If the egg is not fertilized, it lives for one day and is then expelled. This sets in motion which is called menstrual or ovarian cycle. The first menstruation is called menarche. It stops between age 45–50 years. Stoppage of menstruction permantely is called menopause. Menstrual cycle consists of four phases.
Menstrual Phase :
It is characterized by menstruation (= menses, GK. mensum-month) or discharge of blood. mucus and endometrial lining. Menstrual phase lasts for 3–5 days.
Proliferative Phase :
There is repair and growth of endometrium. Under the influence of hormone FSH, a few follicles grow but only one follicle called Graafian follicle matures in the two ovaries. It secretes hormone estrogen Proliferative phase lasts from 5th to 14th day.
Ovulation Phase :
At about the middle of the menstrual cycle on 13th or 14th day, the growing follicle bursts and mature ovum is released from the ovary under the influence of estrogen and LH.
Secretory Phase :
It lasts from middle of menstrual phase to end of the same, i.e., 14–28 days. During this period the uterine wall thickness further. Glands present in endometrial area become functional and begin to secrete of materials for nourishment of the egg if it happens to get fertilised.