What is menstruation?

Menstruation - having periods - is part of the female reproductive cycle that starts when girls become sexually mature at the time of puberty. During a menstrual period, a woman bleeds from her uterus (womb) via the vagina. This lasts anything from three to seven days. Each period commences approximately every 28 days if the woman does not become pregnant during a given cycle.


Why do women menstruate?

A woman's internal sex organs consist of two ovaries, the Fallopian tubes, the uterus (womb) and the vagina. The ovaries contain the eggs with which the woman is born and, during each period, a single egg will usually ripen and mature due to the action of hormones circulating in the bloodstream.

Menstruation is a very complicated process involving many different hormones, the woman's sex organs and the brain. The Follicle Stimulating Hormone causes an egg to mature in an ovary and also stimulates the ovaries to release the hormone oestrogen. Oestrogen then stops further FSH being produced (so as to stop another egg from being released), and stimulates the pituitary gland to release Luteinising hormone, which in turn stimulates the ovary to release the egg. When the egg is mature it bursts from the ovary and drifts through the Fallopian tube down into the uterus. The lining of the uterus - the endometrium - has been thickened by the action of progesterone and made ready to receive the fertilised egg.

If the egg is fertilized and the woman becomes pregnant, it will fasten itself onto the endometrium. If the egg is not fertilized, however, resultant hormonal changes cause the endometrium to slip away and menstruation begins. Menstrual discharge is composed of the endometrium itself, together with a little fresh blood caused by the breaking of very fine blood vessels within the endometrium as it detaches itself from the inside of the uterus. The amount of blood lost due to the normal monthly period is usually less than 80ml.


When does menstruation begin?

These days, girls begin to menstruate when they are about 10 to 14 years-old. The average age is approximately 12. Women will continue to menstruate until the age of 45 to 55, when menopause begins. A woman will have approximately 500 periods in her lifetime.