Explain the Menstrual Phase - Menstrual Cycle

If the ovum is not fertilized, a high level of progesterone in the blood inhibits the activity of pituitary gland and the production of luteinizing hormone is reduced. The decrease in hormone causes degeneration of corpus luteum. Thus progesterone production is decreased. Around 14 days after ovulation, the lining of uterus degenerates and breaks down, menstruation begins. The flow consists of extra secretion of endometrial cells, blood from broken capillaries and the unfertilized ovum. When progesterone levels decreases considerably, another ovarian follicle is stimulated by FSH and the next cycle begins.