General physiology: cyclic GMP signalling: 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 · General physiology: cyclic GMP signalling

Sample item

A patient with angina places a nitroglycerin tablet under the tongue and the chest pain eases as veins dilate. The released nitric oxide relaxes smooth muscle mainly by increasing which messenger?

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

The answer and the reasoning

B. cGMP through soluble guanylyl cyclase

Nitric oxide diffuses into smooth muscle and activates soluble guanylyl cyclase. The rise in cGMP activates protein kinase G, lowers cytosolic calcium and dephosphorylates myosin light chain, causing relaxation.

Option by option

  • A. Intracellular calcium through L-type channels

    Raising intracellular calcium would contract the muscle, not relax it.

  • B. cGMP through soluble guanylyl cyclase (correct)

    Correct. NO activates soluble guanylyl cyclase, and cGMP produces relaxation.

  • C. cAMP through adenylyl cyclase

    cAMP is raised by beta-2 agonists and is not the messenger of nitric oxide.

  • D. IP3 through phospholipase C

    IP3 releases calcium and promotes contraction, the opposite of this response.

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 B, cGMP through soluble guanylyl cyclase. Nitric oxide diffuses into smooth muscle and activates soluble guanylyl cyclase.

Why is "Intracellular calcium through L-type channels" not the answer?

Raising intracellular calcium would contract the muscle, not relax it.

Why is "cAMP through adenylyl cyclase" not the answer?

cAMP is raised by beta-2 agonists and is not the messenger of nitric oxide.

Why is "IP3 through phospholipase C" not the answer?

IP3 releases calcium and promotes contraction, the opposite of this response.

What concept does this question test?

It tests General physiology: cyclic GMP signalling in Physiology. The rise in cGMP activates protein kinase G, lowers cytosolic calcium and dephosphorylates myosin light chain, causing relaxation.

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 General physiology: cyclic GMP signalling?

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.