Menstruation is one part of a woman's cycle when the lining of the uterus (endometrium) is shed. This occurs throughout a woman's reproductive life. With each monthly cycle, the endometrium prepares itself to nourish a fetus. Increased levels of estrogen and progesterone help thicken its walls.
The menstrual cycle refers to natural changes that occur in the female reproductive system each month during the reproductive years. The cycle is necessary for the production of eggs and the preparation of the uterus for pregnancy.
