Write short notes on the functions of the following hormones,

(a) Parathyroid hormone (PTH) – The parathyroid hormone is secreted by the parathyroid gland. Its main function is to increase the level of calcium in blood. It promotes the reabsorption of calcium from nephrons and also, promotes the absorption of calcium from digested food. Hence, it plays an important role in maintaining calcium balance in the body.

(b) Thyroid hormones – Thyroid hormones such as thyroxine, triiodothyronin, and thyrocalcitonin are secreted by the thyroid gland.

Thyroxine maintains the basal metabolic rate of the body and regulates the carbohydrate, fat, and protein metabolism. Water and electrolyte balance is also maintained by thyroid hormones. Thyrocalcitonin or calcitonin lowers calcium level in blood plasma. It plays a significant role in calcium levels along with parathyroid hormone.

(c) Thymosins – Thymosin is secreted by the thymus gland. It plays a major role in protecting the body against infectious agents. It helps in the differentiation of T-lymphocytes and also promotes the reproduction of antibodies. Hence, it provides both cell-mediated and humoral immunity. Thymosins also help in the development of sex glands.

(d) Androgens – The leydig cells of testis produce androgens such as testosterone. Testosterone is a male sex hormone that regulates the development of secondary sex characteristics such as facial hair, hoarse voice, development of reproductive organ, etc. Androgens also regulate the development, maturation, and functions of various male accessory organs such as epididymis and prostate glands. It stimulates spermatogenesis and formation of mature sperms. It also influences male sexual behaviour.

(e) Estrogens­­- Estrogen is the female sex hormone that controls the development of secondary sex characteristics such as enlargement of breasts and development of female reproductive organs. It plays a role in the development, growth and maturation of female secondary characteristics. It also helps in the development of growing ovarian follicles. It influences female sexual behaviour.

(f) Insulin and glucagon – Glucagon and insulin are secreted by cells of pancreas. They regulate the blood glucose level in the body. α-cells secrete glucagon that maintain a normal blood glucose level in the body, whereas β-cells secrete insulin that regulates the storage of glycogen in the liver.

Function of insulin – Insulin stimulates glycogenesis (conversion of glucose to glycogen). The rapid conversion of glucose from the blood to glycogen in hepatocytes and adipocytes results into a decreased glucose level. Insulin also prevents the formation of glucose from non-carbohydrate substances such as proteins and fats. Hence, it acts as a regulator of carbohydrate metabolism.

Function of glucagon – The main function of the glucagon is to increase the level of glucose when there is a deficiency of glucose in the body. This process is known as glycogenolysis.