Hormonal Control of Carbohydrate Metabolism

Hormonal Control of Carbohydrate Metabolism:

The supply of glucose to the blood by the liver and its utilization in the tissues must be regulated for the ‘smooth’ functioning of the metabolic processes in the body. Hormones secreted by the endo-organs play an important role in the metabolism. They can be classed into two varieties:

• Those which regulate normal function and are essential for carbohydrate metabolism.
• Those which influence and are not essential for carbohydrate metabolism.

Insulin- Insulin administration decreases the release of glucose to the systemic blood by the liver, and increases the rate of utilization of glucose by tissue cells. The blood glucose level falls because of decreased glycogenolysis or increased hepatic glycogenesis. The synthesis of glucose from proteins is also decreased. In the liver which is freely permeable to glucose, insulin exerts a regulatory influence upon the activity of glucokinase.

Adrenal Cortical Hormones- Adrenal oxy-steroid hormones increase the blood sugar level, liver glycogen, and total body carbohydrate. These hormones influence by increasing the output of glucose by the liver and decreasing the utilization of glucose by the tissues. The synthesis of carbohydrates from protein is also increased by the stimulation of the activity of certain transaminases.

Adrenohypophyseal Factors- The adrenocorticotrophic hormones (ACTH) and thyroid-stimulating hormones increase the secretions of the adrenal cortex and thyroid glands by stimulating them, which in their turn affects the carbohydrate metabolism. Anterior pituitary extracts increase blood sugar and decrease the respiratory quotient. These ‘diabetic’ symptoms are due to somatotropin which depresses the utilization of glucose.

Epinephrine- The action of epinephrine is to increase blood sugar and lactic acid, which is due to an increase in the rate of glycogenolysis in the liver and muscles. Epinephrine stimulates phosphorylase activity and diminishes the uptake of glucose by tissue cells.

Thyroxine– The thyroid hormone increases the breakdown of glycogen and thereby the blood sugar. Thyroxine also increases the absorption of hexoses from the intestine.

Glucagon- The physiological importance of this substance is not known. It is produced by the α-cells of islets of Langerhans and causes an increase in blood sugar by accelerating hepatic glycogen breakdown.