The menstrual cycle is a complex process that involves the release of an egg from the ovary, the thickening of the uterine lining, and the shedding of the uterine lining if the egg is not fertilized. Menstruation is the process of shedding the uterine lining, and it typically lasts for 3-7 days.
During menstruation, the levels of the hormone progesterone are low. Progesterone is responsible for maintaining the uterine lining, so when its levels are low, the uterine lining is shed. The low levels of progesterone also make it less likely that an egg will be fertilized.
