A discharged ovum occurs when there is a release of the luteinizing hormone from the hypothalamus. The ovum is released from one of the ovarian follicles for possible fertilization. The escape is known as ovulation. The remains of the follicle stay in the ovary, secreting estrogen and a second hormone, progesterone, which prepares the uterine lining (the endometrium) to receive and nourish a fertilized egg. If the egg is not fertilized, levels of estrogen and progesterone drop and the uterus lining breaks down. It is then shed from the vagina together with mucus and the unfertilized ovum. The resulting bleeding constitutes menstruation.