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Hormones do far more than control glucose and temperature. They also drive the great changes of puberty and run the menstrual cycle, and we can use our knowledge of them both to prevent pregnancy (contraception) and to treat infertility. This lesson covers the hormones of reproduction: testosterone and oestrogen at puberty, the four hormones of the menstrual cycle (FSH, LH, oestrogen and progesterone), how those hormones can be controlled with contraception, and how they can be used to help people who are struggling to conceive. This is part of Topic B3 of OCR Gateway Science A.
By the end of this lesson you should be able to describe the role of hormones at puberty, name the four menstrual-cycle hormones and their roles, (Higher) explain how they interact to control the cycle, compare hormonal and barrier methods of contraception, and evaluate the use of hormones to treat infertility.
During puberty, the body develops the secondary sexual characteristics — the physical changes of becoming an adult capable of reproduction. These changes are triggered by reproductive hormones.
So testosterone is the principal male hormone and oestrogen the principal female hormone, each controlling the changes of puberty in its sex.
Secondary sexual characteristics are the features that develop at puberty (such as body hair, voice changes, breast development and the growth spurt). They are different from the primary sexual characteristics — the reproductive organs themselves, which are present from birth. The job of the puberty hormones is to bring about the secondary characteristics and to make the reproductive system functional — for example, by starting sperm production in males and the menstrual cycle in females. These changes happen gradually over several years, a slow and long-lasting process that suits hormonal rather than nervous control.
Exam Tip: Pair the hormone with its gland and sex: testosterone – testes – male; oestrogen – ovaries – female. A common slip is to write that testosterone is made by the pituitary; it is made by the testes.
The menstrual cycle is a roughly 28-day cycle in females that prepares the body for a possible pregnancy each month. It is controlled by four hormones released by the pituitary gland and the ovaries.
The cycle has key events:
| Hormone | Released by | Main role |
|---|---|---|
| FSH (follicle-stimulating hormone) | Pituitary gland | Causes an egg to mature in the ovary; stimulates the ovaries to release oestrogen |
| Oestrogen | Ovaries | Causes the uterus lining to build up; (Higher) stimulates the release of LH and inhibits FSH |
| LH (luteinising hormone) | Pituitary gland | Triggers ovulation (the release of the egg) at about day 14 |
| Progesterone | Ovaries | Maintains the uterus lining in the second half of the cycle; (Higher) inhibits FSH and LH |
The diagram shows the cycle as a timeline: menstruation first, then the lining building up under oestrogen, then ovulation triggered by LH at about day 14, then the lining maintained by progesterone until day 28.
Higher tier only: The four hormones control each other in a feedback loop that drives the cycle forward:
flowchart TD
A["FSH (pituitary)<br/>matures egg, stimulates oestrogen"] --> B["Oestrogen (ovary)<br/>builds lining, inhibits FSH, stimulates LH"]
B --> C["LH (pituitary)<br/>triggers ovulation (~day 14)"]
C --> D["Progesterone (ovary)<br/>maintains lining, inhibits FSH and LH"]
D -.->|"if no fertilisation, levels fall,<br/>lining breaks down, cycle restarts"| A
Exam Tip (Higher): Keep the two pituitary hormones and the two ovary hormones straight. FSH and LH come from the pituitary; oestrogen and progesterone come from the ovaries. FSH matures the egg; LH triggers ovulation; oestrogen builds the lining; progesterone maintains it.
The whole point of the menstrual cycle is to prepare the uterus for a possible pregnancy. If the released egg is fertilised by a sperm and the resulting embryo implants in the thickened uterus lining, then progesterone levels stay high instead of falling. This keeps the uterus lining in place to support the developing embryo, and the high progesterone also stops further eggs maturing (so menstruation does not happen and the cycle pauses during pregnancy). If the egg is not fertilised, progesterone and oestrogen fall, the lining can no longer be maintained, and it breaks down as menstruation — and the cycle begins again. Understanding this helps explain why progesterone is sometimes called the hormone that "maintains pregnancy", and why hormonal contraceptives based on progesterone are so effective at preventing the cycle from releasing an egg.
Contraception means preventing pregnancy. Methods fall into two broad groups: hormonal methods (which use hormones to stop the cycle producing or releasing eggs) and non-hormonal / barrier methods (which physically stop sperm reaching the egg, or avoid fertilisation in other ways).
Hormonal contraceptives usually contain oestrogen and/or progesterone. These hormones inhibit FSH, so no egg matures and ovulation is prevented; progesterone also thickens the mucus at the entrance to the uterus, making it harder for sperm to get through. Hormonal methods include:
These do not use hormones:
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