Question

Regulation of the menstrual and estrous cycles provides an excellent example of the integration of hormonal action seen in mammals. Briefly discuss the hormonal interactions involved.

Answer 1

• The regulation of menstrual and estrous cycles exemplifies hormonal integration in mammals. The hypothalamus secretes gonadotropin-releasing hormone (GnRH), stimulating the anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• FSH promotes growth of ovarian follicles and estrogen production.
• Rising estrogen repairs and thickens the uterine lining and triggers a surge in LH, which induces ovulation.
• Post-ovulation, LH transforms the ruptured follicle into the corpus luteum, which secretes progesterone and estrogen to maintain the endometrium for potential implantation.
• Progesterone inhibits FSH and LH to prevent new follicle development.
• Without fertilization, the corpus luteum degenerates, progesterone and estrogen levels fall, causing the endometrium to shed (menstruation) and lifting inhibition on FSH to restart the cycle.
• In estrous cycles, similar hormonal interactions occur, with the key difference that the uterine lining is reabsorbed if pregnancy does not ensue, not shed.
• This dynamic interplay ensures coordinated reproduction and uterine preparedness across cycles.