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Anterior pituitary hormones Growth hormone (GH)(Somatotropin) Factors affecting GH secretion Gonadotrophic hormones Follicle stimulating hormone (FSH) Luteinizing hormone ( LH or ICSH) Prolactin Hormones of the middle lobe of the pituitary gland Actions of MSH Posterior pituitary hormones Vasopressin Oxytocin Pituitary gland The pituitary gland comprises the embryologically and functionally distinct anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis). The anterior pituitary hormones and their corresponding regulatory hormones/factors are described in detail below. Secretion of most of the hormones of the anterior pituitary is under the control of the hypothalamus. Secretion also controlled by the rate of secretion of endocrine gland through negative feedback mechanism. Growth hormone (GH)(Somatotropin) This hormone affects the growth. GH is also known as somatotrophic hormone or somatotropin hormone. It causes the growth of all tissues of the body that are capable of growing. It promotes both, i.e., the size of the cell and increase mitosis with the development of the increased number of cell. The hyposecretion of GH causes the dwarfism. The hyposecretion of GH causes the gigantism. Normal plasma concentration (adult) 3μg /L. (Children) 5μg /L. GH does not affect directly the cartilage and bones. However, GH indirectly stimulate their growth with help of several small proteins , collectively known as somatomedin which mainly synthesized in liver.(IGF-1) • Somatomedin is required for deposition of chondroitin sulphates and collagen, both of which are necessary for the growth of cartilage and bones. • GH increases protein synthesis. • GH increases the formation of RNA . • GH is also responsible to increase fat utilization for energy purposes . • GH increases conversion of glucose to glycogen. • GH increases blood glucose. Factors affecting GH secretion stimulants Exercise . Onset of deep sleep. Hypoglycemia. Protein meal. I.V. infusion of amino acids. Stress (arterial puncture ,surgery, endotoxin, vasopressin. Glucagon Laevo (-)Dopa Malnutrition β-adrenergic blockade. Inhibitants Hyperglycemia. Obesity. Hypothyroidism. Third trimester of pregnancy. High dose of glucocorticoids. α-adrenergic blockade. Thyroid stimulating hormone (TSH) TSH is glycoprotein secreted by basophilic staining cells of the anterior-pituitary. It has molecular weight of about 28,000. TSH stimulates secretion of thyroxine and other iodothyronines. TSH increases oxygen utilization, glucose uptake and oxidation processes. TSH stimulates adenyl cyclase activity and increases the tissue levels of c-AMP. Adrenocorticotropic hormone (ACTH) ACTH is also known as Corneotropin. ACTH is polypeptide consisting of 39 amino acids. It is secretes under control of crotitropin releasing hormone(CRH), of the hypothalamus. ACTH stimulates the synthesis of cortisol and 17-ketosteroids by adrenal cortex. ACTH is also necessary to maintain adrenocortical size, structure and vascularity. The action of ACTH is mediated by c-AMP. ACTH promotes insulin secretion from β-cells of pancreas. Gonadotrophic hormones Anterior pituitary secretes 3 gonadotrophic hormones: 1) Follicle stimulating hormone (FSH). 2) Luteinizing hormone or interstitial cell stimulating hormone ( LH or ICSH). 3) Prolactin or mammotropin (lactogenic hormone). All are water soluble glycoprotein except prolactin (simple protein). The hypothalamus control the secretion of gonadotrophic hormones by releasing factors. The releasing factors of FSH and LH exert inhibitory effects on the release of prolactin. Follicle stimulating hormone (FSH) FSH is found in plasma of both males and females. FSH stimulates the maturation and growth of ovarian follicles. The cyclic AMP formation is increased in these target tissue. In males, FSH causes the growth of testes and induces spermatogenesis. Girls have significantly higher FSH in comparison to the boys at age 5, 10 and 12 years. Luteinizing hormone ( LH or ICSH) LH is glycoprotein, is necessary for proper maturation and function of gonads in both men and women. Both LH and FSH are required for spermatogenesis. All the effect of LH are mediated by way of testosterone. Testosterone and FSH are hormones which are directly on the seminiferous tubular epithelium. FSH and LH are present in the plasma of both males and females at all ages. FSH and LH, in ovulating females, rise sharply from the basal level just prior to ovulation and then rapidly fall. Prolactin In females, prolactin hormone stimulates milk production and is required for establishing a functional corpus luteum in some species. Hyperprolactinemia. There are many causes of Hyperprolactinemia including pregnancy, lactation, pituitary tumors, renal failure and the use of drugs that have dopamine agonist effects. Prolactin synergizes with LH and testosterone to increase the reproductive functions in males. In case of pituitary tumor, all men with small amount of prolactin are impotent regardless of their plasma testosterone levels. Hormones of the middle lobe of the pituitary gland The middle lobe of pituitary gland secretes MSH (melanocytes stimulating hormone). Also known as intermedin. 2 forms of MSH are found α–MSH and β–MSH. α–MSH is a single chain (13 amino acids). β–MSH is polypeptide (22 amino acids). MSH secretion is inhibited by corticosteroids and its activity is inhibited by catecholamines . Actions of MSH Both α–MSH and β–MSH increase melanin biosynthesis by stimulating melanocytes present in dermis and epidermis of the skin. MSH promotes the dispersion of the melanin pigment in entire cells making them dark in appearance. 30-60 mg cortisone is given orally to prevent excess deposition of melanin in skin. Increase in pigmentation is seen in Addison's disease, some cases of thyrotoxicosis and pregnancy . Posterior pituitary hormones Posterior lobe of pituitary gland secretes 2 important hormones: 1) Vasopressin (Pitressin , Antidiuretic hormone, ADH). 2) Oxytocin (Pitocin) Vasopressin It is a cyclic octapeptide Factors that stimulate vasopressin secretion: 1) 2) 3) 4) 5) 6) 7) 8) Pain. Emotional state. Haemorrhage. Dehydration. Salt intake. Acetylcholine. Anaesthetic drugs. Morphine, nicotine and barbiturates. Factors that inhibit vasopressin secretion: 1) Epinephrine. 2) Caffeine. Vasopressin(ADH) functions 1) Regulation of water balance by promoting reabsorption of water in the cells of distal tubules. 2) Its powerful action is raising blood pressure. Failure of hypothalamus to produce enough ADH or preventing of release by damage of the nerve tracts causes an important disorder known as diabetes insipidus, in which volume of urine increases to as much as 20 liters per day. Therefore, the specific gravity of urine decreases to very low (1.001). Normal secretion and release of ADH are regulated by osmoreceptors in the diencephalon of brain. Oxytocin (pitocin) Greek word, oxytocin= rapid birth. Oxytocin is also octapeptide. Oxytocin is powerful stimulant of uterine contraction. The pregnant uterus is more susceptible. Oxytocin appears to be natural initiator of labour. It also facilitates upward movement of spermatozoa in vagina and the fallopian tubes. It also stimulates the contraction of myoepithelial tissue around the ducts of the lactating mammary, thereby, stimulate the ejection of milk (milk letdown action)