Renal: loop diuretics and concentration: 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 · Renal: loop diuretics and concentration

Sample item

After several days of high-dose furosemide, a patient's urine osmolality is close to plasma osmolality at about 300 mOsm/kg regardless of hydration. What is the explanation?

AIncreased aquaporin-2 insertion in the collecting ductBBlocked ADH receptors in the collecting ductCBlocked urea transporters in the inner medullary collecting duct onlyDBlocked NaCl transport in the thick ascending limb reduces the medullary gradient and the diluting segment

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

The answer and the reasoning

D. Blocked NaCl transport in the thick ascending limb reduces the medullary gradient and the diluting segment

Thick ascending limb transport of NaCl by NKCC2 generates the corticomedullary gradient and makes the tubular fluid dilute. Loop diuretics inhibit it, so the medulla cannot be made hypertonic and fluid is not diluted, causing isosthenuria. The collecting duct and ADH remain intact.

Option by option

A. Increased aquaporin-2 insertion in the collecting duct
Increased aquaporin insertion would raise urine concentration, not fix it near plasma.
B. Blocked ADH receptors in the collecting duct
Loop diuretics do not block V2 receptors; that is the action of tolvaptan.
C. Blocked urea transporters in the inner medullary collecting duct only
Urea transporter loss would only partly reduce concentration and does not abolish dilution.
D. Blocked NaCl transport in the thick ascending limb reduces the medullary gradient and the diluting segment (correct)
Correct. Loss of the single effect abolishes both concentrating and diluting capacity.

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 D, Blocked NaCl transport in the thick ascending limb reduces the medullary gradient and the diluting segment. Thick ascending limb transport of NaCl by NKCC2 generates the corticomedullary gradient and makes the tubular fluid dilute.

Why is "Increased aquaporin-2 insertion in the collecting duct" not the answer?

Increased aquaporin insertion would raise urine concentration, not fix it near plasma.

Why is "Blocked ADH receptors in the collecting duct" not the answer?

Loop diuretics do not block V2 receptors; that is the action of tolvaptan.

Why is "Blocked urea transporters in the inner medullary collecting duct only" not the answer?

Urea transporter loss would only partly reduce concentration and does not abolish dilution.

What concept does this question test?

It tests Renal: loop diuretics and concentration in Physiology. Loop diuretics inhibit it, so the medulla cannot be made hypertonic and fluid is not diluted, causing isosthenuria. The collecting duct and ADH remain intact.

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 Renal: loop diuretics and concentration?

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.