Insulin And. Glucagon DLA

Question 1

What are the hormone producing cell types of the islets of langerhans?

Answer 1

• Beta cells (70% ): Release insulin which lowers blood glucose level • Stimulates synthesis of glycogen, protein and fatty acids.
• Alpha cells (20% ): Release glucagon which increases the blood glucose level • Stimulates glycogen breakdown and gluconeogenesis in liver and kidney
• Delta cells (10% ): Release somatostatin which inhibits release of both insulin and glucagon in the islets (paracrine).
• F-(PP) cells (5% ): Release pancreatic polypeptide hormone which inhibits pancreatic exocrine secretions. Also, may act as a satiety hormone.

Question 2

Summarize mechanism of insulin release

Answer 2

1. Increased glucose entry into beta-cells (via GLUT-2) →Activates Glucokinase uses glucose for ATP formation
2. Increased plasma glucose levels→Increases ATP levels→ Close ATP-sensitive K+ channels
3. Membrane depolarization→ Calcium influx
4. High intracellular calcium levels trigger release of insulin and C-peptide (ratio 1:1) from granules

Question 3

What are the mechanism of action on target cells?

Answer 3

Insulin receptor: intrinsic tyrosine kinase activity

Question 4

What are the effects of insulin on the liver?

Answer 4

• Liver receives nutrients from intestine via portal vein containing dietary monosaccharides.
• Activates glycogen synthesis and glycolysis in liver. Hence, increases utilization of glucose by liver
• Stimulates hepatic synthesis of fatty acids, TAGs and cholesterol and release of VLDL into blood.
• Insulin lowers plasma glucose after a meal

Question 5

What are the effects of insulin on skeletal muscle?

Answer 5

• Increases Glucose uptake from blood (via GLUT-4)
• Activates Glycogen synthesis and glycolysis.
• Increases synthesis of sodium/potassium ATPase.
• Activates Amino acid uptake from blood
• Increases muscle protein synthesis (anabolic)

Question 6

What are the effects of insulin on adipose tissue?

Answer 6

Increased plasma glucose level—> high serum insulin/glucagon ratio—> increased glucose uptake (GLUT-4)—> increases uptake of fatty acids and glucose resulting in TAG synthesis increased

High serum insulin/glucagon ratio — > lipoprotein lipase forms free fatty acids in blood (Cleaves TAG in VLDL and chylomicrons) —> increases uptake of fatty acids and glucose resulting in TAG synthesis

Increase in TAG synthesis and TAG storage in fat cells

Question 7

What is glucagon?

Answer 7

• Peptide hormone

* In a-cells of pancreas, proglucagon converted to glucagon by proteolytic cleavage

Question 8

What are the activators of glucagon secretion from alpha cells?

Answer 8

Activators:
Low blood glucose level (Below 70 mg/dL or 3.8 mM)
Amino acids
Epinephrine and norepinephrine
Cortisol
Neural input: Sympathetic stimulation during stress

Question 9

What are the inhibitory factors that prevent secretion of glucagon from alpha cells?

Answer 9

Inhibitory:
Increased blood glucose Insulin
Somatostatin

Question 10

What is the mechanism of action of glucagon?

Answer 10

Glucagon binds to G protein-coupled receptors (GPCR) and acts via cAMP- messenger system

2. a-subunit exchanges GDP for GTP
3. Increased cAMP activates PKA
4. Phosphorylates downstream enzymes activated catabolic processes while inhibiting anabolic processes

Question 11

What are the effects of glucagon target tissues and actions?

Answer 11

• Glucagon receptors: hepatocytes and renal cortex cells.
• Glucagon activates glycogen degradation and gluconeogenesis in liver and in kidney. Increases glucose release into blood
• Increases plasma glucose level
• In liver: Inhibits glycogen synthesis, glycolysis, fatty acid synthesis and cholesterol synthesis.