Respiratory system: central chemoreceptor adaptation in chronic hypercapnia: 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: central chemoreceptor adaptation in chronic hypercapnia

Sample item

A man with long-standing severe chronic obstructive pulmonary disease retains CO2, but his ventilatory response to inhaled CO2 is blunted. Which adaptation contributes?

ALoss of the peripheral chemoreceptorsBRaised CSF bicarbonate restores CSF pH, reducing the hydrogen ion stimulusCGreater carbonic anhydrase activity in plasmaDDestruction of the central chemoreceptors by hypoxia

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

The answer and the reasoning

B. Raised CSF bicarbonate restores CSF pH, reducing the hydrogen ion stimulus

CO2 diffuses into the CSF, but the choroid plexus gradually transports bicarbonate into it, which restores CSF pH to near normal. The central chemoreceptors then see little acidosis for a given PCO2 and the drive to breathe is weaker.

Option by option

A. Loss of the peripheral chemoreceptors
The peripheral chemoreceptors remain functional, and they provide the hypoxic drive.
B. Raised CSF bicarbonate restores CSF pH, reducing the hydrogen ion stimulus (correct)
Correct. CSF buffering by bicarbonate normalises CSF pH and weakens the stimulus.
C. Greater carbonic anhydrase activity in plasma
Carbonic anhydrase activity does not explain the blunted response.
D. Destruction of the central chemoreceptors by hypoxia
The central chemoreceptors are not destroyed in chronic hypercapnia.

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, Raised CSF bicarbonate restores CSF pH, reducing the hydrogen ion stimulus. CO2 diffuses into the CSF, but the choroid plexus gradually transports bicarbonate into it, which restores CSF pH to near normal.

Why is "Loss of the peripheral chemoreceptors" not the answer?

The peripheral chemoreceptors remain functional, and they provide the hypoxic drive.

Why is "Greater carbonic anhydrase activity in plasma" not the answer?

Carbonic anhydrase activity does not explain the blunted response.

Why is "Destruction of the central chemoreceptors by hypoxia" not the answer?

The central chemoreceptors are not destroyed in chronic hypercapnia.

What concept does this question test?

It tests Respiratory system: central chemoreceptor adaptation in chronic hypercapnia in Physiology. The central chemoreceptors then see little acidosis for a given PCO2 and the drive to breathe is weaker.

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 Respiratory system: central chemoreceptor adaptation in chronic hypercapnia?

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.