\u2014secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide (PP).\n\n[caption id=\"\" align=\"aligncenter\" width=\"500\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-content\/uploads\/sites\/2131\/2023\/12\/1820_The_Pancreas.jpg\" alt=\"This diagram shows the anatomy of the pancreas. The left, larger side of the pancreas is seated within the curve of the duodenum of the small intestine. The smaller, rightmost tip of the pancreas is located near the spleen. The splenic artery is seen travelling to the spleen, however, it has several branches connecting to the pancreas. An interior view of the pancreas shows that the pancreatic duct is a large tube running through the center of the pancreas. It branches throughout its length in to several horseshoe- shaped pockets of acinar cells. These cells secrete digestive enzymes, which travel down the bile duct and into the small intestine. There are also small pancreatic islets scattered throughout the pancreas. The pancreatic islets secrete the pancreatic hormones insulin and glucagon into the splenic artery. An inset micrograph shows that the pancreatic islets are small discs of tissue consisting of a thin, outer ring called the exocrine acinus, a thicker, inner ring of beta cells and a central circle of alpha cells.\" width=\"500\" height=\"551\" data-media-type=\"image\/jpg\"> <strong>Figure 7.1<\/strong>&nbsp;<em>The Pancreas, upper duodenum, and spleen The pancreatic exocrine function involves the acinar cells secreting digestive enzymes that are transported into the duodenum by the pancreatic duct. Its endocrine function involves the secretion of the hormones insulin and glucagon within the pancreatic islets. These two hormones regulate the rate of glucose metabolism in the body. The micrograph reveals pancreatic islets. LM \u00d7 760. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012).&nbsp; View the <a href=\"http:\/\/openstax.org\/l\/pancreaticislet\">University of Michigan Webscope <\/a>to explore the tissue sample in greater detail.<\/em>[\/caption]\n<h3>Cells and Secretions of the Pancreatic Islets<\/h3>\nThe pancreatic islets each contain four varieties of cells:\n<ul>\n \t<li>[pb_glossary id=\"1076\"]alpha cell[\/pb_glossary]&nbsp; produces the hormone glucagon and makes up approximately 20 percent of each islet. Glucagon plays an important role in blood glucose regulation; low blood glucose levels stimulate its release.<\/li>\n \t<li>[pb_glossary id=\"1077\"]beta cell[\/pb_glossary]&nbsp;produces the hormone insulin and makes up approximately 75 percent of each islet. Elevated blood glucose levels stimulate the release of insulin.<\/li>\n \t<li>[pb_glossary id=\"1078\"]delta cell[\/pb_glossary]&nbsp;accounts for four percent of the islet cells and secretes the peptide hormone somatostatin. Recall that somatostatin is also released by the hypothalamus (as GHIH), and the stomach and intestines also secrete it. An inhibiting hormone, pancreatic somatostatin inhibits the release of both glucagon and insulin.<\/li>\n \t<li>[pb_glossary id=\"1083\"]PP cell[\/pb_glossary]&nbsp;accounts for about one percent of islet cells and secretes the pancreatic polypeptide hormone. It is thought to play a role in appetite, as well as in the regulation of pancreatic exocrine and endocrine secretions. Pancreatic polypeptide released following a meal may reduce further food consumption; however, it is also released in response to fasting.<\/li>\n<\/ul>\n<h3>Regulation of Blood Glucose Levels by Insulin and Glucagon<\/h3>\nGlucose is required for ATP production in the process of cellular respiration and is the preferred fuel for all body cells. The body derives glucose from the breakdown of the carbohydrate-containing foods and drinks we consume. Glucose not immediately taken up by cells for fuel can be stored by the liver and muscles as glycogen, or converted to triglycerides and stored in the adipose tissue. Hormones regulate both the storage and the utilization of glucose as required. Receptors located in the pancreas sense blood glucose levels, and subsequently the pancreatic cells secrete glucagon or insulin to maintain normal levels.\n\nFor example, it is expected that high blood glucose levels (hyperglycemia) will occur after a meal.