Question

Describe hormonal control in various phases of the menstrual cycle.

Describe menstrual cycle in human female.

Answer 1

1. Menstrual phase: Day 1^st - 5^th day.
   The endometrium of the uterus breaks down under the effect of prostaglandins released due to decreased levels of progesterone and estrogen.
2. Proliferative phase/Follicular phase/Post menstrual phase: Day 6^th - 13^th day.
   A few secondary follicles proceed to develop but usually one of them develops into a Graafian follicle (mature follicle). The other secondary follicles degenerate. This process of degeneration is called atresia.
   Developing secondary follicles secrete the hormone estrogen. The stimulation for the proliferation of new follicles is influenced by GnRH which stimulates the release of FSH.
3. Ovulatory phase: It is the shortest phase of the menstrual cycle. It involves rupturing of the mature Graafian follicle and the release of an ovum (secondary oocyte) into the pelvic cavity; usually on the 14^th day of the menstrual cycle. Rapid secretion of LH by a positive feedback mechanism causes the mature follicle to rupture.
4. Secretory phase/Luteal phase: Day 15^th to 28^th day.
   After the release of the secondary oocyte, the remaining tissue of the Graafian follicle transforms into corpus luteum under the effect of LH. The Corpus luteum begins to secrete progesterone and estrogens. The ovulated egg may get fertilized within 24 hours. However, in the absence of fertilization, the corpus luteum can survive for only two weeks and then degenerate into a white scar called corpus Albicans.
   The corpus luteum releases progesterone, a small amount of estrogens and inhibin. Under the influence of these hormones, the endometrial glands grow, become coiled and start uterine secretions. The endometrium becomes more vascularized and thickens up to 8-10 mm. Inhibin stops the secretion of FSH.