Question

Describe or draw the endocrine control in the ovary beginning with the primary oocyte and ending with the degeneration of the corpus luteum. Be sure to include the hormones involved.

Answer 1

Endocrine Control of the Female Reproductive Cycle

• Menstrual Phase
  • Under the influence of follicle-stimulating hormone (FSH), many primordial follicles develop into primary follicles and then into the secondary follicles.
  • Menstrual discharge occurs as a result of decreasing levels of progesterone and estrogen. Decrcrease in the level of these hormones releases prostaglandins that constrict the spiral arterioles of the endometrial lining which eventually slough off.
• Preovulatory Phase
  • Secondary follicles begin secreting estrogen and inhibin. A single secondary follicle becomes dominant. Estrogens and inhibin secreted by this follicle decreases the secretion of follicle-stimulating hormone (FSH) that causes the non-dominant follicles to undergo atresia.
  • During its maturation, the mature follicle increases the secretion of estrogen.
  • Estrogen stimulates the repair of endometrium with its cells undergoing mitosis. Endometrial glands begin to reform.
• Ovulatory Phase
  • High levels of estrogens exert a positive feedback on the cells that are responsible for the secretion of luteinizing hormone (LH) and gonadotropin-releasing hormone (GnRH) and cause ovulation.
  • GnRH promotes the release of follicle stimulating hormone and luteinizing hormone by the anterior pituitary.
  • Luteinizing hormone causes the rupture of the mature follicle and the release of secondary oocyte.
• Postovulatory Phase
  • Under the influence of luteinizing hormone, the theca interna cells of the ruptured follicle mix with the granulosa cells and form the corpus luteum cells.
  • Under the influence of luteinizing hormone, the corpus luteum secretes progesterone, estrogen, relaxin and inhibin.
  • If fertilization does not occur, the corpus luteum degenerates and forms corpus albicans.
  • Decline in the levels of progesterone, estrogen and inhibin cause the release of GnRH, FSH and LH due to the loss of negative feedback suppression by ovarian hormones.
  • If fertilization occurs, the corpus luteum persists by the action of human chorionic gonadotropin (hCG) that is produced by the chorion of the embryo.