Menstruation is monthly uterine bleeding for 4-5 days in 28 days cycle during reproductive life of a woman from menarche to menopause. Menses are normal uterine function whereby endometrium prepares itself to receive the fertilized ovum. In the event of fertilization of the ovum on meeting a sperm, conception takes place and there is no monthly bleeding.
Woman gets 13 menses in a year and around 400 menses in her reproductive life. The menstrual cycle of 28 days starts on day of onset of menstruation and ends at day 28 on start of next.
The body structures that are involved in the normal physiology of the menstrual cycle are:
- The hypothalamus
- The pituitary gland
- The ovaries and
- The uterus.
Ovarian follicles (20 in number) are grown in a menstrual cycle in three steps.
- Ovarian Follicles-are grown from primordial follicles. A single graafian follicle matures and becomes dominant by the effect of FSH while other follicles regress.
- Oestradel- is secreted by maturing ovarian follicle in the circulation – stimulates hypothalamus and anterior pituitary to cause surge of LH and FSH hormones in blood on 12th day of menstrual cycle.
- Ovulation- occurs on 14th day of menstrual cycle. Corpus luteum is in the mature graafian follicle following ovulation due to LH effect. Corpus luteum remains mature from 19th to 26th day, then it degenerates on 27th or 28th day if no pregnancy occurs in menstrual cycle.
- Proliferative phase- Oestradiol from ovarian follicles causes proliferative changes in endometrium (7-10 day)
- Secretory phase- Progesterone from Corpus luteum causes secretary changes in endometrium to receive fertilized ovum for embedding.
- Menstrual breeding- Occurs for 4-5 days due to shedding away of endometrial bits and bleeding from endometrial bed. Menstrual phase is caused by withdrawal of oestradiol and progesterone support to endometrium.