Reproduction: fetoplacental unit: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Reproduction: fetoplacental unit

Sample item

In late pregnancy, a very low maternal oestriol level can suggest fetal compromise. Why does oestriol synthesis depend on both fetus and placenta?

AThe placenta alone synthesises it from cholesterolBThe fetal adrenal and liver supply precursors that the placenta convertsCThe maternal ovary supplies the precursorDThe fetal thyroid synthesises it

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. The fetal adrenal and liver supply precursors that the placenta converts

The placenta lacks 17-alpha-hydroxylase, so it takes DHEA-sulfate from the fetal adrenal, which is 16-hydroxylated in the fetal liver, and converts it to oestriol. Fetal adrenal failure or anencephaly therefore lowers oestriol.

Option by option

A. The placenta alone synthesises it from cholesterol
The placenta cannot make oestriol from cholesterol alone.
B. The fetal adrenal and liver supply precursors that the placenta converts (correct)
Correct. Fetal adrenal and liver precursors are aromatised by the placenta.
C. The maternal ovary supplies the precursor
The ovary is not the source in late pregnancy.
D. The fetal thyroid synthesises it
The fetal thyroid does not make steroid hormones.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, The fetal adrenal and liver supply precursors that the placenta converts. The placenta lacks 17-alpha-hydroxylase, so it takes DHEA-sulfate from the fetal adrenal, which is 16-hydroxylated in the fetal liver, and converts it to oestriol.

Why is "The placenta alone synthesises it from cholesterol" not the answer?

The placenta cannot make oestriol from cholesterol alone.

Why is "The maternal ovary supplies the precursor" not the answer?

The ovary is not the source in late pregnancy.

Why is "The fetal thyroid synthesises it" not the answer?

The fetal thyroid does not make steroid hormones.

What concept does this question test?

It tests Reproduction: fetoplacental unit in Physiology. Fetal adrenal failure or anencephaly therefore lowers oestriol.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Reproduction: fetoplacental unit?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.