Respiratory system: ventilatory response to metabolic acidosis: 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 · Respiratory system: ventilatory response to metabolic acidosis

Sample item

A patient with severe diabetic ketoacidosis breathes deeply and rapidly with a PaCO2 of 20 mmHg. Which receptors provide the primary stimulus for this hyperventilation?

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

The answer and the reasoning

A. Carotid body chemoreceptors sensing raised plasma hydrogen ion

In metabolic acidosis the plasma hydrogen ion rises, but H+ crosses the blood-brain barrier poorly, so the early drive comes from the peripheral (carotid body) chemoreceptors. The resulting hypocapnia lowers CSF PCO2 and tends to restrain the central drive. Kussmaul breathing is the deep, rapid pattern of this response.

Option by option

  • A. Carotid body chemoreceptors sensing raised plasma hydrogen ion (correct)

    Correct. Peripheral chemoreceptors respond to the rise in plasma H+.

  • B. Aortic arch baroreceptors sensing low blood pressure

    Baroreceptors regulate blood pressure and do not drive the respiratory compensation.

  • C. Pulmonary stretch receptors in the bronchial smooth muscle

    Stretch receptors mediate the inflation reflex and are not the stimulus for this response.

  • D. Central chemoreceptors sensing hydrogen ion that crosses the blood-brain barrier

    H+ ions cross the blood-brain barrier poorly, and the central receptors respond to CO2, which is low here.

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, Carotid body chemoreceptors sensing raised plasma hydrogen ion. In metabolic acidosis the plasma hydrogen ion rises, but H+ crosses the blood-brain barrier poorly, so the early drive comes from the peripheral (carotid body) chemoreceptors.

Why is "Aortic arch baroreceptors sensing low blood pressure" not the answer?

Baroreceptors regulate blood pressure and do not drive the respiratory compensation.

Why is "Pulmonary stretch receptors in the bronchial smooth muscle" not the answer?

Stretch receptors mediate the inflation reflex and are not the stimulus for this response.

Why is "Central chemoreceptors sensing hydrogen ion that crosses the blood-br…" not the answer?

H+ ions cross the blood-brain barrier poorly, and the central receptors respond to CO2, which is low here.

What concept does this question test?

It tests Respiratory system: ventilatory response to metabolic acidosis in Physiology. The resulting hypocapnia lowers CSF PCO2 and tends to restrain the central drive. Kussmaul breathing is the deep, rapid pattern of this response.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Respiratory system: ventilatory response to metabolic acidosis?

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.