The menstrual period, otherwise known as menstruation or menses, is just one part of the menstrual cycle, a 28-day long process continually performed by your body. The menstrual cycle involves the uterus, cervix, ovaries, fallopian tubes and vagina. These are all aspects of your reproductive system because the menstrual cycle is your body’s way of preparing you for pregnancy. Every month, the reproductive system practices for fertilization of your eggs and the development of a fetus. The process is guided by hormones, particularly estrogen, progesterone, follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

Every month, your uterus prepares for an embryo by thickening its lining with tissue and blood. When an egg is released (ovulation) and if it isn’t fertilized, then the uterus will shed this lining. And that is what your period is—simply the shedding of the uterine lining.