GLUCAGON ::
Glucagon is chemically polypeptide containing 29 amino acids with a molecular weight of 3450 It raises blood glucose level by (1) promoting glucogenolysis (break -down of glycogen into glucose ) and by (2) stimulating glyconeogenesis (formation of glucose from non -carbohydrate source) Glucagon activates adenylate cyclase to form cyclic AMP and accelerates deamination of amino acids It also has a calorigenic action Glucagon does not produce any action on either muscle glycogen or on the peripheral utilization of glucose It promotes lipolysis in adipose tissue and liver and enhances ketogenesis
The main stimulus for the secretion of glucagon is a fall in blood glucose level The rise in blood glucose inhibits secretion of glucagon During starvation glucagon and growth hormone maintain the blood glucose level A rise in plasma free fatty acids provides extra energy for most tissues but the glucose level in the blood must be maintained to provide the brain with adequate amounts of energy since glucose is the only substance which the brain can utilize for energy production
Insulin ::
Insulin is also a polypeptide hormone containing 51 amino acids arranged in two chains the chain A containing 21 amino acids and the chain B containing 30 amino acid residues These two chains are cross linked by two sulphur bridges between cysteine residues Insulin is formed by proteolytic cleavage of its 84 amino acid precursor proinsulin
Insulin circulates in the blood plasma bound to a B-globulin It is inactivated in the body by the enzyme glutathion insulin transhydrogenase which breaks up the bisulfide bridges to form two peptide chains A and B
A normal man secretes about 50 units of insulin daily The total insulin content of pancreas is about 200 units Insulin secretion is continuous but its rate of secretion is influenced by a variety of factors
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