If there is no fertilization of the ovum, it lives for about a day because each ovary releases a new egg. Therefore, the uterus also prepares every month to receive the fertilized egg. Its end wall becomes fleshy and conjoined. It is necessary for the nutrition of the egg at the time of fertilization. But in the absence of fertilization, even this layer is not needed. Therefore, this layer gradually breaks down and is expelled from the vaginal tract in the form of blood and mucus. This cycle takes about 1 month and it is called the menstrual cycle. Its duration is about 2 to 8 days.