What role does pituitary gonadotropins play during follicular and ovulatory phases of menstrual cycle? Explain the shifts in steroidal secretions.
NEETprep Answer: Menstrual Phase (1-5 days)
Encromctrium breaks down the cell of endometrium secretions unfertilisecd ovum constitute menstrual flow. Progesteron production is reduced
Follicular Phase (6-13 cays) Encometrium rebuilds, FSH and oestrogen secretion is increased.
Ovulatory Phese (14-16 days) Both LH and FSH attain peak level. Estrogen level is also high. it leacls to ovulation.
Luteal Phase (16-28 days) . In absence of fertilisation corpus luteum secretes pragesterone. Endometrium Thickens and uterine glands become secretary. The menstrual cycle starts with the menstrual phase, when menstrual flow occurs and it lasts for 3-5 days. It results due to breakdown of encometrial lining of the uterus and its blood vessels.
Follicular Phase The menstrual phase is followed by the follicular phase.
During this phase, the primary follicles in the ovary grow to become a fully mature Graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These changes in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones. This causes clisintegration of the endometriurn leading lo menstruation, as well as secretion of estrogens by the growing follicles. Both LH and FSH attain a peak level in the middle of cycle (about t4th day).
Rapid secretion of LH leading to its maximum level during the mid-cycle called LH surge induces rupture of Graafian follicle and thereby the release of ovum (ovulation). The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of the Graafian follicle transform as the corpus luteum. The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium .
Such an endometrium is necessary for implantation of the fertilisecl ovum and other events of pregnancy. In the absence of fertilisation, the corpus luteum degenerates.
This causes clisintegration of the endometriurn leading lo menstruation,
