Explanation

In a 28 day menstrual cycle, the menses takes place. For 3-5 days, the production of LH from the anterior lobe of the pituitary gland considerably reduced. The withdrawal of this hormone causes degeneration of the corpus luteum and therefore, progesterone production is reduced. Production of oestrogen also reduced in this phase (menstrual). The endometrium of the uterus breaks down and menstruation begins. The cells of endometrium secretions and the unfertilized ovum constitute the menstrual flow