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Menstruation is the periodic flow of blood from the uterus, occurring about every twenty-eight days. It is a normal function of the mature female. Menstruation commences at puberty (about age twelve) and continues until Menopause (about age forty-five). It is associated with the release of an ovum from the ovary and is controlled by the hormonal activity of the pituitary gland and the ovary.
During the childbearing years, the lining of the uterus undergoes rapid proliferation of cells in preparation for Pregnancy. When the ovum is not fertilised, this tissue and blood is shed. Ideally, the process continues monthly, during each cycle of the moon, until Pregnancy occurs or until ovulation ceases at Menopause. The natural rhythm of the menstrual cycle may be broken or temporarily halted by hormonal imbalance, illness, emotional disturbance or birth control.
Cycles can be regular, irregular, or absent as well as Painful (dysmenorrhoea), and possibly debilitating. Ovulation should take place at the midpoint but often does not (anovulatory), rendering the woman temporarily or chronically, infertile. Over-exertion has also been blamed for the absence of periods (amenorrhoea) in older women. Lack of body fat also makes amenorrhoea a factor in anorexia.
1. Taymor ML, Sturgis SH, Yahia C. The etiological role of chronic Iron deficiency in production of menorrhagia. JAMA 1964;187:323-27.