7. Uterine (Menstrual Cycle)

The Uterine cycle of menstruation starts from the first day of the menstrual period, which is also the first day of bleeding. It can be divided into three distinct phases. 1. The Menstrual Phase
This phase is also called the 'bleeding phase' or the 'menstrual period'. It usually lasts from the 1st to the 5th day of the cycle. The duration of bleeding can vary from 2 days to 7 days in different women. Usually the flow is less on the first day, increases during the 2nd and the 3rd day and peters off on the 4th and 5th days.
The menstrual discharge or the bleeding during he period consists of dead endometrial cells, blood, vaginal cells, mucous from the cervix and other necrotic tissue.
The main cause for the occurrence of menstruation is the withdrawal of the ovarian hormones - oestrogen and progesterone - due to the degeneration of the corpus luteum in the ovaries at the end of the ovarian cycle.
The lack of hormones causes the endometrium to shrink. The blood vessels of this region become highly coiled on themselves and the blood stagnates in these coils. The endometrial cells get necrosed due to unavailability of blood. The endometrial tissue soon dies off and passes out of the uterus and vagina as menstrual bleeding.

2. The Proliferative Phase
Once the menstrual bleeding stops there is a short duration of about 48 hours when the endometrium rests and repairs itself ('resting phase'). At this time, the endometrium is disorganized and chaotic and only about 1mm thick.
Under the influence of estrogen produced by the growing Graafian follicles in the ovary, the endometrium, mainly the endometrial cells, proliferates and begins to increase in size and thickness. New blood vessels grow from the stumps of the old vessels. The endometrial glands increase in size, though not in number. The stromal cells assume a compact arrangement. At