17.9 The Endocrine Pancreas
3 min read•june 18, 2024
The plays a crucial role in regulating blood glucose levels through its endocrine function. , scattered throughout the organ, contain specialized cells that secrete hormones like and to maintain .
and work in tandem to keep blood sugar balanced. When glucose levels rise, release insulin to promote glucose uptake and storage. Conversely, when glucose levels drop, secrete glucagon to increase blood sugar.
Pancreatic Islets and Glucose Regulation
Structure of pancreatic islets
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- Pancreatic islets () are clusters of endocrine cells scattered throughout the pancreas constitute 1-2% of the pancreatic mass
- Contain several cell types that secrete different hormones (insulin, glucagon, , )
- Alpha cells (α cells) comprise 15-20% of the islet cells secrete glucagon stimulates and in the liver increasing blood glucose levels
- Beta cells (β cells) most abundant cell type in the islets (65-80%) stimulated by high blood glucose levels to release insulin promotes glucose uptake by cells and storage of glucose as glycogen decreasing blood glucose levels
- Beta cells also produce , which helps regulate glucose metabolism by slowing gastric emptying and promoting satiety
- (δ cells) comprise 3-10% of the islet cells secrete somatostatin inhibits the secretion of insulin and glucagon
- (F cells) comprise 1% of the islet cells secrete pancreatic polypeptide regulates pancreatic exocrine and endocrine secretion
Insulin and glucagon in glucose regulation
- Insulin lowers blood glucose levels by:
- Stimulating glucose uptake by skeletal muscle and adipose tissue via
- Promoting (conversion of glucose to glycogen) in the liver and muscle
- Inhibiting and glycogenolysis in the liver
- Enhancing and protein synthesis
- Glucagon increases blood glucose levels by:
- Stimulating glycogenolysis in the liver releasing glucose into the bloodstream
- Promoting gluconeogenesis in the liver producing glucose from non-carbohydrate sources (amino acids, lipids)
- Enhancing in adipose tissue providing energy substrates for gluconeogenesis
- Insulin and glucagon work together to maintain blood glucose homeostasis
- determines the net effect on blood glucose levels
- High insulin-to-glucagon ratio favors glucose storage and utilization lowering blood glucose
- Low insulin-to-glucagon ratio favors glucose production and release raising blood glucose
- determines the net effect on blood glucose levels
Effects of pancreatic hormones
- Somatostatin:
- Inhibits the secretion of insulin and glucagon from pancreatic islets
- Suppresses the release of growth hormone (GH) and thyroid-stimulating hormone (TSH) from the anterior pituitary
- Reduces the secretion of gastrin, cholecystokinin (CCK), and secretin from the gastrointestinal tract decreasing gastrointestinal motility and nutrient absorption
- Pancreatic polypeptide (PP):
- Inhibits pancreatic exocrine secretion of digestive enzymes
- Reduces gallbladder contraction and bile secretion
- Slows gastric emptying and intestinal motility
- Suppresses appetite by acting on the hypothalamus
- Modulates the secretion of other pancreatic hormones (insulin, glucagon) but the exact effects are not well understood
Incretin hormones and glucose regulation
- and are incretin hormones that enhance in response to glucose
- These hormones are released by intestinal cells in response to food intake and play a crucial role in glucose homeostasis
- Incretins also inhibit glucagon secretion, slow gastric emptying, and promote satiety
Diabetes mellitus
- is an autoimmune disorder characterized by destruction of pancreatic beta cells, leading to insulin deficiency
- is characterized by insulin resistance and/or decreased insulin production, often associated with obesity and lifestyle factors
Key Terms to Review (39)
Alpha cell: Alpha cells are a type of cell found in the pancreas that produce and secrete glucagon, a hormone that increases blood glucose levels by stimulating the liver to convert stored glycogen into glucose. They play a crucial role in maintaining glucose homeostasis, especially during fasting states.
Alpha Cells: Alpha cells are a type of endocrine cell found in the pancreas that produce the hormone glucagon. Glucagon is a crucial hormone that helps regulate blood glucose levels by stimulating the liver to release stored glucose into the bloodstream.
Amylin: Amylin is a hormone co-secreted by the pancreatic beta cells along with insulin. It plays a key role in regulating glucose and energy homeostasis by complementing the actions of insulin in the body.
Beta cell: Beta cells are specialized cells located in the islets of Langerhans in the pancreas that produce and release insulin, a hormone essential for regulating blood sugar levels. These cells respond to rising blood glucose by secreting insulin, which facilitates the uptake of glucose by body tissues.
