Q.(a) Explain the various phases of the menstrual cycle. OR

(a) The menstrual cycle consists of the menstrual, follicular, ovulatory and luteal phases, driven by FSH, LH, estrogen and progesterone. (b) Infertility is the failure to conceive despite regular unprotected intercourse, arising from a range of physical, hormonal, infective or gamete-related causes in either partner.

(a) The human menstrual cycle repeats roughly every 28 days and is controlled by the hypothalamic-pituitary-ovarian hormonal axis. It begins with the menstrual phase (about days 1-5), during which the thickened, vascularised inner lining of the uterus (endometrium), which had built up in the previous cycle in anticipation of a possible pregnancy, breaks down and is shed as menstrual bleeding because the corpus luteum of the previous cycle has degenerated and progesterone/estrogen levels have fallen. This is followed by the follicular (proliferative) phase (about days 5-13), in which Follicle-Stimulating Hormone (FSH) from the anterior pituitary stimulates the growth of several ovarian follicles, one of which matures into a Graafian follicle; the growing follicle secretes rising levels of estrogen, which causes the endometrium to regenerate, thicken and proliferate. Around day 14, a sharp mid-cycle surge in Luteinising Hormone (LH), triggered by the peak in estrogen, causes ovulation - the rupture of the Graafian follicle and release of the secondary oocyte from the ovary. This is followed by the luteal (secretory) phase (about days 15-28), in which the ruptured follicle transforms into the corpus luteum, which secretes large amounts of progesterone (with some estrogen); progesterone converts the endometrium into a secretory, glandular, blood-rich tissue suited for implantation of an embryo. If fertilisation and implantation do not occur, the corpus luteum degenerates (becoming the corpus albicans) around day 26, progesterone and estrogen levels fall sharply, and this hormone withdrawal triggers the next menstrual phase, restarting the cycle.

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