Human Reproductive Hormones (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note

Puberty & Hormones

• During puberty, reproductive hormones cause secondary sex characteristics to develop

• The main male reproductive hormone is testosterone which is produced by the testes; testosterone stimulates sperm production

• The main female reproductive hormone is oestrogen which is produced by the ovaries

  • Oestrogen plays an important role in the menstrual cycle which begins at puberty, as well as causing physical changes to occur in the body (such as breast development)

  • During the menstrual cycle, eggs in the ovaries begin to mature and one is released approximately every 28 days in a process called ovulation

Hormones in the Menstrual Cycle (HT Only)

Higher tier only

• The pituitary gland produces FSH which stimulates the development of a follicle in the ovary

• An egg matures inside the follicle and the follicle produces the hormone oestrogen – so FSH stimulates the production of oestrogen

• Oestrogen causes growth and repair of the lining of the uterus wall and inhibits the production of FSH

• When oestrogen rises to a high enough level it stimulates the release of LH from the pituitary gland which causes ovulation (usually around day 14 of the cycle)

• The follicle becomes a corpus luteum and starts producing progesterone

• Progesterone maintains the uterus lining (the thickness of the uterus wall)

• If the egg is not fertilised, the corpus luteum breaks down and progesterone levels drop

• This causes menstruation – commonly known as having a period

• If fertilisation does occur the corpus luteum continues to produce progesterone, preventing the uterus lining from breaking down (breakdown of the lining would prevent a pregnancy)

• Once the placenta has developed, it starts secreting progesterone and continues to do so throughout the pregnancy to maintain the lining

Remember that hormones travel around the body in the bloodstream but only have an effect on a target organ

Hormone level graphs

• You need to be able to extract and interpret data from graphs showing hormone levels during the menstrual cycle:

Changes in the levels of the pituitary hormones FSH and LH in the blood during the menstrual cycle

• FSH (follicle-stimulating hormone) is released by the pituitary gland and causes an egg to start maturing in the ovary

• It also stimulates the ovaries to start releasing oestrogen

• The pituitary gland is stimulated to release luteinising hormone (LH) when oestrogen levels have reached their peak

• LH causes ovulation to occur and also stimulates the ovary to produce progesterone

Changes in the levels of oestrogen and progesterone in the blood during the menstrual cycle

• Oestrogen levels rise from day 1 to peak just before day 14

  • This causes the uterine wall to start thickening and the egg to mature

• The peak in oestrogen occurs just before the egg is released

• Progesterone stays low from day 1 - 14 and starts to rise after ovulation

• The increasing levels cause the uterine lining to thicken further; a fall in progesterone levels causes the uterine lining to break down (menstruation)