Beta Cells: Beta cells are a type of endocrine cell found in the pancreatic islets that are responsible for producing and secreting the hormone insulin. They play a crucial role in regulating blood glucose levels and maintaining glucose homeostasis in the body.
C-peptide: C-peptide is a byproduct of insulin production in the pancreas. It is released into the bloodstream along with insulin and is often used as a marker for insulin secretion and pancreatic beta cell function.
Delta cell: Delta cells are a type of cell found in the pancreas that produce and secrete the hormone somatostatin, which plays an important role in regulating the digestive system by inhibiting the release of certain other hormones. They are part of the endocrine functions of the pancreatic islets (islets of Langerhans), contributing to the body's overall hormonal balance.
Delta Cells: Delta cells are a type of endocrine cell found in the pancreatic islets that secrete the hormone somatostatin. They play a crucial role in regulating insulin and glucagon secretion, as well as overall glucose homeostasis in the body.
Diabetes mellitus: Diabetes Mellitus is a chronic condition characterized by high levels of sugar (glucose) in the blood due to the body's inability to produce or properly use insulin, a hormone produced by the pancreas that regulates blood sugar. This dysfunction can lead to serious health complications if not managed properly.
Glucagon: Glucagon is a hormone produced by the alpha cells in the pancreas that raises blood glucose levels by promoting the conversion of stored glycogen to glucose in the liver. It plays a critical role in glucose homeostasis, especially during periods of fasting or low blood sugar.
Glucagon: Glucagon is a hormone produced by the alpha cells of the pancreatic islets. As a key regulator of glucose metabolism, glucagon plays a crucial role in the endocrine system, carbohydrate metabolism, and overall metabolic states of the body.
Glucagon-Like Peptide-1 (GLP-1): Glucagon-like peptide-1 (GLP-1) is an incretin hormone produced by intestinal L cells that plays a crucial role in regulating glucose homeostasis and insulin secretion. It is a key component of the endocrine pancreas and its functions are closely tied to the maintenance of normal blood sugar levels.
Gluconeogenesis: Gluconeogenesis is a metabolic process by which the body produces glucose from non-carbohydrate sources, such as amino acids, lactate, and glycerol. This pathway is crucial for maintaining blood glucose levels during periods of fasting or intense exercise.
Gluconeogenesis: Gluconeogenesis is the metabolic process by which the body synthesizes glucose from non-carbohydrate precursors, such as amino acids, lactate, and glycerol. This process is crucial for maintaining blood glucose levels, especially during periods of fasting or prolonged exercise when carbohydrate stores are depleted.
Glucose Homeostasis: Glucose homeostasis refers to the physiological process of maintaining a stable and optimal level of glucose in the body. It is a crucial function of the endocrine pancreas, which is responsible for regulating blood glucose levels through the secretion of hormones like insulin and glucagon.
Glucose Transporters: Glucose transporters are a family of membrane-bound proteins that facilitate the facilitated diffusion of glucose across cell membranes. They play a crucial role in regulating glucose homeostasis and energy metabolism within the body, particularly in the context of the endocrine pancreas.
Glucose-Dependent Insulinotropic Polypeptide (GIP): Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone produced by enteroendocrine K cells in the small intestine. It is responsible for stimulating the release of insulin from pancreatic beta cells in response to the ingestion of glucose and other nutrients, thereby playing a crucial role in glucose homeostasis and the regulation of blood sugar levels.
GLUT4: GLUT4 is a glucose transporter protein that plays a crucial role in the regulation of glucose homeostasis and energy metabolism. It is primarily expressed in insulin-responsive tissues, such as skeletal muscle and adipose tissue, and is responsible for facilitating the uptake of glucose into these cells in response to insulin stimulation.
Glycogenesis: Glycogenesis is the biochemical process of converting glucose into glycogen for storage in the liver and muscle cells. This process plays a crucial role in maintaining blood glucose levels and energy reserves, connecting to various functions of human life, the regulation of hormones from the pancreas, metabolic states of the body, and the overall impact of nutrition and diet on health.
Glycogenolysis: Glycogenolysis is the metabolic process by which glycogen, the storage form of glucose in the body, is broken down into glucose. This process occurs primarily in the liver and skeletal muscles, providing a readily available source of glucose for energy production when needed by the body.
Hyperglycemia: Hyperglycemia is a condition characterized by higher than normal levels of glucose (sugar) in the blood. It typically occurs when the body has too little insulin or when the body cannot use insulin effectively.
