Reproduction: respiratory changes in pregnancy: 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: respiratory changes in pregnancy

Sample item

A healthy woman at 30 weeks of gestation has arterial pH 7.44, PaCO2 30 mmHg and bicarbonate 20 mmol/L. Which hormone chiefly drives this normal change?

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

The answer and the reasoning

A. Progesterone acting on the respiratory centre

Progesterone increases ventilatory sensitivity to carbon dioxide and raises minute ventilation, giving a compensated respiratory alkalosis with a lowered bicarbonate. This also helps fetal CO2 to cross to the mother.

Option by option

  • A. Progesterone acting on the respiratory centre (correct)

    Correct. Progesterone stimulates ventilation, lowering maternal PaCO2.

  • B. Human placental lactogen acting on the lung

    Placental lactogen acts mainly on metabolism and mammary tissue, not on ventilation.

  • C. Oestriol acting on the carotid body

    Oestriol is a weak oestrogen and is not the principal driver of hyperventilation.

  • D. Relaxin acting on the diaphragm

    Relaxin acts on ligaments and does not change ventilatory drive.

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.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is A, Progesterone acting on the respiratory centre. Progesterone increases ventilatory sensitivity to carbon dioxide and raises minute ventilation, giving a compensated respiratory alkalosis with a lowered bicarbonate.

Why is "Human placental lactogen acting on the lung" not the answer?

Placental lactogen acts mainly on metabolism and mammary tissue, not on ventilation.

Why is "Oestriol acting on the carotid body" not the answer?

Oestriol is a weak oestrogen and is not the principal driver of hyperventilation.

Why is "Relaxin acting on the diaphragm" not the answer?

Relaxin acts on ligaments and does not change ventilatory drive.

What concept does this question test?

It tests Reproduction: respiratory changes in pregnancy in Physiology. This also helps fetal CO2 to cross to the mother.

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: respiratory changes in pregnancy?

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.