&nbsp; To control this influx of blood glucose, specific endocrine cells in the pancreas first detect excess glucose in the bloodstream. These pancreatic beta cells then respond to the increased level of blood glucose by releasing the peptide hormone <span class=\"search-highlight first text last focus\" data-timestamp=\"1661660615590\" data-highlight-id=\"94340a9e-fc55-4f04-a595-3c901e067ea2\" data-highlighted=\"true\">insulin<\/span> into the bloodstream. Once bound to cell surface insulin receptors, i<span class=\"search-highlight first text last\" data-timestamp=\"1661660615600\" data-highlight-id=\"f9e91e28-0c6c-42ee-87a8-33c440fed5b9\" data-highlighted=\"true\">nsulin stimulates cells of the body to increase the number of glucose transporters present in their plasma membranes.&nbsp; This allows cells to uptake glucose.&nbsp; Insulin also<\/span> signals skeletal muscle fibers, fat cells (adipocytes), and liver cells to take up the excess glucose, removing it from the bloodstream.&nbsp; As glucose concentration in the bloodstream drops, this decrease in concentration is detected by pancreatic beta cells and stimulates a negative feedback loop, and <span class=\"search-highlight first text last\" data-timestamp=\"1661660615611\" data-highlight-id=\"f3801779-6064-4844-b046-f1de1e2f4702\" data-highlighted=\"true\">insulin<\/span> production and secretion stops. This prevents blood sugar levels from continuing to drop below the normal range.\n<h4>Glucagon<\/h4>\nReceptors in the pancreas can sense the decline in blood glucose levels, such as during periods of fasting or during prolonged exercise (<a class=\"autogenerated-content\" href=\"#fig-ch18_09_02\">Figure 7.2<\/a>). In response, the alpha cells of the pancreas secrete the hormone <span data-type=\"term\">[pb_glossary id=\"1079\"]glucagon[\/pb_glossary]<\/span>, which has several effects:\n<ul>\n \t<li>It stimulates the liver to convert its stores of glycogen back into glucose. This response is known as glycogenolysis. The glucose is then released into the circulation for use by body cells.<\/li>\n \t<li>It stimulates the liver to take up amino acids from the blood and convert them into glucose. This response is known as gluconeogenesis.<\/li>\n \t<li>It stimulates lipolysis, the breakdown of stored triglycerides into free fatty acids and glycerol. Some of the free glycerol released into the bloodstream travels to the liver, which converts it into glucose. This is also a form of gluconeogenesis.<\/li>\n<\/ul>\nTaken together, these actions increase blood glucose levels. The activity of glucagon is regulated through a negative feedback mechanism; rising blood glucose levels inhibit further glucagon production and secretion.\n\n[caption id=\"\" align=\"aligncenter\" width=\"550\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-content\/uploads\/sites\/2131\/2023\/12\/1822_The_Homostatic_Regulation_of_Blood_Glucose_Levels.jpg\" alt=\"This diagram shows the homeostatic regulation of blood glucose levels. Blood glucose concentration is tightly maintained between 70 milligrams per deciliter and 110 milligrams per deciliter. If blood glucose concentration rises above this range (hyperglycemia), insulin is released from the pancreas. Insulin triggers body cells to take up glucose from the blood and utilize it in cellular respiration. Insulin also inhibits glycogenolysis, in that glucose is removed from the blood and stored as glycogen in the liver. Insulin also inhibits gluconeogenesis, in that amino acids and free glycerol are not converted to glucose in the ER. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood. All of these actions cause blood glucose concentration to decrease. When blood glucose concentration is low (hypoglycemia), alpha cells of the pancreas release glucagon. Glucagon inhibits body cells from taking up glucose from the blood and utilizing it in cellular respiration. Glucagon also stimulates glycogenolysis, in that glycogen in the liver is broken down into glucose and released into the blood. Glucagon also stimulates glucogenogenesis, in that amino acids and free glycerol are converted to glucose in the ER and released into the blood. All of these actions cause blood glucose concentrations to increase.\" width=\"550\" height=\"1478\" data-media-type=\"image\/jpg\"> <strong>Figure 7.2<\/strong> <em>Homeostatic Regulation of Blood Glucose Levels Blood glucose concentration is tightly maintained between 70 mg\/dL and 110 mg\/dL. If blood glucose concentration rises above this range, insulin is released, which stimulates body cells to remove glucose from the blood. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood.