Biology of Androgens and Estrogens Essay Example | Topics and Well Written Essays - 1500 words

Biology of Androgens and Estrogens - Essay Example In the males androgens produced by the testes and adrenal cortex contribute to the male sex hormones circulating in the blood. Adrenal androgens normally have little physiological effect other than a role in development before the start of puberty in both girls and boys. This is because the male sex hormone activity of the adrenal androgens is weak. Androgens regulate male secondary sexual characteristics and can cause virilizing symptoms in women. Normally androgens are secreted mainly from the male testes, but moderate amount is also secreted from the adrenal gland. Normally adrenal androgens have a minimal effect in males whose sexual characteristics are predominately determined by gonadal steroids such as testosterone. On the contrary, in disease states in females, several androgen-like effects, such as, sexual hair, are largely mediated by adrenal androgens. The principal adrenal androgens are DHEA, androstenedione, and 11-hydroxyandrostenedione. DHEA and androstenedione are wea k androgens and exert their effects via conversion to the potent androgen testosterone in extraglandular tissues. DHEA also has poorly understood effects on the immune and cardiovascular systems. Adrenal androgen formation is regulated by ACTH, not by gonadotropins, thus are suppressed by exogenous glucocorticoid administration. The male reproductive system regulates sexual differentiation, virilization, and the hormonal changes that accompany puberty, ultimately leading to spermatogenesis and fertility. Under the control of the pituitary hormones, namely, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), the Leydig cells of the testes produce testosterone and germ cells are nurtured by Sertoli cells to divide, differentiate, and mature into sperm (Holdcraft, RW. and Braun, RE., 2004).. Estrogens Steroidal estrogens arise from androstenedione or testosterone by aromatization of the A ring. The reaction is catalyzed by a cytochrome P450 monooxygenase enzyme complex. The ovaries are the principal source of circulating estrogen in premenopausal women, with estradiol being the main secretory product. Gonadotropins, acting via receptors that couple to the Gs-adenylyl cyclase-cyclic AMP pathway, increase the activities of aromatase. The follicular theca cells, under control of LH, produce androgens that diffuse to the follicular granulosa cells, where they are converted to estrogens via an FSH-supported aromatization reaction. Estrogens are endogenous hormones that produce numerous physiological actions. In women, these include developmental effects, neuroendocrine actions involved in the control of ovulation, the cyclical preparation of the reproductive tract for fertilization and implantation, and major actions on mineral, carbohydrate, protein, and lipid metabolism. Estrogens also have important actions in males, including effects on bone, spermatogenesis, and behavior. In postmenopausal women, the principal source of circulating estrogen is adipose tissue stroma, where estrone is synthesized from dehydroepiandrosterone secreted by the adrenals. In men, estrogens are produced by the testes, but extragonadal production by aromatization of circulating C19 steroids accounts for most circulating estrogens. Thus, the level of estrogens is regulated in part by the availability of androgenic precursors. Estrogenic effects most often have