2.1.9Reproduction and Inheritance
Roles of Oestrogen and Progesterone in the Menstrual Cycle — Edexcel International GCSE Science Double Award (Modular) - Biology Unit 2 Revision Notes & Topical Questions
5 min read 6 parts Lesson 10 of 28
Part 1 of 5The menstrual cycle in outline
Timing
- Timing The cycle begins at puberty, usually between about 11 and 14 years old,
- and lasts around 28 days on average,
- although it varies between individuals.
Ovulation
- Ovulation Around day 14 a mature egg is released from an ovary and passes along the oviduct towards the uterus.
Menstruation
- Menstruation If the egg is not fertilised, the thickened uterus lining (endometrium) breaks down and leaves through the vagina.
- This lasts about 5 to 7 days and marks the start of a new cycle.
Rebuilding
- Rebuilding After the period, the lining thickens again, ready for a possible embryo to implant.
Part 2 of 5Stages through the cycle
| Days (approx.) | Event | Uterus lining |
|---|---|---|
| 1 to 5/7 | Menstruation | Breaks down and is lost |
| 5 to 14 | Egg matures in the ovary | Repairs and starts to thicken |
| 14 | Ovulation | Thick and well supplied with blood |
| 15 to 28 | Lining maintained if pregnancy occurs; otherwise it begins to fall | Thick, then breaks down at the end |
Part 3 of 5Oestrogen
1Rises early
- Rises early Oestrogen, made by the ovary, increases from the start of the cycle.
2Lining repairs
- Lining repairs It causes the uterus lining to start thickening and the egg to mature.
3Peak before day 14
- Peak before day 14 The peak is just before ovulation, which is when the egg is released.
Part 4 of 5Progesterone
1Low at first
- Low at first Progesterone stays low for the first half of the cycle.
2Rises after ovulation
- Rises after ovulation Once the egg has been released, progesterone levels climb.
3Maintains lining
- Maintains lining It keeps the uterus lining thick and ready for implantation.
4Falls if no pregnancy
- Falls if no pregnancy A fall in progesterone causes the lining to break down, so menstruation begins.
Part 5 of 5Summary of hormone roles
| Hormone | When it is highest | Main effects |
|---|---|---|
| Oestrogen | Just before day 14 | Thickens uterus lining and matures the egg |
| Progesterone | In the second half of the cycle | Maintains thick lining; a fall triggers a period |
Key terms
| Term | Meaning |
|---|---|
| Ovulation | The release of a mature egg from an ovary. |
| Menstruation | The monthly loss of the uterus lining through the vagina. |
| Endometrium | The soft lining of the uterus. |
| Oestrogen | A hormone from the ovary that repairs the lining and matures the egg. |
| Progesterone | A hormone that maintains the uterus lining. |
| Implantation | Attachment of an embryo to the uterus lining. |
Avoid these mistakes
1
Saying that menstruation is the release of the egg. Menstruation is loss of the uterus lining; ovulation is egg release.
2
Swapping the hormonesoestrogen peaks before ovulation, progesterone rises after it.
3
Writing that high progesterone causes the period. It is the fall in progesterone that triggers the lining to break down.
4
Assuming every cycle is exactly 28 days. This is an average only.
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