Once a girl reaches puberty, the ovaries, in response to hormones released by the brain, start to release ova. An ovum is released from the ovaries into one of the fallopian tubes about every 28 days. This process is called ovulation. The walls of the uterus get thicker with extra blood and tissue in preparation forfertilisation. However, if fertilisation does not happen, the ovum dries up and leaves the body through the vagina about two weeks later. Blood, and the thickened lining of the uterus comes away too, and this is what women experience as menstruation. Menstruation typically lasts from three to five days. Women menstruate until they have no eggs left. This usually happens when a woman is about 50. This period is called the menopause.
