Which of the following would you expect to occur if fertilisation of an oocyte did not occur?

Question

BlackTom AI · Accepted Answer

After ovulation, the corpus luteum forms from the ruptured follicle and secretes progesterone (and some estrogen). If fertilisation does not occur, no embryo-derived hCG is produced to maintain the corpus luteum, so it degenerates (becomes the corpus albicans) about 10–14 days after ovulation.

1) Relevant knowledge points and concepts
- Corpus luteum: temporary endocrine structure producing progesterone and estrogen during the luteal phase.  
- hCG (human chorionic gonadotropin): produced by a developing embryo; it rescues the corpus luteum and prevents its degeneration.  
- Progesterone/estrogen feedback: high luteal progesterone suppresses pituitary FSH and LH; when progesterone falls, FSH/LH rebound initiating a new cycle.  
- Menstruation: triggered by fall of progesterone/estrogen when corpus luteum degenerates.

2) Step-by-step reasoning
- Ovulation occurs → corpus luteum forms → secretes progesterone to maintain endometrium.  
- If fertilisation and implantation occur → embryo secretes hCG → hCG maintains corpus luteum → progesterone stays high → pregnancy support.  
- If no fertilisation → no hCG → corpus luteum is not maintained → it degrades (corpus albicans).  
- Degeneration causes progesterone and estrogen levels to fall → endometrium sheds (menstruation) and pituitary FSH/LH levels rise again for follicular recruitment.

3) Intermediate steps (timeline)
- Day 0: ovulation and corpus luteum formation.  
- Day ~10–14 post-ovulation: without hCG the corpus luteum degenerates.  
- Immediately after degeneration: progesterone/estrogen fall → menstruation begins; FSH/LH rise.

4) Why the correct answer is correct
Because absence of fertilisation means no embryonic hCG signal to sustain the corpus luteum; therefore it naturally degenerates.

5) Why other options are incorrect
a. Corpus luteum continues growing — false without hCG.  
b. LH and FSH levels would drop — incorrect in the longer term; they are suppressed by progesterone during luteal phase but rise after corpus luteum degeneration.  
c. Progesterone levels would remain high — false; they fall when the corpus luteum degrades.  
d. Estrogen levels would remain high — false for the same reason.

Conclusion: Corpus luteum degrades (option e), which matches the provided correct answer.

Which of the following would you expect to occur if fertilisation of an oocyte did not occur?单项选择题

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