General physiology: secondary active transport: 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: secondary active transport

Sample item

A 5-year-old child with cholera has profuse watery diarrhoea. Oral rehydration solution is effective even though the toxin drives secretion, mainly because:

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

The answer and the reasoning

C. Sodium-glucose cotransport at the enterocyte brush border stays intact and pulls in sodium and water

Cholera toxin raises cAMP in crypt cells and opens CFTR chloride channels, causing secretion. The villus enterocyte SGLT1 symporter, which moves one glucose with two Na+ down the Na+ gradient set by the basolateral Na+-K+ ATPase, is not damaged. Water follows the absorbed solute, so glucose-containing solutions rehydrate.

Option by option

  • A. Glucose stimulates the crypt cell Na+-K+-2Cl- cotransporter and so reverses the net secretion

    Secretion arises from cAMP-driven CFTR opening, and glucose does not reverse it through the crypt cotransporter.

  • B. Glucose crosses the brush border by GLUT2, which is not affected by the toxin and carries water along

    GLUT2 is the basolateral exit route; the apical entry route is SGLT1.

  • C. Sodium-glucose cotransport at the enterocyte brush border stays intact and pulls in sodium and water (correct)

    SGLT1 is a secondary active transporter whose function persists, so glucose and sodium absorption drive water uptake.

  • D. Luminal glucose inactivates cholera toxin so that chloride secretion by the crypt cells stops

    Glucose does not inactivate the toxin, which acts through irreversible activation of adenylyl cyclase.

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, Sodium-glucose cotransport at the enterocyte brush border stays intact and pulls in sodium and water. Cholera toxin raises cAMP in crypt cells and opens CFTR chloride channels, causing secretion.

Why is "Glucose stimulates the crypt cell Na+-K+-2Cl- cotransporter and so re…" not the answer?

Secretion arises from cAMP-driven CFTR opening, and glucose does not reverse it through the crypt cotransporter.

Why is "Glucose crosses the brush border by GLUT2, which is not affected by t…" not the answer?

GLUT2 is the basolateral exit route; the apical entry route is SGLT1.

Why is "Luminal glucose inactivates cholera toxin so that chloride secretion…" not the answer?

Glucose does not inactivate the toxin, which acts through irreversible activation of adenylyl cyclase.

What concept does this question test?

It tests General physiology: secondary active transport in Physiology. The villus enterocyte SGLT1 symporter, which moves one glucose with two Na+ down the Na+ gradient set by the basolateral Na+-K+ ATPase, is not damaged. Water follows the absorbed solute, so glucose-containing solutions rehydrate.

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: secondary active transport?

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.