The Menstrual Cycle

The monthly release of an egg from a womens ovaries and the build up and break down of the protective lining in the uterus (womb) is called the menstrual cycle
Four stages
1. Stage 1 - Lining of the uterus breaks down
  1. Stage 2 - Lining of the uterus builds up
    1. Stage 3 - Egg released
      1. Stage 4 - Lining of the uterus maintained for about 14 days until day 28. If no fertilised egg has landed on the uterus wall by day 28 the spongy lining start to break down and the whole cycle starts again
Hormones control different stages
1. FSH (follicle-stimulating hormone)
  1. Causes an egg to mature in one of the ovaries
    1. Stimulates the ovaries to produce oestrogen
  2. Produced by the pituitary gland
2. Oestrogen
  1. Causes pituitary to produce LH
    1. Inhibits the further release of FSH
  2. Produced in the ovaries
3. LH (Luteinising hormone)
  1. Stimulates the release of an egg at around the middle of the menstrual cycle
  2. Produced by the pituitary gland
Controlling Fertility
1. Hormones can be used to reduce fertility
  1. Oestrogen can be used to prevent the release of an egg so it can be used as a method of contraception
    1. This may seem kind of strange (since naturally oestrogen helps stimulate the release of eggs) But if oestrogen is taken every day to keep the level of it permanently high it inhibits the production of FSH and after a while egg development and production stop and stay stopped
  2. Progesterone also reduces fertility e.g. by stimulating the production of thick cervical mucus which prevents any sperm getting through and reaching an egg
  3. The pill is an oral contraceptive. The first version was made in the 1950s and contained high levels of oestrogen and progesterone (combined oral contraceptive pill)
    1. There were concerns about a link between oestrogen in the pill and side effects like blood clots
      1. Pros
        The pills over 99% effective at preventing pregnancy
        Reduces the risk of getting some types of cancer
      2. Cons
        Isnt 100% effective
        It can cause side effects like headaches, nausea, irregular menstrual bleeding and fluid retention
        It doesnt protect against STDs
2. Increase it
  1. Some women have levels of FSH that are too low to cause their eggs to mature. This means that no eggs are released and the women cant get pregnant
  2. The hormones FSH and LH can be injected by these women to stimulate egg release in the ovaries
  3. Pro
    1. Helps a lot of people to get pregnant
  4. Cons
    1. It doesnt always work - some women may have to do it many times which can be expensive
    2. Too many eggs could be stimulated resulting in unexpected multiple pregnancies
3. IVF
  1. Involves collecting eggs from the womans ovaries and fertilising them in a lab using the mans sperm. These are grown into embryos
    1. Once the embryos are tiny balls of cells one or two of them are transferred to the womens uterus to improve the chance of pregnancy
    2. FSH and LH are given before egg collection to stimulate egg production (so more than one egg can be collecting)
    3. Pro
      1. Fertility treatment can give an infertile couple a child
    4. Con
      1. Some people have a strong reaction to the hormone
      2. There have been some reports of an increased risk of cancer due to the hormonal treatment
      3. Multiple births can happen if more than one embryo grows into a baby

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The Menstrual Cycle

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	Created by sian.allison about 10 years ago