Gastrointestinal: alkaline tide: 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 · Gastrointestinal: alkaline tide

Sample item

After a large meal, venous blood draining the stomach is more alkaline than arterial blood. What is the mechanism?

AGastric mucus releases ammonia into the bloodBChloride shifts into the red cells in gastric veinsCBicarbonate is added to the blood as parietal cells secrete hydrogen ionDLoss of carbon dioxide across the gastric mucosa

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

The answer and the reasoning

C. Bicarbonate is added to the blood as parietal cells secrete hydrogen ion

In the parietal cell, carbonic anhydrase generates H+ and HCO3- from CO2 and water. The H+ is pumped into the lumen by the H+/K+ ATPase while the bicarbonate leaves across the basolateral membrane in exchange for chloride. The bicarbonate raises the pH of gastric venous blood, a change known as the alkaline tide.

Option by option

A. Gastric mucus releases ammonia into the blood
Gastric mucus is not a source of ammonia delivered to the blood in this way.
B. Chloride shifts into the red cells in gastric veins
A chloride shift occurs in red cells in tissue capillaries and does not account for the alkaline tide.
C. Bicarbonate is added to the blood as parietal cells secrete hydrogen ion (correct)
Correct. Each H+ secreted adds one bicarbonate to the blood.
D. Loss of carbon dioxide across the gastric mucosa
Loss of CO2 across the mucosa is not the mechanism.

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 C, Bicarbonate is added to the blood as parietal cells secrete hydrogen ion. In the parietal cell, carbonic anhydrase generates H+ and HCO3- from CO2 and water.

Why is "Gastric mucus releases ammonia into the blood" not the answer?

Gastric mucus is not a source of ammonia delivered to the blood in this way.

Why is "Chloride shifts into the red cells in gastric veins" not the answer?

A chloride shift occurs in red cells in tissue capillaries and does not account for the alkaline tide.

Why is "Loss of carbon dioxide across the gastric mucosa" not the answer?

Loss of CO2 across the mucosa is not the mechanism.

What concept does this question test?

It tests Gastrointestinal: alkaline tide in Physiology. The H+ is pumped into the lumen by the H+/K+ ATPase while the bicarbonate leaves across the basolateral membrane in exchange for chloride. The bicarbonate raises the pH of gastric venous blood, a change known as the alkaline tide.

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 Gastrointestinal: alkaline tide?

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.