Endocrine Pancreas and Hormone Function

These flashcards cover key concepts regarding the structure and function of the endocrine pancreas and its hormones, particularly insulin and glucagon, along with metabolic pathways.

What are the main hormones secreted by the pancreas?

Insulin, glucagon, somatostatin, pancreatic polypeptide.

What are the cell types found in the Islets of Langerhans?

α cells (glucagon), β cells (insulin), δ cells (somatostatin), and PP cells (pancreatic polypeptide).

What is the role of insulin in the body?

Insulin facilitates glucose uptake, promotes storage of glucose as glycogen, and inhibits glucose production.

What hormone stimulates the liver to convert glycogen into glucose?

Glucagon.

What is the primary function of somatostatin in the pancreas?

Somatostatin inhibits the release of insulin and glucagon.

How does insulin affect lipid metabolism?

Insulin promotes fatty acid synthesis and inhibits the breakdown of fats.

What triggers the secretion of glucagon?

Low blood glucose levels and specific amino acids.

What mechanism regulates the synthesis of insulin in β cells?

Insulin synthesis begins with the preproinsulin, which gets processed to proinsulin, and then to active insulin.

What effect does glucagon have on liver metabolism?

Glucagon increases blood glucose by promoting gluconeogenesis and glycogenolysis.

What is the role of glucose transporters like GLUT4?

GLUT4 facilitates glucose entry into muscle and fat cells in response to insulin.

How does insulin affect glycogen synthase?

Insulin activates glycogen synthase, promoting glycogen formation.

What is the relationship between insulin and hormone-sensitive lipase (HSL)?

Insulin inhibits HSL, reducing lipolysis.

What role does protein kinase play in the action of glucagon?

Glucagon activates protein kinase A (PKA), which promotes glycogen breakdown.

What metabolic effect does insulin have on amino acids?

Insulin promotes amino acid uptake and protein synthesis.

What is glucagon-like peptide-1 (GLP-1)?

GLP-1 is an incretin hormone that stimulates insulin secretion post-meal.

What role does acetyl-CoA carboxylase play in metabolism?

Acetyl-CoA carboxylase is crucial for fatty acid synthesis; it is activated by insulin and inhibited by glucagon.

Define glycogenolysis.

Glycogenolysis is the process of breaking down glycogen to release glucose.

What is the consequence of a deficiency in glucose-6-phosphatase?

It leads to Von Gierke’s disease, causing impaired glucose release from the liver.

How does McArdle syndrome affect muscle metabolism?

It impairs glycogen breakdown in muscles, leading to cramps and fatigue during exercise.

How does insulin signal its effects on target cells?

Insulin binds to its receptor, activating a signaling cascade that recruits GLUT4 to the cell membrane.

Beyond its secretion by PP cells, what is the recognized physiological role of pancreatic polypeptide (PP) concerning digestive functions and satiety?

Pancreatic polypeptide (PP) secretion is stimulated by food intake (especially protein-rich meals) and acts as an important satiety signal by reducing appetite. It also inhibits pancreatic exocrine secretion (digestive enzymes and bicarbonate) and gallbladder contraction, thus regulating nutrient digestion and absorption

Outline the molecular cascade initiated by glucagon binding to its G-protein coupled receptor on hepatocytes, leading to glucose release.

Glucagon binds to a G-protein coupled receptor (GPCR), activating an associated Gαs protein. This activates adenylyl cyclase, which catalyzes the conversion of ATP to cyclic AMP (cAMP). cAMPcAMP then activates protein kinase A (PKA), which phosphorylates key enzymes like glycogen phosphorylase (promoting glycogenolysis) and various enzymes in gluconeogenesis.

Explain the biological origin and clinical significance of C-peptide measurement in assessing pancreatic function

C-peptide is a 31-amino acid connecting peptide cleaved from proinsulin to yield mature insulin. Since it is secreted in equimolar amounts with insulin and has a longer half-life, its measurement provides a reliable indicator of endogenous insulin production (useful for differentiating Type 1 from Type 2 diabetes, or monitoring β-cell function in insulin-treated patients).

Detail the major downstream signaling pathways activated following insulin binding to its tyrosine kinase receptor, beyond simple glucose transporter recruitment.

Insulin binding causes autophosphorylation of the receptor, which then phosphorylates Insulin Receptor Substrate (IRS) proteins. These activated IRS proteins initiate two main pathways: the PI3K/Akt pathway (involved in glucose uptake, glycogen synthesis, protein synthesis, and cell growth) and the MAPK pathway (involved in cell growth and differentiation)

Describe the critical function of ATP-sensitive potassium channels (KATPKATP​ channels) in the regulation of glucose-stimulated insulin secretion from pancreatic β-cells

In pancreatic β cells, increased glucose metabolism leads to elevated intracellular ATP. This rise in ATP closes KATPKATP​ channels, causing membrane depolarization. Depolarization opens voltage-gated Ca2+Ca2+ channels, leading to Ca2+Ca2+ influx and exocytosis of insulin granules