Menstruation Menstruation is the periodic bleeding from the vagina that occurs every 28 days. The menses or period consists of blood from the endometrial lining of the uterus .
Periods occur regularly after puberty due to the cyclical activity of the ovaries .
Menstruation begins during puberty, between the ages of 9 and 14 and ends at menopause , usually between the ages of 45 and 50. A woman s period consists of dark-coloured blood mixed with the mucous secretion of the cervical canal and the secretion of the vagina . Menstrual blood does not normally clot as it is low in fibrinogen, does not contain prothrombin, and is rich in calcium. The blood lost during menstruation can be 5 to 80 ml. The average loss is 35 ml.