General physiology: sweat gland ion handling: 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: sweat gland ion handling

Sample item

A 3-year-old with recurrent chest infections and greasy stools has very salty-tasting sweat. Which defect in the sweat gland explains the high sweat chloride?

AFailure of the Na-K ATPase in the secretory coilBFailure of chloride channels in the duct to reabsorb NaCl from sweatCOveractive cholinergic stimulation of the sweat glandsDExcess aldosterone-driven secretion of sodium into the sweat

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

The answer and the reasoning

B. Failure of chloride channels in the duct to reabsorb NaCl from sweat

The secretory coil produces an isotonic fluid, and the duct normally reabsorbs NaCl through CFTR to leave dilute sweat. When CFTR is defective, chloride and sodium stay in the sweat, which becomes salty. This is the basis of the sweat chloride test.

Option by option

A. Failure of the Na-K ATPase in the secretory coil
A failure of the pump in the coil would impair sweat formation rather than leave salt unabsorbed.
B. Failure of chloride channels in the duct to reabsorb NaCl from sweat (correct)
Correct. Defective ductal CFTR prevents salt reabsorption from sweat.
C. Overactive cholinergic stimulation of the sweat glands
More cholinergic drive raises volume but does not make sweat saltier.
D. Excess aldosterone-driven secretion of sodium into the sweat
Aldosterone would increase sodium reabsorption in the duct and lower sweat sodium.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, Failure of chloride channels in the duct to reabsorb NaCl from sweat. The secretory coil produces an isotonic fluid, and the duct normally reabsorbs NaCl through CFTR to leave dilute sweat.

Why is "Failure of the Na-K ATPase in the secretory coil" not the answer?

A failure of the pump in the coil would impair sweat formation rather than leave salt unabsorbed.

Why is "Overactive cholinergic stimulation of the sweat glands" not the answer?

More cholinergic drive raises volume but does not make sweat saltier.

Why is "Excess aldosterone-driven secretion of sodium into the sweat" not the answer?

Aldosterone would increase sodium reabsorption in the duct and lower sweat sodium.

What concept does this question test?

It tests General physiology: sweat gland ion handling in Physiology. When CFTR is defective, chloride and sodium stay in the sweat, which becomes salty. This is the basis of the sweat chloride test.

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: sweat gland ion handling?

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.