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 2A.As are cleaved to form insulin with 51 A.As

Human insulin contains 51 A.As arranged in 2 polypeptide chains namely α chain(21A.A) and β chain(30A.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