<\/em>[\/caption]\n<h4>Insulin<\/h4>\nThe primary function of <span data-type=\"term\">[pb_glossary id=\"1080\"]insulin[\/pb_glossary]<\/span>&nbsp;is to facilitate the uptake of glucose into body cells. Red blood cells, as well as cells of the brain, liver, kidneys, and the lining of the small intestine, do not have insulin receptors on their cell membranes and do not require insulin for glucose uptake. Although all other body cells do require insulin if they are to take glucose from the bloodstream, skeletal muscle cells and adipose cells are the primary targets of insulin.\n\nThe presence of food in the intestine triggers the release of gastrointestinal tract hormones such as glucose-dependent insulinotropic peptide (previously known as gastric inhibitory peptide). This is in turn the initial trigger for insulin production and secretion by the beta cells of the pancreas. Once nutrient absorption occurs, the resulting surge in blood glucose levels further stimulates insulin secretion.\n\nPrecisely how insulin facilitates glucose uptake is not entirely clear. However, insulin appears to activate a tyrosine kinase receptor, triggering the phosphorylation of many substrates within the cell. These multiple biochemical reactions converge to support the movement of intracellular vesicles containing facilitative glucose transporters to the cell membrane. In the absence of insulin, these transport proteins are normally recycled slowly between the cell membrane and cell interior. Insulin triggers the rapid movement of a pool of glucose transporter vesicles to the cell membrane, where they fuse and expose the glucose transporters to the extracellular fluid. The transporters then move glucose by facilitated diffusion into the cell interior.\n\nVisit this <a href=\"http:\/\/openstax.org\/l\/pancreas1\">link<\/a> to view an animation describing the location and function of the pancreas.\n\nInsulin also reduces blood glucose levels by stimulating glycolysis, the metabolism of glucose for generation of ATP. Moreover, it stimulates the liver to convert excess glucose into glycogen for storage, and it inhibits enzymes involved in glycogenolysis and gluconeogenesis. Finally, insulin promotes triglyceride and protein synthesis. The secretion of insulin is regulated through a negative feedback mechanism. As blood glucose levels decrease, further insulin release is inhibited. The pancreatic hormones are summarized in <a class=\"autogenerated-content\" href=\"#tbl-ch18_07\">(Figure 7.3)<\/a>.\n<table id=\"tbl-ch18_07\" class=\"top-titled\" summary=\"\">\n<thead>\n<tr>\n<th colspan=\"3\">Hormones of the Pancreas<\/th>\n<\/tr>\n<tr>\n<th>Associated hormones<\/th>\n<th>Chemical class<\/th>\n<th>Effect<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Insulin (beta cells)<\/td>\n<td>Protein<\/td>\n<td>Reduces blood glucose levels<\/td>\n<\/tr>\n<tr>\n<td>Glucagon (alpha cells)<\/td>\n<td>Protein<\/td>\n<td>Increases blood glucose levels<\/td>\n<\/tr>\n<tr>\n<td>Somatostatin (delta cells)<\/td>\n<td>Protein<\/td>\n<td>Inhibits insulin and glucagon release<\/td>\n<\/tr>\n<tr>\n<td>Pancreatic polypeptide (PP cells)<\/td>\n<td>Protein<\/td>\n<td>Role in appetite<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div id=\"fs-id1888088\" class=\"anatomy disorders\" data-type=\"note\" data-has-label=\"true\" data-label=\"\"><strong>Figure 7.3<\/strong> <em>Hormones of the Pancreas<\/em><\/div>\n<div id=\"fs-id1653453\" class=\"summary\" data-depth=\"1\">\n<p id=\"fs-id1884720\"><\/p>\n\n<\/div>\n<div id=\"fs-id2019147\" class=\"interactive-exercise\" data-depth=\"1\">\n<div id=\"fs-id1235247\" data-type=\"exercise\">\n<div data-type=\"solution\" data-label=\"\"><\/div>\n<div id=\"fs-id1947180\" data-type=\"solution\" data-label=\"\"><\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1648796\" class=\"free-response\" data-depth=\"1\">\n<div id=\"fs-id1200690\" data-type=\"exercise\">\n<div id=\"fs-id1388730\" data-type=\"solution\" data-label=\"\">\n\n&nbsp;\n<h1>Adaptation<\/h1>\nThis chapter is adapted from the following text:\n\nEndocrine Pancreas <strong>in <\/strong><a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/17-9-the-endocrine-pancreas\">Anatomy and Physiology<\/a>&nbsp;by&nbsp;OSCRiceUniversity&nbsp;is licensed under a&nbsp;<a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">Creative Commons Attribution 4.0 International License<\/a>\n\n<\/div>\n<\/div>\n<\/div>\n","rendered":"<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\">Learning Objectives<\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Describe the location and