What is the menstrual cycle ? Describe its phases.

Answer: The cyclic changes that take place in the female reproductive system (ovary and uterus) about every 28 days, from puberty till menopause, are called the menstrual cycle. It is controlled by the hormones FSH and LH of the pituitary gland and oestrogen and progesterone of the ovary.

1. Menstrual phase (about days 1–5): if the ovum of the previous cycle was not fertilised, the thick inner lining (endometrium) of the uterus breaks down and flows out with blood through the vagina. This is menstruation.
2. Proliferative (follicular) phase (about days 6–14): under the effect of FSH a follicle in the ovary grows and secretes oestrogen, which rebuilds the endometrium. Around the 14th day the follicle bursts and releases the ovum (ovulation), due to LH.
3. Secretory (luteal) phase (about days 15–28): the empty follicle becomes the corpus luteum, which secretes progesterone. The endometrium becomes thick, soft and rich in blood vessels, ready to receive an embryo. If fertilisation does not occur, the corpus luteum degenerates, progesterone falls and the next menstruation begins.