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I/GCSE Biology -  Puberty and Menstruation

Menstrual cycle and hormones

· IGCSE,Biology,menstrual cycle,Hormones,Puberty

Puberty

When children become teens, they experience changes that lead to sexual maturity. In I/GCSE Biology, these are controlled by hormones. During this period, gametes are produced and the bodies of both sexes are changed to allow reproduction to occur. These events are triggered by the follicle stimulating hormone (FSH) and the luteinising hormone (LH), both produced from the pituitary gland.

Male ♂️

  • FSH stimulates sperm production, while LH instructs testes to secrete testosterone
  • Testosterone controls the development of the male secondary sexual characteristics
  • Growth of penis and testes, growth of pubic hair, muscle development, breaking of the voice, increase in body mass…etc.

Female ♀️

  • FSH and LH control the release of oestrogen from the ovaries
  • Oestrogen controls the development of the female secondary sexual characteristics
  • Breast development, growth of pubic hair, beginning of menstruation, development of rounded shape at hips, increase in body mass…etc.

Menstruation 🩸

A function of the menstrual cycle is to control the development of the uterus lining so if the egg (ovum) is fertilised; the lining will be ready to receive it. If the egg isn’t fertilised, the lining of the uterus breaks down and exits the woman’s body as a flow of menstrual blood and cells called a period.

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In I/GCSE Biology, the cycle is continuous, but day 1 is usually referred to as the first day of menstruation.

👇👇👇The steps of the menstrual cycle:

  1. The pituitary gland releases FSH into the bloodstream, stimulating the growth of an ovum in one of the ovaries. The ovum grows inside a ball of cells called a follicle.
  2. As it grows, the ovary begins to release oestrogen into the bloodstream. This causes a decrease in FSH so no more ova will develop, and thickens the lining of the uterus so it’ll be ready for a fertilised ovum.
  3. Eventually, the increasing amounts of oestrogen triggers a release of LH. This causes ovulation – the follicle bursts open at the edge of the ovary and the egg is released. Meanwhile in the ovary, the follicle begins to develop into a ‘yellow body’ (corpus luteum).
  4. The corpus luteum makes progesterone, which completes the development of the uterus lining and prevents the release of FSH and LH, stopping ovulation.
  5. If the egg is not fertilised, the corpus luteum breaks down and stops making progesterone. This causes the uterus to break, and menstruation then occurs. If the egg is fertilised, then sooner or later, the placenta takes over the secretion of progesterone.
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That's the end of the topic!

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Drafted by Joey (Biology)

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