DHEA is the major C-19 sex steroid produced by the zona reticularis of the adrenal cortex that acts as a weak androgen which promotes virilization in women. During fetal life, contributes to development of the male external genitalia, vas deferens, epididymis, seminal vesicles, and prostate.
Insulin is a polypeptide hormone with two chains of amino acids linked by disulfide bridges synthesized in and secreted by the p cells of the islets of Langerhans in response to glucose. Insulin facilitates the entry of glucose into cells by increasing the number of glucose transporters in the cell membranes, increases transport of amino acids and K+ into cells and increases the activity of Na+-K+ ATPase in cell membranes. Insulin also results in stimulation of protein synthesis, lipogenesis and inhibits protein degradation.
Glucagon is a linear polypeptide hormone with 29 amino acids synthesized in the a cells of the islets of Langerhans and secreted into the portal vein in response to fasting, starvation, glucogenic amino acids, CCK, gastrin, cortisol, exercise, infections, stress, beta-adrenergic stimulators, theophylline, or acetylcholine. Secretion is inhibited by glucose, insulin, somatostatin, secretin, free fatty acids, ketones, pheny-toin, alpha-adrenergic stimulators, GABA. It stimulates gluconeogenesis, glycogenolosis, lypolysis, and ketogenesis in the liver.
Glucagon requires glucocorticoids to exert its gluconeogenetic effects during fasting. Large doses of exogenous glucagon exert a positive inotropic effect on the heart.
Polypeptide hormone synthesized in the A cells of the islets of Langerhans that inhibits the secretion of insulin and glucagons. It causes hyperglycemia, slows gastric emptying, decreases gastric acid secretion. Somatostatin inhibits CCK secretion leading to gallstones in patients with somatostatin secreting pancreatic tumors.
Testosterone is secreted by Leydig cells in males, converted to more active form, dihydrotestosterone. It stimulates growth of the penis and scrotum and promotes development of facial, axillary, and pubic hair. It also inhibits GnRH release from the hypothalamus.
Estrogen exerts negative feedback on release of LH and FSH by the pituitary except in mid-cycle when a surge of LH and FSH occur in response to estrogen. It increases the motility of fallopian tubes and stimulates endometrial growth during first half of menstrual cycle, growth and enlargement of breasts, and pigmentation of areolas, and enlargement of the uterus and vagina.
Progesterone exerts negative feedback on release of LH and FSH by the pituitary except in mid-cycle when progesterone surge enhances release of LH and FSH, leading to ovulation. It stimulates development of lobules and alveoli in the breast and causes progestational changes in the endometrium. Progesterone is responsible for cyclic changes in the cervix and vagina. It decreases the excitability of myometrial cells and their sensitivity to oxytocin.
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