Updated by: Arabinda Naik
Menstruation occurs in humans, apes, and old monkeys. Menstruation is bleeding from the uterus of adult females at intervals of 28 days (about 4 weeks). In human female menstruation is repeated at an interval of 28 days (about 4 weeks) and the cycle of events starting from one menstruation to the next one is called the menstrual cycle. One ovum is released during the middle of each menstrual cycle i.e., on the 14th day. It is regulated by certain hormones which are secreted by the pituitary gland. The hormones which are secreted by the pituitary gland influence the ovaries. Then the ovaries secrete some hormones which affect the wall of the uterus. The end of the cycle is accompanied by the breakdown of the uterine wall, which gets released in the form of blood and mucus through the vagina. This is known as menses. The cycle does not take place during pregnancy, may be suppressed during lactation, and permanently stops at menopause. The menstrual cycle consists of four phases. Menstrual phase, proliferative phase, ovulatory phase, and secretory phase.