Clinical biochemistry: chloride shift: practice question

A Biochemistry 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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Biochemistry · Clinical biochemistry: chloride shift

Sample item

The chloride content of red cells in venous blood is higher than in arterial blood. Which process explains this?

AChloride enters red cells with potassium through the Na-K-2Cl cotransporterBChloride binds to deoxyhaemoglobin at the haem groupCChloride is pumped in by the sodium-potassium ATPaseDBicarbonate leaves the red cell in exchange for chloride through the band 3 anion exchanger

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

The answer and the reasoning

D. Bicarbonate leaves the red cell in exchange for chloride through the band 3 anion exchanger

In the tissues, CO2 enters the red cell and is hydrated by carbonic anhydrase to bicarbonate. Bicarbonate then leaves the cell via the band 3 anion exchanger in exchange for chloride, which keeps the cell electrically neutral. This is the chloride shift or Hamburger phenomenon, reversed in the lungs.

Option by option

A. Chloride enters red cells with potassium through the Na-K-2Cl cotransporter
Red cells do not rely on the Na-K-2Cl cotransporter for this shift.
B. Chloride binds to deoxyhaemoglobin at the haem group
Deoxyhaemoglobin binds protons and CO2, but chloride does not bind at the haem group.
C. Chloride is pumped in by the sodium-potassium ATPase
The sodium-potassium ATPase pumps sodium and potassium, not chloride.
D. Bicarbonate leaves the red cell in exchange for chloride through the band 3 anion exchanger (correct)
Correct. HCO3- out and Cl- in through band 3 keeps the cell electroneutral as CO2 is carried.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Bicarbonate leaves the red cell in exchange for chloride through the band 3 anion exchanger. In the tissues, CO2 enters the red cell and is hydrated by carbonic anhydrase to bicarbonate.

Why is "Chloride enters red cells with potassium through the Na-K-2Cl cotrans…" not the answer?

Red cells do not rely on the Na-K-2Cl cotransporter for this shift.

Why is "Chloride binds to deoxyhaemoglobin at the haem group" not the answer?

Deoxyhaemoglobin binds protons and CO2, but chloride does not bind at the haem group.

Why is "Chloride is pumped in by the sodium-potassium ATPase" not the answer?

The sodium-potassium ATPase pumps sodium and potassium, not chloride.

What concept does this question test?

It tests Clinical biochemistry: chloride shift in Biochemistry. Bicarbonate then leaves the cell via the band 3 anion exchanger in exchange for chloride, which keeps the cell electrically neutral. This is the chloride shift or Hamburger phenomenon, reversed in the lungs.

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 Clinical biochemistry: chloride shift?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.