Hormones in Human Reproduction (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

Puberty

• 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

Stages of the menstrual cycle 

• During the menstrual cycle, the lining of the uterus builds up and ovulation occurs

• The average menstrual cycle is 28 days long and there are four overall stages:

  1. Menstruation – loss of lining from the uterus, occurs at the start of the cycle if no fertilisation has occurred

  2. The lining starts to thicken

  3. Ovulation occurs around the middle of the cycle (about day 14), the egg travels down the oviduct towards the uterus

  4. The lining is maintained ready to accept a fertilised egg

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Hormonal control of the cycle

• Four hormones control the events that occur during the menstrual cycle:

  • FSH (Follicle Stimulating Hormone):

    • Produced by the pituitary gland

    • Causes an egg to mature inside a follicle in the ovary

  • Oestrogen:

    • Produced by the ovaries

    • Involved in building and maintaining the uterus lining

  • LH (Luteinising Hormone):

    • Produced by the pituitary gland

    • Stimulates the release of the egg (ovulation)

  • Progesterone:

    • Produced in the ovaries (by the empty follicle/corpus luteum)

    • Maintains the uterus lining during the second half of the cycle

Interactions of the hormones in the menstrual cycle

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 oestrogen

• Oestrogen causes the lining of the uterus wall to thicken 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

• LH also results in an empty follicle (the corpus luteum), which then starts producing progesterone

• Progesterone maintains the uterus lining and inhibits production of FSH and LH

• If the egg is not fertilised, the empty follicle breaks down and progesterone levels drop

• As progesterone levels fall, FSH is no longer inhibited, allowing the cycle to restart

• If fertilisation does occur, the empty follicle continues to produce progesterone, preventing the uterus lining from breaking down

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