Reproductive hormones (AQA GCSE Biology): Revision Notes
Reproductive hormones
The menstrual cycle
The menstrual cycle happens in women from puberty until around age 50. It repeats roughly every 28 days. During this cycle, important changes occur in both the ovaries and the uterus.
While the average cycle is 28 days, normal cycles can range from 21 to 35 days. The timing can vary between individuals and even between cycles for the same person.
Key events in the cycle:
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Menstruation - This is when the thick lining of the uterus breaks down and leaves the body. It starts on day 1 and usually lasts about 5 days.
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Ovulation - An egg is released from one of the ovaries. This typically happens around day 14 of the cycle.
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Fertile period - Days 14 to 16 are when a woman is most likely to become pregnant if sperm are present.
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Uterus lining rebuild - After menstruation, the lining of the uterus gradually thickens again, especially during weeks 3 and 4 of the cycle.
If fertilisation doesn't happen, the cycle starts again with menstruation.
Hormones that control the cycle
Four main hormones work together to control the menstrual cycle. These hormones are produced by different organs and have specific roles in coordinating the complex changes that occur during each cycle.
FSH (Follicle-stimulating hormone)
- Makes eggs in the ovaries develop and mature
- Released from the brain
LH (Luteinising hormone)
- Triggers the ovary to release a mature egg (ovulation)
- Also released from the brain
Oestrogen
- Helps maintain and thicken the uterus lining
- Made by the ovaries
- Main female hormone involved in puberty
Progesterone
- Works with oestrogen to keep the uterus lining healthy
- Made by the ovaries after ovulation
The brain hormones (FSH and LH) control the ovary hormones (oestrogen and progesterone), which in turn control changes in the uterus. This creates a coordinated system that repeats every month.
Male reproductive hormone
Testosterone is the main male reproductive hormone. This powerful hormone is responsible for both the development of male characteristics and the ongoing production of sperm throughout a man's adult life.
What testosterone does:
- Controls sperm production in the testes
- Causes puberty changes in boys such as:
- Growth of testes and penis
- Voice breaking (getting deeper)
- Facial hair growth
- General growth spurt
- Development of underarm and pubic hair
Unlike the female cycle, testosterone production is relatively constant in healthy males, maintaining steady levels throughout most of their adult life.
Female puberty changes
Oestrogen is the main hormone responsible for female puberty changes. This hormone transforms girls into women by triggering the development of female characteristics and establishing the reproductive cycle.
Key changes include:
- Breast development
- Start of menstrual cycles
- General growth spurt
- Development of underarm and pubic hair
Both boys and girls experience growth spurts and develop body hair during puberty, but different hormones control these changes.
Key Points to Remember:
- The menstrual cycle lasts about 28 days and repeats from puberty to menopause
- Four hormones control the cycle: FSH, LH, oestrogen, and progesterone
- Ovulation happens around day 14 when an egg is released
- Testosterone controls male development and sperm production
- Oestrogen controls female development and puberty changes