physiology of pancrease Flashcards
(104 cards)
1. Where is the pancreas located in the body?
Retroperitoneal; behind the stomach.
- What is the composition of the exocrine part of the pancreas?
The exocrine part is made up of acini, constituting 99% of the pancreas volume, and it releases pancreatic juice rich in digestive enzymes and bicarbonates.
- What makes up the endocrine part of the pancreas, and what percentage of the pancreas volume does it constitute?
The endocrine part is made up of Islets of Langerhans, constituting 1% of the pancreas volume.
- Name the different cells found in the Islets of Langerhans.
- Alpha cells (produce glucagon) - Beta cells (produce insulin) - Delta cells (produce somatostatin) -
- F cells (PP cells, produce pancreatic polypeptide hormone)
- What hormone is secreted by alpha cells, and what stimulates its secretion?
Glucagon is secreted by alpha cells. It is stimulated by low blood glucose levels (hypoglycemia, below 70-80 mg/dl) and sympathetic nervous system hormones (epinephrine and norepinephrine).
- Name the inhibitors of glucagon secretion.
Hormones produced by the intestine: Cholecystokinin and Secretin.
- What are the effects of glucagon on blood glucose levels?
Increases blood glucose levels by promoting gluconeogenesis and glycogenolysis in the liver, as well as lipolysis in adipose tissue.
- What hormone is secreted by beta cells, and what stimulates its secretion?
Insulin is secreted by beta cells. It is stimulated by high blood glucose levels (hyperglycemia, above 120-130 mg/dl).
- What are the effects of insulin on blood glucose levels?
Decreases blood glucose levels by promoting glycogenesis in the liver, lipogenesis in adipose tissue, and increased glucose uptake viaGLUT-4 in adipose tissue and muscles.
- Provide an example of hormone antagonism.
Glucagon and insulin have opposing effects and exhibit antagonism.
- Provide an example of hormone synergism.
Epinephrine and norepinephrine have similar effects and exhibit synergism.
- What is permissiveness in the context of hormone interactions?
Permissiveness occurs when one hormone needs to be present for another hormone to function. An example is that thyroid hormone is required for certain types of sex hormones to cause brain development.
- What is the process of gene expression in α-cells?
Inside the DNA of α-cells, a specific gene undergoes transcription, leading to the synthesis of mRNA. mRNA is then translated by ribosomes in the cytoplasm, producing the protein proglucagon. Proglucagon undergoes modifications in the rough endoplasmic reticulum, becomes glucagon in the Golgi apparatus, and is packaged into vesicles. These vesicles release fully packaged glucagon.
- How do alpha cells respond to hypoglycemia?
Alpha cells respond to hypoglycemia by allowing glucose entry through GLUT-1 transporters. Glucose undergoes glycolysis, leading to the production of pyruvate and acetyl-CoA, which enters the Krebs cycle. NADH and FADH2 are produced, and through oxidative phosphorylation, ATP is generated in the mitochondria. This process helps increase ATP levels in the cell.
- Explain the role of K+ channels in glucose regulation.
K+ channels on the cell membrane bind ATP. With low ATP levels (resulting from low glucose), the channels close less tightly, allowing some K+ ions to exit. The cell becomes less positive, leading to less membrane depolarization. With high ATP levels (resulting from high glucose), the channels close tightly, making the cell extremely positive, causing membrane depolarization and opening of calcium channels.
- How does glucagon synthesis lead to increased blood glucose?
Specific proteins on vesicles containing glucagon and the cell membrane,linked by Ca++, facilitate fusion. This fusion releases glucagon into the blood, raising glucose levels during fasting or post-absorptive states when glucose is needed by the brain and other tissues.
- What is the role of glucagon in the liver?
Glucagon activates adenylate cyclase through a G stimulatory protein. Adenylate cyclase produces cAMP, activating protein kinase A (pkA). pkA then stimulates glycogen phosphorylase, promoting glycogenolysis (conversion of glycogen to glucose) and activates enzymes for gluconeogenesis, converting glycerol, amino acids, and odd chain fatty acids into glucose. The elevated glucose is released into the blood.
- What is the initial step in glucagon’s effect on the adipose tissue?
Glucagon activates a G stimulatory protein that binds to Adenylate cyclase on the cell membrane, resulting in the activation of the effector enzyme.
- Describe the role of Adenylate cyclase in the adipose tissue.
Adenylate cyclase, activated by glucagon, has a specific enzyme called GTPase. GTPase converts GTP to GDP, producing energy that is used to convert ATP to cAMP. cAMP then activates protein kinase A (pkA).
- What happens during Lipolysis in response to glucagon?
Glucagon-induced activation of pkA leads to the phosphorylation of hormone-sensitive lipase (HSL). Activated HSL breaks ester bonds in triacylglycerol (TAG), producing glycerol (sent to the liver) and fatty acids.
- How does glucagon affect the adipose tissue?
Glucagon promotes lipolysis in adipose tissue by activating HSL, resulting in the breakdown of TAG into glycerol and fatty acids. This process is illustrated in Figure 4.
- What is the initial step in glucagon’s effect on the myocardium?
Glucagon activates a G stimulatory protein that binds to Adenylate cyclase on the cell membrane, leading to the activation of the effector enzyme.
- What role does cAMP play in the myocardium’s response to glucagon?
cAMP, produced by Adenylate cyclase in response to glucagon, activates** protein kinase A (pkA)** in the myocardium.
- How does activated pkA influence calcium channels in the myocardium?
Activated pkA opens specific Ca++ channels in the myocardium, leading to an increase in Ca++ levels within the cells.