Respiratory system: absorption atelectasis: 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: absorption atelectasis

Sample item

A post-operative patient is given 100 percent oxygen for many hours. A segmental bronchus is partly obstructed by secretions, and the lung volume of that segment gradually falls. Why does breathing pure oxygen predispose to this?

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

The answer and the reasoning

C. Oxygen is absorbed into the blood faster than it is replaced, and no nitrogen remains to splint the alveoli open

In an alveolus supplied by a narrowed airway, oxygen leaves into the blood faster than inspired gas replaces it. When the inspired gas is mostly nitrogen, this poorly absorbed gas stays behind and keeps the alveolus open; with pure oxygen the gas is fully absorbed and the unit collapses.

Option by option

  • A. Pure oxygen causes bronchospasm of the obstructed segment

    Bronchospasm is not the mechanism of absorption atelectasis.

  • B. High oxygen tension inhibits ciliary beating and stops all gas flow

    Reduced ciliary function does not abolish gas flow and is not the principal mechanism.

  • C. Oxygen is absorbed into the blood faster than it is replaced, and no nitrogen remains to splint the alveoli open (correct)

    Correct. Without a poorly absorbed nitrogen splint, the alveolar gas is absorbed and the unit collapses.

  • D. Pure oxygen destroys surfactant in all alveoli at once

    Oxygen does not destroy surfactant across all alveoli immediately, and the problem is local to a narrowed airway.

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 C, Oxygen is absorbed into the blood faster than it is replaced, and no nitrogen remains to splint the alveoli open. In an alveolus supplied by a narrowed airway, oxygen leaves into the blood faster than inspired gas replaces it.

Why is "Pure oxygen causes bronchospasm of the obstructed segment" not the answer?

Bronchospasm is not the mechanism of absorption atelectasis.

Why is "High oxygen tension inhibits ciliary beating and stops all gas flow" not the answer?

Reduced ciliary function does not abolish gas flow and is not the principal mechanism.

Why is "Pure oxygen destroys surfactant in all alveoli at once" not the answer?

Oxygen does not destroy surfactant across all alveoli immediately, and the problem is local to a narrowed airway.

What concept does this question test?

It tests Respiratory system: absorption atelectasis in Physiology. When the inspired gas is mostly nitrogen, this poorly absorbed gas stays behind and keeps the alveolus open; with pure oxygen the gas is fully absorbed and the unit collapses.

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: absorption atelectasis?

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.