1. THE MENSTRUAL CYCLE A Menstruation and Menstrual 1 Menstruation is the periodic discharge of blood from the uterus through the vagina. 2 Normally this occurs once in 28 days.This is known as the menstrual cycle. 3 Menstruation starts from puberty.The menstrual cycle stops at about the age of 50 years.The woman is said to have reached menopause . 4 Menopause takes place because the ovaries do not produce any more egg cells or ova. 5 The menstrual cycle is due to changes in the lining of the uterus 6 The menstrual cycle starts with menstruation.It occurs during the first five days of the cycle.