# E1.4 Reading Hormonal Graphs

F.6 · Biology · Reproductive Cycle Revision · Lesson 4

Identify hormone curves and explain their effects on the ovary and uterine lining.

## Figure

Cycle without pregnancy (schematic; separate relative scales). Ovulation day varies.

## Key points

- **FSH (促卵泡激素):** anterior pituitary → follicle development and oestrogen secretion; smaller surge than LH.
- **LH (促黃體激素):** anterior pituitary → brief, large surge → ovulation; ruptured follicle forms a hormone-secreting yellow body.
- **Oestrogen (雌激素):** follicles and yellow body → uterine lining thickens; rises before ovulation.
- **Progesterone (孕酮):** yellow body → rises mainly after ovulation → maintains lining thickness.
- **Early negative feedback:** rising but still low oestrogen inhibits FSH secretion.
- **Positive feedback:** sustained high oestrogen → LH surge → ovulation. LH is the immediate trigger.
- **After ovulation:** high progesterone and oestrogen inhibit FSH and LH by negative feedback.
- **No pregnancy:** yellow body degenerates → both ovarian hormones fall → lining no longer maintained → menstruation.
- **Combined pills:** oestrogen + progestogen suppress FSH/LH → follicle development and ovulation inhibited → no ovum released for fertilization.
- **IVF:** FSH develops several follicles; LH activity promotes final maturation. Collect ova **before ovulation** → fertilize outside body → transfer embryo(s) into uterus.

## Must know

| Graph / treatment cue | Cause → effect |
|---|---|
| Smaller pituitary surge: curve A | FSH → follicles develop and secrete oestrogen |
| Large, brief pituitary surge: curve B | LH → ovulation; ruptured follicle becomes yellow body |
| Ovarian rise before ovulation: curve C | Oestrogen; sustained high level → positive feedback → LH surge |
| Ovarian rise mainly afterwards: curve D | Yellow body secretes progesterone → lining maintained; luteal hormones inhibit FSH/LH |
| C and D fall near the cycle end | Yellow body degenerates → lining no longer maintained → menstruation |
| Combined pills | Oestrogen + progestogen (progesterone-like hormone) → FSH/LH suppressed → ovulation prevented |
| Fertility treatment | FSH: follicles mature; LH: ovulation; progesterone after ovulation: lining maintained |

In data questions, quote the change shown, then explain its cause and consequence. Fertility drugs can increase multiple-birth risk; in IVF, transferring more than one embryo increases this risk.

## Common mistakes

- ✗ Ovulation is always on day 14. ✓ Use the supplied curve and ovarian events; the day varies between cycles.
- ✗ Oestrogen always inhibits FSH and LH. ✓ Lower oestrogen inhibits FSH; sustained high oestrogen gives positive feedback and the LH surge.
- ✗ The oestrogen peak directly releases the ovum. ✓ Oestrogen causes the LH surge; **LH** triggers ovulation.
- ✗ IVF collects ova after ovulation. ✓ Collect before ovulation, then fertilize outside the body and transfer embryo(s).
- ✗ Every contraceptive pill contains both hormones. ✓ Combined pills contain oestrogen and a progestogen; do not apply that composition to every pill.

## Quick check

1. Identify curves A and B in the left panel. Where are these hormones secreted, and what does B trigger?
2. Identify C and D. Which ovarian structure produces most progesterone after ovulation, and what does it do to the lining?
3. Explain the sequence from C's sustained high pre-ovulation level to the surge in B. Name the feedback mechanism.
4. In a cycle without pregnancy, D falls near the end. Give the ovarian cause and the consequence for the uterine lining.
5. Why is FSH used in IVF, when are ova collected, and where does fertilization occur?

## Answers

1. A: FSH; B: LH. Anterior pituitary; LH triggers ovulation.
2. C: oestrogen; D: progesterone. Yellow body; maintains the lining's thickness.
3. Sustained high oestrogen stimulates LH secretion by the pituitary: positive feedback; the LH surge triggers ovulation.
4. Yellow body degenerates → progesterone (and oestrogen) falls → lining no longer maintained → menstruation.
5. Develops several follicles; collect before ovulation; fertilize outside the body.

## Did you know?

The ovaries do not reliably take turns releasing an ovum. The same ovary can ovulate in consecutive cycles.