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Edexcel GCSE Combined Science · 1SC0
Edexcel 1SC0 · Menstrual Cycle and Assisted Reproductive Technology Check the specification (PDF) (opens in a new tab)
The menstrual cycle coordinates changes in the ovaries with changes in the uterus. An egg matures in an ovary, while the lining of the uterus prepares for a possible pregnancy. If an egg is fertilised, the resulting embryo can implant in this lining.
The cycle begins at puberty. A typical cycle lasts about 28 days, but its length and the timing of its stages vary between individuals and between cycles. Day 1 is the first day of menstruation, or a period.
At the start of the cycle, the uterus lining breaks down and is shed through the vagina. This is menstruation, which commonly occupies roughly the first five days in a simplified 28-day model.
The lining then repairs and thickens, while an egg develops in an ovary. Oestrogen, produced by the ovaries, stimulates this growth and repair. The lining is being rebuilt so that it can support an embryo if pregnancy occurs.
Around day 14 in a typical 28-day cycle, a mature egg is released from an ovary. This is ovulation. The egg enters the oviduct, also called the fallopian tube, and travels towards the uterus.
After ovulation, progesterone maintains the thickened uterus lining, keeping it ready for implantation. If pregnancy does not occur, progesterone levels fall and the lining breaks down. Another period begins, marking day 1 of the next cycle. If pregnancy occurs, progesterone remains high and the lining is maintained rather than shed.
Four interacting hormones coordinate these events. FSH and LH are released by the pituitary gland in the brain; oestrogen and progesterone are produced in the ovaries. Like other hormones, they travel in the bloodstream to their target organs.
FSH stands for follicle-stimulating hormone. A follicle is a structure in an ovary containing a developing egg. FSH stimulates a follicle and its egg to mature, and stimulates the follicle to produce oestrogen.
Oestrogen has effects in two places. In the uterus, it repairs and thickens the lining. At the pituitary gland, it inhibits FSH release, reducing further stimulation of follicles once an egg is developing.
As the follicle develops, oestrogen rises. When oestrogen reaches a high level before ovulation, it stimulates the release of LH from the pituitary gland. LH stands for luteinising hormone. A sharp rise in LH triggers the mature follicle to release its egg: ovulation.
This gives a connected sequence: FSH stimulates follicle development and oestrogen production; high oestrogen stimulates LH release; LH triggers ovulation.
After ovulation, the follicle left behind becomes the corpus luteum. This structure produces progesterone, which maintains the uterus lining. Progesterone also inhibits the release of FSH and LH from the pituitary gland, reducing stimulation of further egg maturation and ovulation during this part of the cycle.
If the egg is not fertilised, the corpus luteum breaks down. Progesterone levels fall, so the uterus lining is no longer maintained and menstruation begins. As inhibition of FSH is reduced, follicle development can begin again for the next cycle.
The important distinction is that oestrogen rebuilds the lining before ovulation, while progesterone maintains it afterwards. Menstruation follows the fall in progesterone, rather than being caused by progesterone itself.
Higher tier: hormones link egg development and ovulation to repair, maintenance and shedding of the uterus lining.
On a menstrual-cycle graph, first check the time axis and identify each hormone using the key. Oestrogen rises to a peak before ovulation, followed by a sharp LH peak around ovulation. Progesterone remains low before ovulation and rises afterwards, when the corpus luteum is active.
Use the order of these changes to explain events, not just describe lines. For example, a fall in progesterone near the end of a cycle means the uterus lining will no longer be maintained, leading to menstruation. Exact hormone concentrations and timings depend on the data shown.
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In a typical 28-day cycle:
Cycle length and timings vary.
| Hormone | Production site | Main effects |
|---|---|---|
| FSH | Pituitary gland | Stimulates follicle and egg maturation and oestrogen production |
| Oestrogen | Ovary | Repairs the lining; inhibits FSH; high levels stimulate LH release |
| LH | Pituitary gland | Triggers ovulation |
| Progesterone | Corpus luteum in the ovary | Maintains the lining; inhibits FSH and LH |
Sequence: FSH → follicle develops → oestrogen rises → LH surge → ovulation → corpus luteum produces progesterone.
No fertilisation: corpus luteum breaks down → progesterone falls → menstruation.
Oestrogen peaks before ovulation; LH peaks around ovulation; progesterone rises after ovulation and falls before menstruation.
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Distinguish ovulation, the release of an egg from an ovary, from menstruation, the shedding of the uterus lining.
Use ‘around day 14 in a typical 28-day cycle’, rather than suggesting that every cycle has identical timings.
For hormone-interaction explanations, link each hormone to its production site and effect: FSH stimulates follicle development; LH triggers ovulation.
Explain menstruation as a consequence of falling progesterone levels, not rising progesterone levels.
The detailed interactions of FSH, LH, oestrogen and progesterone are Higher tier content.
Menstrual cycle
A repeating sequence of changes in the ovaries and uterus, involving egg maturation, ovulation and preparation of the uterus lining for pregnancy.
Menstruation
The breakdown and shedding of the uterus lining, which leaves the body through the vagina as a period.
Ovulation
The release of a mature egg from an ovary.
Follicle
A structure in an ovary that contains a developing egg.
FSH
Follicle-stimulating hormone: a hormone released by the pituitary gland that stimulates follicle and egg maturation in an ovary and stimulates oestrogen production.
LH
Luteinising hormone: a hormone released by the pituitary gland that triggers ovulation.
Oestrogen
A hormone produced by the ovaries that repairs and thickens the uterus lining. It also inhibits FSH release and, at high levels before ovulation, stimulates LH release.
Progesterone
A hormone produced by the corpus luteum after ovulation that maintains the uterus lining and inhibits FSH and LH release.
Corpus luteum
The structure formed from the follicle left in an ovary after ovulation; it produces progesterone.
Put your knowledge into practice — try past paper questions for Combined Science
Menstrual cycle
A repeating sequence of changes in the ovaries and uterus, involving egg maturation, ovulation and preparation of the uterus lining for pregnancy.
Menstruation
The breakdown and shedding of the uterus lining, which leaves the body through the vagina as a period.
Ovulation
The release of a mature egg from an ovary.
Follicle
A structure in an ovary that contains a developing egg.
FSH
Follicle-stimulating hormone: a hormone released by the pituitary gland that stimulates follicle and egg maturation in an ovary and stimulates oestrogen production.
LH
Luteinising hormone: a hormone released by the pituitary gland that triggers ovulation.
Oestrogen
A hormone produced by the ovaries that repairs and thickens the uterus lining. It also inhibits FSH release and, at high levels before ovulation, stimulates LH release.
Progesterone
A hormone produced by the corpus luteum after ovulation that maintains the uterus lining and inhibits FSH and LH release.
Corpus luteum
The structure formed from the follicle left in an ovary after ovulation; it produces progesterone.