HORMONES OF PANCREASE INSULIN This is a polypeptide

HORMONES OF PANCREASE

• INSULIN • This is a polypeptide hormone synthesized from the β-cell of I slets Langerhans of the pancreas. It is synthesized as a large precursor called pre-proinsulin, which has 109 A. A. It is immediately converted into pro-insulin in the endoplasmic reticulum by removal of 23 A. A. (86 A. A). The pro-insulin is transported to the Golgi apparatus which cleave to form insulin and C-peptide. The C-peptide contains 33 A. A and the insulin contains 53 A. A from which 2 A. As are cleaved to form insulin with 51 A. As

• Human insulin contains 51 A. As arranged in 2 polypeptide chains namely α chain(21 A. A) and β chain(30 A. A). 2 types of disulfide bonds. • The insulin formed is packed into granules in the Golgi apparatus with two zinc ions and one calcium ion. By exocytosis , these insulin granules are released into the circulation along with C-peptide • Both C-peptide and insulin are produced in equimolar concentrations. • C-peptide has no biological activity.

Insulin mainly controls blood glucose by the following mechanisms: 1 - Increases the uptake of glucose by the peripheral. 2 - Increases the utilization of glucose by stimulates. 3 - Stimulates glycogenesis and inhibits glycogenolysis. 4 - Inhibits lipolysis. 5 - Inhibits gluconeogenesis.

• Degradation of insulin • Insulin is rapidly degraded in the liver , the half -life of insulin in the plasma is 4 to 5 minutes. Insulin is mainly cleaved by insulinase and hepatic glutathione transdehydrogenase. • Effect on carbohydrate metabolism: • Insulin increases the uptake of glucose by • 1 -Skeletal , cardiac and smooth muscles • 2 - Adipose tissue • 3 - Leucocytes and Mammary glands

• About 80% of the glucose uptake in the body is not dependent on insulin. • About 50% of glucose ingested is utilized to meet the energy needs of the body through glycolysis , 40% glucose converted into fat and the remaining 10% is converted into glycogen. • Insulin enhances the synthesis of TG and inhibit lipolysis and ketogenesis • Insulin increases protein synthesis by increasing the uptake of A. A into the cells. Insulin promotes cell growth and replication

• Stimulation of insulin secretion • Glucose and amino acids • Pancreatic and gastrointestinal hormones like - Glucagon , Gastrin , Secretin and pancreozymin Inhibitors of insulin release Hypoglycemia Somatostatin and many drugs like β-adrenergic blockers Diazoxide and Nicotinic acid