Insulin: Insulin is a hormone produced by the beta cells of the pancreatic islets in the endocrine pancreas, crucial for regulating blood glucose levels. It facilitates the uptake of glucose by cells, thereby lowering blood sugar.
Insulin: Insulin is a hormone produced by the pancreas that plays a crucial role in regulating blood glucose levels and facilitating the metabolism of carbohydrates, fats, and proteins in the body. It is essential for maintaining homeostasis, supporting the functions of human life, and ensuring the proper utilization of organic compounds necessary for human functioning.
Insulin Secretion: Insulin secretion is the process by which the pancreatic beta cells release the hormone insulin into the bloodstream. Insulin is a crucial regulator of glucose metabolism, playing a central role in the endocrine pancreas and overall glucose homeostasis.
Insulin-like growth factors (IGFs): Insulin-like Growth Factors are proteins with a high similarity to insulin that play a crucial role in childhood growth and continue to have anabolic effects in adults. They are produced by the liver upon stimulation by growth hormone (GH) and act on various tissues, contributing to growth and development.
Insulin-to-Glucagon Ratio: The insulin-to-glucagon ratio refers to the balance between the two key hormones produced by the endocrine pancreas, insulin and glucagon. This ratio is a critical regulator of blood glucose levels and overall metabolic homeostasis in the body.
Islets of Langerhans: The islets of Langerhans are clusters of hormone-producing cells found within the pancreas. They play a crucial role in regulating blood glucose levels and are a key component of the endocrine system.
Lipogenesis: Lipogenesis is the metabolic process by which acetyl-CoA is converted into fatty acids in the body, primarily occurring in the liver and adipose (fat) tissue. This process is critical for energy storage and cell membrane formation.
Lipogenesis: Lipogenesis is the metabolic process by which excess carbohydrates and proteins are converted into fat molecules, primarily triglycerides, for storage in adipose tissue. This process is crucial for maintaining energy balance and regulating lipid metabolism within the body.
Lipolysis: Lipolysis is the metabolic process by which triglycerides in fat cells are broken down into glycerol and free fatty acids, providing energy for the body. It occurs in the adipose tissue and is regulated by hormones such as insulin and adrenaline.
Lipolysis: Lipolysis is the process of breaking down stored fat, or triglycerides, into free fatty acids and glycerol. This process is crucial for providing the body with an alternative energy source when glucose is not readily available, and it occurs primarily in adipose tissue under the regulation of the autonomic nervous system and endocrine hormones.
Pancreas: The pancreas is a vital organ that serves both as an endocrine gland, producing important hormones like insulin and glucagon to regulate blood sugar levels, and as an exocrine gland, secreting pancreatic juice containing digestive enzymes into the small intestine. It plays a crucial role in digestion and metabolism.
Pancreatic islets: Pancreatic islets are clusters of cells in the pancreas that produce and secrete hormones directly into the bloodstream to regulate blood sugar levels. These cells are crucial for maintaining glucose homeostasis in the body.
Pancreatic Polypeptide: Pancreatic polypeptide (PP) is a hormone produced by the pancreatic islet cells that plays a role in regulating appetite and energy homeostasis. It is part of the endocrine functions of the pancreas and is also involved in the development and aging of the endocrine system.
PP cell: PP cells, also known as pancreatic polypeptide-producing cells, are a type of cell found in the islets of Langerhans in the pancreas that secrete pancreatic polypeptide. This hormone helps regulate both the exocrine and endocrine pancreas, affecting digestive processes.
PP Cells: PP cells, also known as pancreatic polypeptide cells, are a type of endocrine cell found in the pancreas. They are responsible for the production and secretion of the hormone pancreatic polypeptide, which plays a role in regulating various physiological processes related to the endocrine pancreas and digestion.
Somatostatin: Somatostatin is a hormone produced primarily in the hypothalamus and pancreas that plays a key role in regulating various physiological processes, including growth, hormone secretion, and metabolism. It is closely connected to the central control of the body, hormones, the pituitary gland and hypothalamus, the endocrine pancreas, and the development and aging of the endocrine system.
Type 1 Diabetes Mellitus: Type 1 diabetes mellitus is an autoimmune disorder in which the body's immune system mistakenly attacks and destroys the insulin-producing beta cells in the pancreas, leading to an absolute insulin deficiency and the inability to properly regulate blood glucose levels.
Type 2 Diabetes Mellitus: Type 2 diabetes mellitus is a chronic metabolic disorder characterized by the body's inability to effectively use insulin, a hormone responsible for regulating blood sugar levels. This leads to elevated blood glucose concentrations, which can have serious health consequences if left untreated.