Respiratory system: inhaled nitric oxide in newborn pulmonary hypertension: 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.

Try it

Physiology · Respiratory system: inhaled nitric oxide in newborn pulmonary hypertension

Sample item

A term newborn with persistent pulmonary hypertension is given inhaled nitric oxide, and pulmonary vascular resistance falls without a fall in systemic blood pressure. Why is the effect limited to the lungs?

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

The answer and the reasoning

A. It is rapidly bound and inactivated by haemoglobin once it enters the blood

Nitric oxide diffuses to pulmonary arteriolar smooth muscle, raises cGMP and relaxes the vessels. Haemoglobin binds it avidly, so there is no systemic vasodilatation. It also selectively improves perfusion of ventilated alveoli and so improves ventilation-perfusion matching.

Option by option

  • A. It is rapidly bound and inactivated by haemoglobin once it enters the blood (correct)

    Correct. Haemoglobin scavenges nitric oxide, which confines its action to the pulmonary vessels.

  • B. It acts only on alveolar epithelium and not on vascular smooth muscle

    It diffuses past the epithelium to act on the vascular smooth muscle.

  • C. It is stored in the lung and released slowly

    Inhaled nitric oxide acts immediately and is not stored.

  • D. Only pulmonary vessels contain guanylyl cyclase

    Guanylyl cyclase is present in vascular smooth muscle throughout the body.

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.

More Physiology questions

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is A, It is rapidly bound and inactivated by haemoglobin once it enters the blood. Nitric oxide diffuses to pulmonary arteriolar smooth muscle, raises cGMP and relaxes the vessels.

Why is "It acts only on alveolar epithelium and not on vascular smooth muscle" not the answer?

It diffuses past the epithelium to act on the vascular smooth muscle.

Why is "It is stored in the lung and released slowly" not the answer?

Inhaled nitric oxide acts immediately and is not stored.

Why is "Only pulmonary vessels contain guanylyl cyclase" not the answer?

Guanylyl cyclase is present in vascular smooth muscle throughout the body.

What concept does this question test?

It tests Respiratory system: inhaled nitric oxide in newborn pulmonary hypertension in Physiology. Haemoglobin binds it avidly, so there is no systemic vasodilatation. It also selectively improves perfusion of ventilated alveoli and so improves ventilation-perfusion matching.

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: inhaled nitric oxide in newborn pulmonary hypertension?

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.