Physiology of Pancreas: Glucagon

Glucagon

• Secreted by

• Transported

  • By

  • To

• Stimulated by

Secreted by: α-cells in pancreas

Transported

• By: Hepatic portal system

• To: Liver

Stimulated by: Lowering of glucose concentration

Mechanism of Action of Glucagon

• Metabolic role

• What is gluconeogensis

• To stimulate glycogenolysis, which liver enzyme does glucagon activate

• Effect on glycogen stores

• Enzyme that converts glucose-6-phosphate into free glucose

• How does affect glucose-6-phosphatase activity

• What second messenger is used in glucagon’s mechanism of action

Metabolic role: Glucagon raises blood glucose by stimulating glycogenolysis and gluconeogenesis, mainly in the liver.

What is gluconeogensis: Synthesis of new glucose from non-carbohydrate sources

To stimulate glycogenolysis, which liver enzyme does glucagon activate: Glucagon activates hepatic phosphorylase, which promotes glycogen breakdown

Effect on glycogen stores: Glucagon stimulates the breakdown of glycogen and simultaneously prevents new glycogen formation

Enzyme that converts glucose-6-phosphate into free glucose: Glucose-6-phosphatase converts glucose-6-phosphate into free glucose that can enter the bloodstream

How does affect glucose-6-phosphatase activity: Increases glucose-6-phosphatase activity by increasing cAMP levels

What second messenger is used in glucagon’s mechanism of action: cAMP

How does these factors regulate glucagon secretion

• Plasma glucagon concentration

• Calcium ions

• Amino acids

• Fatty acids

• Digestive hormones

• Nervous control

Plasma glucagon concentration: Increase in glucose due to glucagon activity inhbits its secretion

Calcium ions: Required for the secretion

Amino acids: AA like

• alanine stimulate glucagon secretion

• Arginine stimulate both glucagon and insulin

• Leucine stimulates insulin secretion only

Fatty acids: High concentrations of free fatty acids inhibit glucagon secretion

Digestive hormones:

• Pancreozymin stimulates

• Secretin inhibits

Nervous control:

• Sympahtic stimulation increases

• Heavy exercise increases

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