Wk 8 Flashcards
Endocrine Function of the Pancreas and Diabetes Mellitus (30 cards)
What is the role of the Islets of Langerhans?
Endocrine cells that secrete pancreatic hormones.
What are the five cell types of the Islets of Langerhans and what do they secrete?
- Alpha cells - secrete glucagon
- Beta cells - secrete insulin, amylin
- Delta cells - secrete somatostatin
- PP cells - pancreatic polypeptide
- Epsilon cells - ghrelin
How are the hormones regulated?
Somatostatin - inhibits alpha & beta (glucagon & insulin)
Insulin - inhibits alpha (glucagon)
Glucagon - stimulates beta (insulin)
Ghrelin - inhibits alpha and beta (glucagon & alpha)
What are the effects of insulin of carbohydrate metabolism?
Promotes uptake and storage of glucose.
What are the effects of insulin of protein metabolism?
Promotes protein synthesis.
What are the effects of insulin of fat metabolism?
Promotes fat storage.
What is the biosynthesis pathway of insulin (beta cells)?
Preproinsulin –> proinsulin –> insulin & C-peptide
What is C peptide used for?
Used as a useful marker of beta-cell function (more C peptide = greater insulin secretion in blood).
What are the steps for the process of insulin secretion?
- Glucose transported by facilitated diffusion into beta cells via GLUT-2
- Increase in glucose conc. (beta cells)
- Increase in glucose metabolism (beta cells)
- Increase in ATP:ADP ratio within cell
- K+ channels close (depolarises cell)
- Ca2+ channels on membrane open
- Influx of extracellular Ca2+ ions
- Insulin released by exocytosis
What are the three main effector organs for insulin?
- Liver cells
- Muscle cells
- Adipose tissue
What is the role of insulin in the liver cells?
- increased metabolism of glucose as fuel
- increased storage of glucose as glycogen
- stimulates hepatic protein synthesis
- inhibits protein breakdown
What is the effect of insulin in the muscle cells?
- increased glucose uptake through GLUT4
What is the effect of insulin in adipose tissue?
- stimulates glucose uptake in adipose tissue via GLUT 4
- increases glucose storage as a triglyceride within the adipocytes
What is glucagon?
- secreted by alpha cells (Islets of Langerhans)
- antagonises insulin to increase blood glucose (causes hyperglycemia)
- target organ is the liver
What regulates glucagon?
Stimulated - hypoglycemia (low BG)
Inhibited - hyperglycemia (high BG)
What are the actions of glucagon?
- breakdown of liver glycogen
- increases gluconeogenesis
- inhibits storage of triglycerides
- increases fatty acids (ketogenic)
What are the actions of glucagon in the liver?
- increased glycogenolysis (breakdown of glycogen)
- increased gluconeogenesis
(formation of glucose from non-carbohydrates)
What are the actions of glucagon in the adipose tissue?
- increased lipolysis (breakdown of fats)
What is the mechanism of action of glucagon?
Glucagon activates G protein stimulating adenylate cyclase (cAMP pathway).
What are incretins?
Digestive tract hormones that increase insulin secretion from beta cells in pancreas.
What are the two major incretins?
- Glucagon-like peptide 1 (GLP-1)
- Glucose-dependant insulinotropic polypeptide (GIP)
What is the main action of GLP-1?
Stimulation of glucose-dependant insulin release from the pancreatic islets.
What is the main action of GIP?
In fasting state - enhances glucagon activity (wants to increase BG as it is low).
During hyperglycemia - maintains BG level.
What are the hormones that regulate blood glucose conc?
Insulin & Glucagon
Fed state:
- insulin dominates (lowers BS)
Fasting state:
- glucagon dominates (raises BS)
