The endothelial changes during menstrual cycle has been divided into different phases as :

1. Follicular phase. It begins on the fifth day of cycle. It lasts up to fourteenth day. The endometrium becomes normal. The proliferation changes start. The mucosa thickens and the glands get enlarged. The Graafian follicles get mature.

It is caused by oestrogen and is controlled by FSH of pituitary.

On the 15th day ovulation occurs and corpus luteum develops.

2. Luteal phase or progestational phase. It lasts from 15th to 27th day. Mucosal layer thickens, and the glands get enlarged. The luteum grows further and attains maximum size on the 19th day and degenerates on 27th day. It is caused by progesterone. Formation of corpus luteum and secretion of progesterone are controlled by L.H. of anterior pituitary.

3. Ischamic phase. It is on the 28th day in which first discharge of blood takes place. The corpus luteum degenerates. The level of progesterone falls and is controlled by L.H. of pituitary.

4. Menstruation phase. It lasts for 3 to 5 days. Menstruation occurs. Blood, mucus, stripped off endometrium and an unfertilized ovum pass out as discharge. The main cause is the lack of progesterone.

Menstrual Cycle. It involves cyclic changes in the female's reproductive tract culminating in menstruation, that is, flow of cast off uterine and fallopian tube lining along with blood and tissue fluid through the vagina. It consists of 3 phases : Proliferative phase, secretory phase and menstrual phase.

 Menstrual cycle showing hormonal relations : (A) Gonadotropin,
 (B) Ovarian cycle, (C) Ovarian hormones, (D) Uterine cycle.