Question

Explain menstrual cycle in human females.

Answer 1

A menstrual cycle is the reproductive cycle in all primates and begins at puberty (menarche).

In human females, menstruation occurs once in 28 to 29 days. The cycle of events starting from one menstruation till the next one is called the menstrual cycle. These changes are brought about by ovarian and pituitary hormones. Menstrual phase refers to the beginning of menstruation wherein the endometrium along with its rich blood supply is shed (menses). During this phase, the levels of both the ovarian and the pituitary hormones are low. The level of follicle stimulating hormone (FSH) starts to increase during the later stages of this phase.

2) The menstrual phase is followed by the follicular phase wherein the primary follicles mature into the Graffian follicle under the influence of FSH and LH. The developing follicles release oestrogen which causes the regeneration of the endometrium. Since the follicles and the endometrium proliferate during the follicular phase, it is also known as the proliferative phase.

3) At the time of ovulation, the release of gonadotropins (LH and FSH) increases. The LH and FSH are at their peak in the middle of the cycle (14^thday) and cause the rupture of the Graafian follicle to release the ovum (ovulation). The remains of the Graafian follicle get converted into corpus luteum, which secretes progesterone for the maintenance of the endometrium in case of pregnancy.

4) In absence of pregnancy, corpus luteum degenerates which causes disintegration of the endometrium leading to mensuration and marking a new cycle.