Hormones secreted by pituitary gland, Biology

(a) Hormones of the Anterior lobe -

The anteriorIobe of the pituitary gland secretes the following hormones, most of them are trophic hormones.

(i) Somatotropic hormone or Growth hormone (STH or GH) or Somatotropin (Soma- body, trophe- nourishment). This hormone stimulates growth directly and in conjunction with other hormones. Growth hormone promotes protein anabolism, the absorption of calcium from the bowel and the conversion of glycogen to glucose. It is in highest concentration in the blood until the individual has reached his full status, but a continuous supply is necessary to stimulate the repair and replacement of body tissue throughout life. Secretion of the hormone is controlled by the hypothalamus.

Target Cells. Various body cells which undergo growth.

(ii) Thyroid stimulating hormone (TSH) or Thyrotropin. This hormone controls the growth and activity of the thyroid gland. It influences the uptake of iodine, the synthesis of the hormones, thyroxine and tri-iodothyronine by the thyroid gland and the release of stored hormones into the blood stream. The hypothalamus has a stimulating effect on the production of thyrotrophic hormone especially by increasing the secretion when the body is cold and decreasing secretion when it is hot.

Target Cells. Cells of thyroid.

(iii) Adrenocorticotropic hormone (ACTH). This hormone stimulates the cortex of the adrenal gland to produce its hormones. The amount of ACTH secreted depends upon the concentration of the hormones in the blood from the adrenal cortex and on stimulation of the pituitary gland by the hypothalamus. The latter's influence on the production of ACTH is particularly important during emotional and physical stress.

Target Cells. Cells of adrenal cortex.

(iv) Prolactin hormone (PRL) or Mammotrophin hormone (MTH) or Luteotrophic hormone (LTH). Prolactin is also called the "hormone of maternity" because its main physiological effect is to activate growth of breasts during pregnancy. The name luteotrophic hormone (LTH) refers to because it also stimulates the corpus luteum of the ovary to secrete progesterone hormone.

Target Cells. Cells of mammary glands.

(v) Gonadotropic hormones. These are as follows:

(a) Follicle-stimulating hormone (FSH). It stimulates growth of ovarian follicles and their secretion of oestrogens in the female, and spermatogenesis (formation of sperms) in the male.

(b) Luteinizing hormone (LH). In female it stimulates the corpus luteum of the ovary to secrete progesterone. In male it activates the Leydig's (interstitial) cells of the testes to secret androgenes hence it may be called interstitial cell stimulating hormone (ICSH) in male.

Target Cells. Cells of gonads (testes and ovaries).

(b)      Hormone of the Intermediate lobe

Melanocyte stimulating hormone (MSH) or intermedin causes dispersal of pigment granules in the pigment cells, thereby darkening the colour in certain animals like fishes and amphibians. It is believed that it is associated with the growth and development of melanocytes in man which give colour to the skin.

Target Cells. Melanocytes in skin.

(c)      Hormones of the Posterior lobe

(i) Oxytocin (OT; Pitocin) - Oxytocin promotes contraction of the uterine muscle or labour pain and contraction of the myoepithelial cells of the lactating breast, squeezing milk into the large ducts behind the nipple. In late pregnancy the uterus becomes very sensitive to oxytocin. The amount secreted is increased just before and during labour and by sucking of the baby. Because of its role, oxytocin is called "birth hormone" and "milk ejecting hormone".

Target Cells. Cells of mammary glands.

(ii) Antidiuretic hormone (ADH) or Vasopressin or Pitressin. This hormone has two main functions.

(a) Antidiuretic effect. It increases the reabsorption of water in the distal convoluted tubule, collecting tubules and collecting ducts of the nephrons of the kidneys. As a result, the reabsorption of water from the glomerular filtrate is increased.

(b) Pressor effect. Involuntary muscles in the walls of the intestine, gall bladder, urinary bladder and blood vessels are stimulated to contract by ADH. Contraction of the walls of the blood vessels raises the blood pressure and this may be its most important pressor effect.

Target Cells. Cells of kidneys.

Note :- The pituitary gland was called as "Master Endocrine Gland" of body or the "Chief Executive of Endocrine System" or "The Leader of Endocrine Orchestra" as it secretes the number of hormones (e.g., TSH, ACTH etc.) which regulate the working of other endocrine glands. But it is not proper to call it as master endocrine gland because it is itself under the control of the releasing hormones secreted by the hypothalamus of the brain. Thus the hypothalamus is, in fact, the supreme commander of endocrine regulation and master endocrine gland.

Posted Date: 10/2/2012 6:38:30 AM | Location : United States







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