Q.14 Proenzyme pepsinogen is secreted from ‘P’ of gastric mucosa and converted into active enzyme pepsin on exposure to ‘Q’ secreted from ‘R’. Choose the CORRECT combination of P, Q and R.
Correct option is (A) P – chief cells, Q – hydrochloric acid, R – oxyntic cells.
Pepsinogen is secreted by gastric chief (peptic) cells and is converted to pepsin by hydrochloric acid released from parietal/oxyntic cells in the gastric mucosa.
Introduction
Proenzyme pepsinogen is a zymogen released into the stomach lumen where it must be activated to pepsin for effective protein digestion. Understanding which gastric cells secrete pepsinogen and which cells supply the hydrochloric acid that activates it is essential for mastering human physiology and acing MCQs in exams like NEET and CSIR NET.
Step-by-step solution of the MCQ
The question:
“Proenzyme pepsinogen is secreted from ‘P’ of gastric mucosa and converted into active enzyme pepsin on exposure to ‘Q’ secreted from ‘R’. Choose the correct combination of P, Q and R.”
Key physiological facts:
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Gastric chief (peptic/zymogenic) cells secrete the inactive enzyme pepsinogen.
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Hydrochloric acid (HCl) in the gastric lumen converts pepsinogen into active pepsin and provides the optimal low pH.
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Parietal cells, also called oxyntic cells, are the cells that secrete hydrochloric acid.
So:
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P= chief cells (site of pepsinogen secretion)
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Q= hydrochloric acid (agent that converts pepsinogen to pepsin)
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R= oxyntic (parietal) cells (source of HCl)
This matches option (A).
Explanation of each option
Option (A)
P – chief cells; Q – hydrochloric acid; R – oxyntic cells
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Chief (peptic/zymogenic) cells in gastric glands secrete pepsinogen, the inactive precursor of pepsin.
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Hydrochloric acid converts pepsinogen into pepsin and is produced by parietal/oxyntic cells in the fundus and body of the stomach.
This option correctly links the secreting cell (chief cell), the activating agent (HCl) and the HCl‑secreting cell (oxyntic cell), so it is correct.
Option (B)
P – parietal cells; Q – enterokinase; R – chief cells
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Parietal cells mainly secrete hydrochloric acid and intrinsic factor, not pepsinogen, so they cannot be P.
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Enterokinase (enteropeptidase) is an enzyme of the small intestinal mucosa that activates trypsinogen, not pepsinogen, and therefore cannot be Q.
Thus P and Q are both wrong in this combination, so option (B) is incorrect.
Option (C)
P – oxyntic cells; Q – hydrochloric acid; R – parietal cells
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Oxyntic cells and parietal cells are two names for the same HCl‑secreting cell type; neither primarily secretes pepsinogen.
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Assigning oxyntic cells as P (source of pepsinogen) misidentifies the pepsinogen‑secreting cell, so the sequence P–Q–R is physiologically wrong even though Q and R are individually associated with HCl.
Therefore option (C) is incorrect.
Option (D)
P – peptic cells; Q – gastrin; R – oxyntic cells
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Peptic cells is another name for chief cells, so P alone is acceptable as a source of pepsinogen.
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However, Q here is gastrin, a hormone produced by G‑cells in the pyloric region that indirectly stimulates acid secretion; it does not directly convert pepsinogen to pepsin.
Since pepsinogen is activated by hydrochloric acid, not by gastrin, option (D) is incorrect.
Key exam points to remember
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Gastric chief/peptic cells → secrete pepsinogen (inactive).
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Gastric parietal/oxyntic cells → secrete hydrochloric acid and intrinsic factor.
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Hydrochloric acid → converts pepsinogen to pepsin and maintains acidic pH for optimal protease activity.
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G‑cells → secrete gastrin, which stimulates parietal and chief cells but does not itself activate pepsinogen.
Using these relationships, similar MCQs can be solved rapidly by mapping each step: “which cell secretes what, and what activates which zymogen?”