structure of the pancreas, and the morphology and function of the pancreatic islets<\/li>\n<li>Compare and contrast the functions of insulin and glucagon<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<p>The <span data-type=\"term\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_478_1081\">pancreas<\/a><\/span> is a long, slender organ, most of which is located posterior to the bottom half of the stomach (<a class=\"autogenerated-content\" href=\"#fig-ch18_09_01\">Figure 7.1<\/a>). Although it is primarily an exocrine gland, secreting a variety of digestive enzymes, the pancreas has an endocrine function. Its <span data-type=\"term\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_478_1082\">pancreatic islets<\/a><\/span>\u2014clusters of cells formerly known as the islets of Langerhans\u2014secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide (PP).<\/p>\n<figure style=\"width: 500px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-content\/uploads\/sites\/2131\/2023\/12\/1820_The_Pancreas.jpg\" alt=\"This diagram shows the anatomy of the pancreas. The left, larger side of the pancreas is seated within the curve of the duodenum of the small intestine. The smaller, rightmost tip of the pancreas is located near the spleen. The splenic artery is seen travelling to the spleen, however, it has several branches connecting to the pancreas. An interior view of the pancreas shows that the pancreatic duct is a large tube running through the center of the pancreas. It branches throughout its length in to several horseshoe- shaped pockets of acinar cells. These cells secrete digestive enzymes, which travel down the bile duct and into the small intestine. There are also small pancreatic islets scattered throughout the pancreas. The pancreatic islets secrete the pancreatic hormones insulin and glucagon into the splenic artery. An inset micrograph shows that the pancreatic islets are small discs of tissue consisting of a thin, outer ring called the exocrine acinus, a thicker, inner ring of beta cells and a central circle of alpha cells.\" width=\"500\" height=\"551\" data-media-type=\"image\/jpg\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 7.1<\/strong>&nbsp;<em>The Pancreas, upper duodenum, and spleen The pancreatic exocrine function involves the acinar cells secreting digestive enzymes that are transported into the duodenum by the pancreatic duct. Its endocrine function involves the secretion of the hormones insulin and glucagon within the pancreatic islets. These two hormones regulate the rate of glucose metabolism in the body. The micrograph reveals pancreatic islets. LM \u00d7 760. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012).&nbsp; View the <a href=\"http:\/\/openstax.org\/l\/pancreaticislet\">University of Michigan Webscope <\/a>to explore the tissue sample in greater detail.<\/em><\/figcaption><\/figure>\n<h3>Cells and Secretions of the Pancreatic Islets<\/h3>\n<p>The pancreatic islets each contain four varieties of cells:<\/p>\n<ul>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_478_1076\">alpha cell<\/a>&nbsp; produces the hormone glucagon and makes up approximately 20 percent of each islet. Glucagon plays an important role in blood glucose regulation; low blood glucose levels stimulate its release.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_478_1077\">beta cell<\/a>&nbsp;produces the hormone insulin and makes up approximately 75 percent of each islet. Elevated blood glucose levels stimulate the release of insulin.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_478_1078\">delta cell<\/a>&nbsp;accounts for four percent of the islet cells and secretes the peptide hormone somatostatin. Recall that somatostatin is also released by the hypothalamus (as GHIH), and the stomach and intestines also secrete it. An inhibiting hormone, pancreatic somatostatin inhibits the release of both glucagon and insulin.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_478_1083\">PP cell<\/a>&nbsp;accounts for about one percent of islet cells and secretes the pancreatic polypeptide hormone. It is thought to play a role in appetite, as well as in the regulation of pancreatic exocrine and endocrine secretions. Pancreatic polypeptide released following a meal may reduce further food consumption; however, it is also released in response to fasting.