What strong mineral acid is secreted by parietal cells in the gastric lining, maintaining a stomach lumen pH of 1.5 to 2.0 to kill ingested pathogens and activate pepsinogen?
Answer and explanation
Correct answer: D. Hydrochloric acid (HCl)
- Step 1: Parietal (oxyntic) cells in the fundus and body of the stomach use proton pumps (H+/K+ ATPase) to actively secrete hydrogen ions alongside chloride ions.
- Step 2: This produces concentrated hydrochloric acid (HCl), which denatures dietary proteins, destroys harmful swallowed bacteria, and converts inactive pepsinogen into the active proteolytic enzyme pepsin.
Answer
Hydrochloric acid (HCl)
Why not the others: 'Sulfuric acid (H2SO4)' Sulfuric acid is a corrosive industrial chemical not synthesized by biological tissues; 'Nitric acid (HNO3)' Nitric acid is a potent oxidizing agent not found in gastric secretions; 'Acetic acid (CH3COOH)' Acetic acid is the organic acid found in vinegar, not the strong mineral acid in gastric juice.
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