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Science

Homeostasis and hormones

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Menstrual cycle and controlling fertility - higher

Menstrual cycle

The menstrual cycle in women is a recurring process in which the lining of the uterus is prepared for pregnancy. If pregnancy does not happen, the lining is shed at menstruation.

Several hormones control this cycle:

  • oestrogen, which causes the repair of the uterus wall
  • progesterone, which maintains the uterus wall

Both hormones are secreted by the ovaries. The image below shows how the levels of oestrogen and progesterone change during the menstrual cycle. If a woman becomes pregnant, the level of progesterone remains high.

Day 1 - 4: menstruation, 4 - 14: lining of uterus builds up, 14 - 28: lining maintained, after day 28: lining breaks down. Egg is released at day 14, then progesterone levels overtake oestrogen levels.

Hormone levels during the mentrual cyle

Controlling fertility

Human fertility is controlled by hormones. This means that a knowledge of hormones can be used to decide to increase, or reduce, the chances of fertilisation and pregnancy.

Marvelon

Contraceptive pills

'The pill' is an oral contraceptive that greatly reduces the chances of mature eggs being produced. The pill contains oestrogen, or oestrogen and progesterone. These hormones prevent eggs from maturing in the ovaries.

Some women have difficulty becoming pregnant because they do not produce enough of a hormone called FSH, which is needed for eggs to mature. Fertility drugs contain FSH, which stimulates eggs to mature in the ovary.

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