By the end of this lesson
- Explain the roles of FSH and LH.
- Sequence the hormonal events around ovulation.
- Apply positive and negative feedback to cycle data.
BIG QUESTION
How does feedback between the pituitary and ovary control the menstrual cycle?
FSH, oestrogen, LH and progesterone form a changing feedback network.
FSH develops a follicle
The anterior pituitary releases FSHFollicle-stimulating hormone: released by the anterior pituitary, it makes a follicle (containing an egg) mature in the ovary and promotes oestrogen secretion., which stimulates an ovarian follicle to mature and promotes oestrogen secretion.
As oestrogen rises, it usually inhibits further FSH release, helping limit the number of follicles that fully mature.
High oestrogen triggers the LH surge
Sustained high oestrogen near mid-cycle switches to positive feedback on the pituitary and produces a surge in LHLuteinising hormone: released by the anterior pituitary, its mid-cycle surge triggers ovulation and the formation of the corpus luteum..
The LH surge triggers ovulation and stimulates formation of the corpus luteum.
Progesterone suppresses another ovulation
The corpus luteum secretes progesterone and some oestrogen. These hormones inhibit FSH and LH, reducing the chance of another follicle maturing during the same cycle.
If no pregnancy occurs, corpus-luteum degeneration lowers progesterone and oestrogen, removing inhibition and allowing a new cycle to begin.
Cycle hormone sequence
Feedback changes over the cycle.
| Hormone/event | Main source | Principal effect |
|---|---|---|
| FSH rises | Anterior pituitary. | Follicle develops; oestrogen rises. |
| Moderate oestrogen | Developing follicle. | Lining grows; FSH is inhibited. |
| Sustained high oestrogen | Mature follicle. | Positive feedback produces LH surge. |
| LH surge | Anterior pituitary. | Ovulation and corpus luteum formation. |
| Progesterone | Corpus luteum. | Lining maintained; FSH/LH inhibited. |
Language that earns precision
- FSH
- Pituitary hormone stimulating follicle development and ovarian oestrogen secretion.
- LH
- Pituitary hormone whose surge triggers ovulation and corpus-luteum formation.
- positive feedback
- Response amplifies the original change.
- negative feedback
- Response opposes the original change.
Common misconceptions
Claim: FSH directly causes menstruation.
Correction: It develops a follicle; menstruation follows falling ovarian hormones.
Claim: LH remains at surge concentration for the whole cycle.
Correction: The surge is brief around ovulation.
Claim: Oestrogen always inhibits LH.
Correction: Sustained high oestrogen near mid-cycle stimulates the LH surge.
Match the answer to the command word
FSH → follicle/oestrogen → LH surge → ovulation → progesterone.
State both the changing hormone and the response it causes.
Recall, apply, then justify
Explain how FSH and LH coordinate ovulation.
Hint
Start with FSH and finish with corpus luteum.
Suggested marking points
- FSH stimulates an ovarian follicle to mature.
- The follicle releases increasing oestrogen.
- Sustained high oestrogen stimulates an LH surge.
- The LH surge triggers ovulation.
- LH also promotes formation of the corpus luteum.
Explain how progesterone reduces the chance of a second ovulation in the same cycle.
Hint
Pituitary inhibition and follicle development.
Suggested marking points
- Progesterone exerts negative feedback on the pituitary/hypothalamus.
- FSH and LH secretion are inhibited.
- Another follicle is less likely to mature and ovulate.
Predict how a drug that prevents LH receptors in the ovary working would alter the cycle.
Planning hint
Follow ovulation, corpus luteum and progesterone.
What a strong design includes
- The ovary would respond poorly to the LH surge.
- Ovulation may fail.
- Corpus-luteum formation would be reduced or absent.
- Progesterone secretion would remain low.
- The uterine lining would be less well maintained after the expected ovulation.
- Fertility would fall because an egg is not released normally.
- Feedback patterns of FSH and LH could also be altered.