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Menstruation

 

Menstruation is the periodic vaginal bleeding that gets the uterus ready for pregnancy by shedding the endometrium, or lining of the womb, and allowing a fresh one to grow in its place.

For most women, menstruation is nothing more than a minor discomfort, but it can cause serious and sometimes debilitating problems for others.

These problems are becoming more common in Western industrialised countries where women are putting off childbearing and having smaller families.

Menstruation stops during pregnancy and breastfeeding, so fewer pregnancies means more periods. If you're having more periods, there's more scope for associated problems to become a major issue.

Period-related woes are a common reason for visits to the GP and a significant cause of lost productivity. Most women will live with menstruation for around 40 years of reproductive life. Menopause, the time when periods stop, occurs around the age of 50 but can occur anywhere between 45 and 55.

Most girls get their first period, or menarche, around the age of 12 years, although anything between eight and 16 years is normal. The age of menarche is affected by genetic and environmental factors, and research around the world has shown that girls in Western countries are getting their periods earlier than their grandmothers did because of improved nutrition and health.

The menstrual cycle is usually described as a monthly event but this is only the case for about 12 per cent of women, or one in nine. Most women's cycles last somewhere between 21 and 35 days, with day one being the day that bleeding begins.

Four key hormones control menstruation. They are oestrogen and progesterone, produced by the ovaries, and follicle stimulating hormone (FSH) and luteinising hormone (LH), released by the pituitary gland in the brain.

This is how the cycle works:

  • Halfway through a woman's cycle FSH levels rise, triggering egg-containing follicles in the ovaries to grow and produce oestrogen
  • The oestrogen causes the lining of the uterus to thicken and develop a rich supply of blood in readiness for a fertilised egg
  • The oestrogen also causes the vagina to secrete sugars, which local bacteria convert into lactic acid, helping reduce the risk of infection
  • Mucus from the cervix becomes thinner to allow sperm easy passage
  • As oestrogen levels peak, the pituitary releases a surge of FSH and LH, triggering ovulation, or the release of an egg from one of the follicles in the ovary
  • The ovary now starts producing progesterone, which helps prepare the endometrium to nourish a growing embryo
  • If an embryo implants and begins to grow, the placenta takes over production of oestrogen and progesterone from the ovary, keeping the endometrium in good condition until the baby is born.
  • If there's no embryo, the ovary stops producing oestrogen and progesterone. This causes the endometrium to break down, triggering a period and resetting the cycle

We think of menstrual fluid as blood but it's actually a mixture of tissues and secretions from inside the uterus. It includes water, mucus, blood and glandular tissue.

Most women menstruate for two days to a week and lose between 20 and 80 millilitres of blood.

The wall of the uterus is also a source of stem cells. This allows the endometrium to replenish itself, but researchers in Japan recently announced they'd harvested stem cells from menstrual blood and say they're hopeful these can be coaxed to turn into heart cells to treat failing or damaged hearts.