General physiology: calcium extrusion from myocytes: 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: calcium extrusion from myocytes

Sample item

In a cardiac myocyte, most of the calcium that entered the cytosol during systole is removed across the sarcolemma by a transporter that uses the inward sodium gradient. Which transporter is this?

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

The answer and the reasoning

B. Sodium-calcium exchanger

The sarcolemmal sodium-calcium exchanger is a secondary active antiporter, usually moving three sodium ions in for one calcium out, driven by the sodium gradient set by the Na-K ATPase. Digoxin raises intracellular sodium, reduces this extrusion and increases contractility.

Option by option

  • A. Sodium-hydrogen exchanger

    The sodium-hydrogen exchanger regulates intracellular pH rather than calcium.

  • B. Sodium-calcium exchanger (correct)

    Correct. The exchanger couples calcium extrusion to sodium entry.

  • C. Sodium-potassium-chloride cotransporter

    The NKCC cotransporter moves sodium, potassium and chloride, not calcium.

  • D. Calcium-activated chloride channel

    A chloride channel does not extrude calcium.

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, Sodium-calcium exchanger. The sarcolemmal sodium-calcium exchanger is a secondary active antiporter, usually moving three sodium ions in for one calcium out, driven by the sodium gradient set by the Na-K ATPase.

Why is "Sodium-hydrogen exchanger" not the answer?

The sodium-hydrogen exchanger regulates intracellular pH rather than calcium.

Why is "Sodium-potassium-chloride cotransporter" not the answer?

The NKCC cotransporter moves sodium, potassium and chloride, not calcium.

Why is "Calcium-activated chloride channel" not the answer?

A chloride channel does not extrude calcium.

What concept does this question test?

It tests General physiology: calcium extrusion from myocytes in Physiology. Digoxin raises intracellular sodium, reduces this extrusion and increases contractility.

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: calcium extrusion from myocytes?

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.