Updated by: Arabinda Naik
In a 28-day menstrual cycle, the menses takes place in cycle days 3-5. If the secondary oocyte is not fertilized, the corpus luteum starts degenerating due to the progesterone level in the blood declines. Production of estrogens is also reduced in this phase. The production of LH (Luteinizing Hormone) from the anterior pituitary lobe is reduced. The withdrawal of LH hormone causes degeneration of the corpus leutum and thus a consequent fall in the progesterone level the thickened endometrial lining breakdowns from the uterine wall and the unfertilized egg along with the ruptured uterine wall of about 50 ml (about 1.69 oz) of blood and some mucus is discharged through the vaginal orifice and is called menstrual flow.