Insulin has three basic effects on carbohydrate metabolism:
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(i) Increased rate of carbohydrate (glucose) metabolism
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(ii) Decreased blood glucose concentration and
(iii) Increased glycogen stores in the tissues.
The ability of insulin to increase the rate of glucose metabolism in the tissues is very important to the body.
Its complete lack in the body may results in diabetes mellitus, a disease characterized by the following symptoms’:
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1. Hyperglycemia “(i.e., high blood sugar level) and glycosuria (i.e., sugar in urine) are common.
2. Diuresis (i.e., increased flow of urine) is common.
3. In liver glycogen levels may be below normal but muscle glycogen in general may be about normal, and heart muscle glycogen level is much above normal.
4. The conversion of carbohydrates into fat is reduced.
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5. The formation of glucose from non-carbohydrate sources (mostly protein) is increased to a great extent.
Effect of insulin on blood glucose concentration : In the deficiency of insulin, very little of the glucose absorbed from the gastrointestinal tract is transported into the tissues with the result the blood sugar or glucose concentration is raised from a normal value of 90 mg per 100 ml to as high as 300 to 1200 mg per 100 ml.
On the other hand in the over production of insulin glucose is transported into the tissues so rapidly that its concentration in the blood falls to as low as 20 to 30 mg per 100 ml.
Effect on protein metabolism:
The total quantity of proteins stored in the tissues of the body is increased by insulin and greatly decreased by insulin deficiency, thus, insulin promotes protein meta bolism.
Effect of insulin on growth:
Insulin is essential for growth of animal. In the absence of insulin growth hormone has almost no effect in promoting growth of an animal.
Glucagon:
The other hormone of the islets is glucagon which is secreted by the a-cells. It is secreted in response to hypoglycemia.
Glucagon, like insulin, is a polypeptide of 29 amino acids and has a molecular weight of 3,485.