(i) The uterus prepares itself every month to receive a fertilized egg/zygote- The inner uterus lining (endometrium) becomes thick and is supplied with blood to nourish the embryo.
(ii) If the egg is not fertilized, then the uterus lining is not required. Hence, it breaks down and gets released in the form of blood and mucus through the vagina. This process lasts for 2-8 days. This cycle occurs every month and is known as menstruation.
