Menstruation or a period

Every month, one of the ovaries releases an ovum, and the lining of the uterus thickens in order to receive the future zygote.

If the releases ovum is not fertilised, it dies after a few days. It leaves the body through the vagina, with blood from the lining of the uterus.

This is called menstruation, or a period, as it occurs approximately every month.