Glucagon

Source of secretion:

It is secreted from Alpha cells in the islets of Langerhans of pancreas.

Chemistry:

It is a polypeptide with molecular weight of 3485. It contains 29 amino acids.

Synthesis:

It is synthesized from preprohormone called as prepro glucagon.

Metabolic roles of glucagon:

Action of glucagon are antagonistic of those of insulin. It increases the blood sugar level and regarded as hyperglycemic hormone.

It has various metabolic effect on carbohydrate, protein and fats which are illustrated as below:

1. Effect on carbohydrate metabolism:

• It increases glycogenolysis ( breakdown of glycogen into glucose). The glucose then are released from liver to blood.
• It also increases gluconeogenesis in liver by activating various enzymes of gluconeogenesis pathway.

2. Effect on lipid metabolism:

• It shows lipolytic effect ( breakdown of lipids to release free fatty acids). These fatty acids are used for the release of energy.

3. Effect on protein metabolism:

• It increases gluconeogenesis (formation of glucose from proteins or amino acids). This is done by increasing the transport of amino acids into liver cells.

Clinical conditions associated with insulin and glucagon

1. Diabetes mellitus

-type I (due to absence of beta cells and deficiency of insulin)

-type II ( due to less number of insulin receptors)

2. Hyperinsulinism – hypersecretion of insulin due to tumor of beta cells of pancreas.