Question

Describe the effects of FSH, LH, estrogen & progesterone on the initiation & maintenance of a normal human 28-day menstrual (ovarian) cycle in which fertilization does not occur.

Answer 1

A normal menstrual cycle is of 28 days which can be divided into menstrual phase (day 1 to day 5), proliferative phase (day 6 to day 14), ovulation (day 14th), luteal or secretory phase (day 15 to day 28). Menstrual cycle is the cyclic changes that takes place every 28 days in the uterus and ovaries under hormonal control of anterior pituitary gland (FSH and LH) and ovarian hormones (estrogen and progesterone) which prepares the female for pregnancy.

Follicle stimulating hormone (FSH) is secreted by the anterior pituitary gland which stimulates the recruitment and growth of ovarian follicles. The granulosa cells of the developing follicle produce estrogen which proliferates the uterine endometrium during the follicular phase. On day 14th there is luteinizing hormone (LH) surge from the anterior pituitary gland due to the estrogenic surge which causes the release of mature Graafian follicle from the ovary causing ovulation. After ovulation, the mature Graafian follicle gets converted into corpus luteum which secretes the hormone progesterone that increases the thickness of uterine endometrium increasing the development of endometrial glands and spiral arteries within the endometrium preparing it for the implantation of developing embryo. If fertilization does not happen, the estrogen and progesterone level drops which withdraws the hormonal support of the endometrium thereby causing the necrosis and shedding off endometrium during the menstrual phase (day 1 to day 5) of menstrual (ovarian) cycle.