<\/li>\n<\/ul>\n<h3>Regulation of Blood Glucose Levels by Insulin and Glucagon<\/h3>\n<p>Glucose is required for ATP production in the process of cellular respiration and is the preferred fuel for all body cells. The body derives glucose from the breakdown of the carbohydrate-containing foods and drinks we consume. Glucose not immediately taken up by cells for fuel can be stored by the liver and muscles as glycogen, or converted to triglycerides and stored in the adipose tissue. Hormones regulate both the storage and the utilization of glucose as required. Receptors located in the pancreas sense blood glucose levels, and subsequently the pancreatic cells secrete glucagon or insulin to maintain normal levels.<\/p>\n<p>For example, it is expected that high blood glucose levels (hyperglycemia) will occur after a meal.&nbsp; To control this influx of blood glucose, specific endocrine cells in the pancreas first detect excess glucose in the bloodstream. These pancreatic beta cells then respond to the increased level of blood glucose by releasing the peptide hormone <span class=\"search-highlight first text last focus\" data-timestamp=\"1661660615590\" data-highlight-id=\"94340a9e-fc55-4f04-a595-3c901e067ea2\" data-highlighted=\"true\">insulin<\/span> into the bloodstream. Once bound to cell surface insulin receptors, i<span class=\"search-highlight first text last\" data-timestamp=\"1661660615600\" data-highlight-id=\"f9e91e28-0c6c-42ee-87a8-33c440fed5b9\" data-highlighted=\"true\">nsulin stimulates cells of the body to increase the number of glucose transporters present in their plasma membranes.&nbsp; This allows cells to uptake glucose.&nbsp; Insulin also<\/span> signals skeletal muscle fibers, fat cells (adipocytes), and liver cells to take up the excess glucose, removing it from the bloodstream.&nbsp; As glucose concentration in the bloodstream drops, this decrease in concentration is detected by pancreatic beta cells and stimulates a negative feedback loop, and <span class=\"search-highlight first text last\" data-timestamp=\"1661660615611\" data-highlight-id=\"f3801779-6064-4844-b046-f1de1e2f4702\" data-highlighted=\"true\">insulin<\/span> production and secretion stops. This prevents blood sugar levels from continuing to drop below the normal range.<\/p>\n<h4>Glucagon<\/h4>\n<p>Receptors in the pancreas can sense the decline in blood glucose levels, such as during periods of fasting or during prolonged exercise (<a class=\"autogenerated-content\" href=\"#fig-ch18_09_02\">Figure 7.2<\/a>). In response, the alpha cells of the pancreas secrete the hormone <span data-type=\"term\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_478_1079\">glucagon<\/a><\/span>, which has several effects:<\/p>\n<ul>\n<li>It stimulates the liver to convert its stores of glycogen back into glucose. This response is known as glycogenolysis. The glucose is then released into the circulation for use by body cells.<\/li>\n<li>It stimulates the liver to take up amino acids from the blood and convert them into glucose. This response is known as gluconeogenesis.<\/li>\n<li>It stimulates lipolysis, the breakdown of stored triglycerides into free fatty acids and glycerol. Some of the free glycerol released into the bloodstream travels to the liver, which converts it into glucose. This is also a form of gluconeogenesis.<\/li>\n<\/ul>\n<p>Taken together, these actions increase blood glucose levels. The activity of glucagon is regulated through a negative feedback mechanism; rising blood glucose levels inhibit further glucagon production and secretion.<\/p>\n<figure style=\"width: 550px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-content\/uploads\/sites\/2131\/2023\/12\/1822_The_Homostatic_Regulation_of_Blood_Glucose_Levels.jpg\" alt=\"This diagram shows the homeostatic regulation of blood glucose levels. Blood glucose concentration is tightly maintained between 70 milligrams per deciliter and 110 milligrams per deciliter. If blood glucose concentration rises above this range (hyperglycemia), insulin is released from the pancreas. Insulin triggers body cells to take up glucose from the blood and utilize it in cellular respiration. Insulin also inhibits glycogenolysis, in that glucose is removed from the blood and stored as glycogen in the liver. Insulin also inhibits gluconeogenesis, in that amino acids and free glycerol are not converted to glucose in the ER. