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Pituitary Gland Hormones and their physiological effects pituitary gland (hypophysis) Often called the "Master Gland," the pituitary gland lies in the sella turcica at the base of the skull. It is a small endocrine organ that is controlled by the hypothalamus, and directs other organs and endocrine glands to suppress or induce hormone production. Structure of the pituitary gland The anterior lobe (or adenohypophysis) The intermediate / middle lobe The posterior lobe (or neurohypophysis) Intermediate Lobe anterior pituitary Human growth hormone (HGH) Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Prolactin (PRL) Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) Intermediate pituitary Melanocyte stimulating Hormone (MSH) posterior pituitary Antidiuretic Oxytocin hormone (ADH) Anterior Pituitary Hormones Growth Hormone (GH): GH stimulates overall protein synthesis with an associated retention of phosphorous probably by increasing tubular reabsorption. GH increases DNA & RNA synthesis It increases the synthesis of collagen GH brings about “Lipolysis” in a mild way by mobilizing fatty acids from adipose tissue by activating the hormone sensitive “triacylglycerol lipase”. Hypersecretion of GH can result in hyperglycemia, poor sugar tolerance and glycosuria. Abnormalities of GH Panhypopitutarism: It is due to decreased secretion of all the anterior pituitary gland hormones. It may be congenital (or) ii may occur suddenly during the life of the individual. Dwarfism: It is due to deficiency of anterior pituitary gland secretion during childhood. Levi-lorain dwarfism: It is due to hereditary inability to form somatomedin C, but the rate of GH secretion. Acromegalay: It is due to increased secretion of GH. AdrenoCorticoTrophic hormone (ACTH): ACTH increases the synthesis of corticosteroids by the adrenal cortex and also stimulates their release from the gland. ACTH is found to increase the transfer of cholesterol from plasma lipoproteins into the fasciculata cells. The ACTH induces rise in cAMP, brings about phosphoryl and activation of “Choleseryl esterase” the enzyme action ultimately makes a large pool of free cholesterol. It activates the rate-limiting enzyme for conversion of cholesterol to pregnenolone (Cholesterol desmolase) . It activates dehydrogenases of HMP to increase the concentration of NADPH required for hydroxylation. It activates “Hormone-sensitive lipase”, which is involved in lipolysis which increases the level of free fatty acids. Abnormalities of ACTH Cushing’s disease: Over secretion of ACTH leads to cushing’s disease, because of tumor (or) hyperplasia of βcells of the anterior pituitary gland lobe. This leads to hypersecretion of corticosteroids specially glucocortucoids. This produces symptoms like hyperglycemia, glycosuria, muscle wasting, atrophy of skin, high urinary negative nitrogen balance. Abnormal retention of fats giving moon shape face appearance, retention of Na + and water and hypertension. Leutinizing Hormone: In females: It causes the final maturation of graffian follicles and stimulates ovulation. Stimulates secretion of estrogen by the THECA and Grannulosa cells. It helps in the formation and development of corpus lutem for leutinization of cells. In the ovary it can stimulate the non-germinal elements, which contain the interstitial cells to produce the androgenes, androstenedione, DHEA and testosterone. Follicle Stimulating Hormone (FSH): It brings about its action by specific receptor binding and cAMP In Females: It promotes follicular growth Prepares the graffian follicle for the action of LH. Enhances the elease of estrogen induces by LH. In Males: It stimulates seminal tubular and testicular growth. Plays an important role in maturation of spermatozoa. Thyroid Stimulating Hormone (TSH): It stimulates the activity of thyroid gland and enhances the rate of certain reactions, such as, Removal of iodine form blood by thyroid. Conversion of iodide to thyroid hormones. Release of hormonal iodide from thyroid. Intermediate pituitary Hormones Melanocyte stimulating Hormone (MSH): MSH darkens the skin and is involved in skin pigmentation by deposition of mammalian by melanocytes. Abnormality: Addison’s disease: MSH is in excess, which increases the synthesis of melanin resulting in brown pigmentation of skin. Such a condition occurs in this disease. Posterior Pituitary Hormones Antidiuresis: Vasopressin causes “Antidiuresis”. It increases the permeability of the collecting ducts and tubules to water and allows most of the water to be reabsorbed as the tubular fluid passes through these ducts, there by conserving water in the body and producing very concentrated urine. Urea-retention effect: Permeability of meduallry collecting dusts to urea is increases by vasopressin. This leads to retention of urea and subsequently contributes to hypertonicity of the medullary intersitium. Pressor effect: It stimulates the contraction of smooth muscles and thus causes vasoconstiction by increasing cytosolic Ca +2 concentration. Glycogenolytic effect: By increasing intracellular Ca +2 concentration, it causes glycogenolysis. Abnormality: Deficiency of ADH leads to “Diabetes insipidus”, it is characterized by excretion of large volumes of dilute urine. Excess secretion of ADH often results from ectopic production of ADH by malignant tumors, referred to as the “Syndrome of Inappropriate secretion of ADH” (SIADH). There is hypotonic expansion of extracellular volume, with hyponatremia. Oxytocin: Function: Oxytocin mainly causes smooth muscle contraction. a) Effect on the uterus and on birth: Oxytocin causes the contraction of the pregnant uterus especially toward the end of gestation and is partially responsible for effecting birth. b) Effect of oxytocin on milk ejection: Oxytocin has an effect on the mammary gland. Suckling generates a neurogenic reflex, which stimulates the production of oxytocin of oxytocin. It causes contraction of the myoepithelial called expelling the milk into milk ducts from the acinii. THE END