The uterine lining thickens and becomes richly supplied with blood every month even before fertilisation has occurred. Why does this happen, and what triggers its breakdown if the egg is not fertilised?
Generated by claude-sonnet-4-6 · 2026-06-26 01:07 · grounding rag
Model Answer
The uterine lining thickens and becomes richly supplied with blood in preparation to nourish a fertilised egg (embryo) if implantation occurs. This happens every month because the ovary releases one egg every month, and the uterus simultaneously prepares to receive it.
If the egg is not fertilised, it lives for only about one day. The thickened, spongy lining is then no longer needed. As a result, it slowly breaks down and is shed through the vagina as blood and mucus. This monthly cycle is called menstruation and lasts approximately two to eight days.
Source: Chapter 7, Section 7.3.3(c)
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Explanation
- The question has two parts: (i) why the lining thickens before fertilisation, and (ii) what triggers its breakdown. Address both clearly.
- Key terms examiners look for: spongy lining, nourish the embryo, menstruation, blood and mucus, and the approximate duration (2–8 days).
- The lining thickens due to hormonal preparation linked to the monthly ovulation cycle — the uterus "anticipates" a fertilised egg. When no fertilisation occurs, the hormonal support withdraws and the lining is shed.
- Do not over-explain hormones here; the textbook answer focuses on the functional description, which is sufficient for full marks.