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood. All of these actions cause blood glucose concentration to decrease. When blood glucose concentration is low (hypoglycemia), alpha cells of the pancreas release glucagon. Glucagon inhibits body cells from taking up glucose from the blood and utilizing it in cellular respiration. Glucagon also stimulates glycogenolysis, in that glycogen in the liver is broken down into glucose and released into the blood. Glucagon also stimulates glucogenogenesis, in that amino acids and free glycerol are converted to glucose in the ER and released into the blood. All of these actions cause blood glucose concentrations to increase.\" width=\"550\" height=\"1478\" data-media-type=\"image\/jpg\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 7.2<\/strong> <em>Homeostatic Regulation of Blood Glucose Levels Blood glucose concentration is tightly maintained between 70 mg\/dL and 110 mg\/dL. If blood glucose concentration rises above this range, insulin is released, which stimulates body cells to remove glucose from the blood. If blood glucose concentration drops below this range, glucagon is released, which stimulates body cells to release glucose into the blood.<\/em><\/figcaption><\/figure>\n<h4>Insulin<\/h4>\n<p>The primary function of <span data-type=\"term\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_478_1080\">insulin<\/a><\/span>&nbsp;is to facilitate the uptake of glucose into body cells. Red blood cells, as well as cells of the brain, liver, kidneys, and the lining of the small intestine, do not have insulin receptors on their cell membranes and do not require insulin for glucose uptake. Although all other body cells do require insulin if they are to take glucose from the bloodstream, skeletal muscle cells and adipose cells are the primary targets of insulin.<\/p>\n<p>The presence of food in the intestine triggers the release of gastrointestinal tract hormones such as glucose-dependent insulinotropic peptide (previously known as gastric inhibitory peptide). This is in turn the initial trigger for insulin production and secretion by the beta cells of the pancreas. Once nutrient absorption occurs, the resulting surge in blood glucose levels further stimulates insulin secretion.<\/p>\n<p>Precisely how insulin facilitates glucose uptake is not entirely clear. However, insulin appears to activate a tyrosine kinase receptor, triggering the phosphorylation of many substrates within the cell. These multiple biochemical reactions converge to support the movement of intracellular vesicles containing facilitative glucose transporters to the cell membrane. In the absence of insulin, these transport proteins are normally recycled slowly between the cell membrane and cell interior. Insulin triggers the rapid movement of a pool of glucose transporter vesicles to the cell membrane, where they fuse and expose the glucose transporters to the extracellular fluid. The transporters then move glucose by facilitated diffusion into the cell interior.<\/p>\n<p>Visit this <a href=\"http:\/\/openstax.org\/l\/pancreas1\">link<\/a> to view an animation describing the location and function of the pancreas.<\/p>\n<p>Insulin also reduces blood glucose levels by stimulating glycolysis, the metabolism of glucose for generation of ATP. Moreover, it stimulates the liver to convert excess glucose into glycogen for storage, and it inhibits enzymes involved in glycogenolysis and gluconeogenesis. Finally, insulin promotes triglyceride and protein synthesis. The secretion of insulin is regulated through a negative feedback mechanism. As blood glucose levels decrease, further insulin release is inhibited. The pancreatic hormones are summarized in <a class=\"autogenerated-content\" href=\"#tbl-ch18_07\">(Figure 7.3)<\/a>.<\/p>\n<table id=\"tbl-ch18_07\" class=\"top-titled\" summary=\"\">\n<thead>\n<tr>\n<th colspan=\"3\">Hormones of the Pancreas<\/th>\n<\/tr>\n<tr>\n<th>Associated hormones<\/th>\n<th>Chemical class<\/th>\n<th>Effect<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Insulin (beta cells)<\/td>\n<td>Protein<\/td>\n<td>Reduces blood glucose levels<\/td>\n<\/tr>\n<tr>\n<td>Glucagon (alpha cells)<\/td>\n<td>Protein<\/td>\n<td>Increases blood glucose levels<\/td>\n<\/tr>\n<tr>\n<td>Somatostatin (delta cells)<\/td>\n<td>Protein<\/td>\n<td>Inhibits insulin and glucagon release<\/td>\n<\/tr>\n<tr>\n<td>Pancreatic polypeptide (PP cells)<\/td>\n<td>Protein<\/td>\n<td>Role in appetite<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<div id=\"fs-id1888088\" class=\"anatomy disorders\" data-type=\"note\" data-has-label=\"true\" data-label=\"\"><strong>Figure 7.3<\/strong> <em>Hormones of the Pancreas<\/em><\/div>\n<div id=\"fs-id1653453\" class=\"summary\" data-depth=\"1\">\n<p id=\"fs-id1884720\">\n<\/div>\n<div id=\"fs-id2019147\" class=\"interactive-exercise\" data-depth=\"1\">\n<div id=\"fs-id1235247\" data-type=\"exercise\">\n<div data-type=\"solution\" data-label=\"\"><\/div>\n<div id=\"fs-id1947180\" data-type=\"solution\" data-label=\"\"><\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1648796\" class=\"free-response\" data-depth=\"1\">\n<div id=\"fs-id1200690\" data-type=\"exercise\">\n<div id=\"fs-id1388730\" data-type=\"solution\" data-label=\"\">\n<p>&nbsp;<\/p>\n<h1>Adaptation<\/h1>\n<p>This chapter is adapted from the following text:<\/p>\n<p>Endocrine Pancreas <strong>in <\/strong><a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/17-9-the-endocrine-pancreas\">Anatomy and Physiology<\/a>&nbsp;by&nbsp;OSCRiceUniversity&nbsp;is licensed under a&nbsp;<a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">Creative Commons Attribution 4.0 International License<\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_478_1081\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_478_1081\"><div tabindex=\"-1\"><p>organ with both exocrine and endocrine functions located posterior to the stomach that is important for digestion and the regulation of blood glucose<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_478_1082\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_478_1082\"><div tabindex=\"-1\"><p>specialized clusters of pancreatic cells that have endocrine functions; also called islets of Langerhans<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_478_1076\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_478_1076\"><div tabindex=\"-1\"><p>pancreatic islet cell type that produces the hormone glucagon<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_478_1077\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_478_1077\"><div tabindex=\"-1\"><p>pancreatic islet cell type that produces the hormone insulin<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_478_1078\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_478_1078\"><div tabindex=\"-1\"><p>minor cell type in the pancreas that secretes the hormone somatostatin<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_478_1083\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_478_1083\"><div tabindex=\"-1\"><p>minor cell type in the pancreas that secretes the hormone pancreatic polypeptide<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_478_1079\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_478_1079\"><div tabindex=\"-1\"><p>pancreatic hormone that stimulates the catabolism of glycogen to glucose, thereby increasing blood glucose levels<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_478_1080\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_478_1080\"><div tabindex=\"-1\"><p>pancreatic hormone that enhances the cellular uptake and utilization of glucose, thereby decreasing blood glucose levels<\/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":103,"menu_order":4,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["j-gordon-betts-xthrkeeivi","kelly-a-young-oshuupwjvs","james-a-wise-d1yrtemlzk","eddie-johnson-kzduhmaxdi","brandon-poe-pdu6v9qtf4","dean-h-kruse-iwhh7sghex","oksana-korol-1jgnlzwovs","jody-e-johnson-gmyqec8nhu","mark-womble-9aswiv74hr","peter-desaix-kvcjvl9h4v"],"pb_section_license":"cc-by"},"chapter-type":[],"contributor":[166],"license":[53],"class_list":["post-478","chapter","type-chapter","status-publish","hentry","contributor-peter-desaix-kvcjvl9h4v","license-cc-by"],"part":472,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/pressbooks\/v2\/chapters\/478","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/wp\/v2\/users\/103"}],"version-history":[{"count":1,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/pressbooks\/v2\/chapters\/478\/revisions"}],"predecessor-version":[{"id":1301,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/pressbooks\/v2\/chapters\/478\/revisions\/1301"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/pressbooks\/v2\/parts\/472"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/pressbooks\/v2\/chapters\/478\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/wp\/v2\/media?parent=478"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/pressbooks\/v2\/chapter-type?post=478"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/wp\/v2\/contributor?post=478"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol2200\/wp-json\/wp\/v2\/license?post=478"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}