What is the role of hydrochloric acid in gastric juice?

Question

BlackTom AI · Accepted Answer

First, let's restate the question and the options to set the context for analysis.
Question: What is the role of hydrochloric acid in gastric juice?
Options:
- a. It regulates the release of gastric juice by stimulating the production of gastrin.
- b. It neutralizes the acidity of the chyme entering the stomach.
- c. It activates the enzyme pepsinogen into pepsin.
- d. It provides lubrication and protection for the stomach lining.

Now, evaluate each option
Option a: It regulates the release of gastric juice by stimulating the production of gastrin. This statement partially touches on gastric regulation, but hydrochloric acid’s primary release-modulating effect is through a feedback mechanism involving sensors and gastrin, not a direct description of HCl stimulating gastrin production itself. In other words, HCl participates in feedback that affects gastrin release, but saying it “regulates the release by stimulating gastrin” is an oversimplification and not the textbook core role of HCl itself.

Option b: It neutralizes the acidity of the chyme entering the stomach. This is incorrect because the stomach’s acidity is maintained by gastric acid itself; neutralization of acid occurs later in the small intestine (by bicarbonate). In the stomach, acid is created to aid digestion, not neutralize chyme there.

Option c: It activates the enzyme pepsinogen into pepsin. This is a correct and central role. Pepsinogen is an inactive zymogen released by chief cells; the acidic environment created by HCl lowers the pH and converts pepsinogen to pepsin, the active protease that begins protein digestion. This alignment with physiology makes option c the accurate description of HCl’s role in gastric juice.

Option d: It provides lubrication and protection for the stomach lining. While gastric mucus and bicarbonate provide mucosal protection, hydrochloric acid itself does not provide lubrication. The corrosive nature of HCl is mitigated by mucus and bicarbonate; describing HCl as providing lubrication is thus inaccurate.

Summary of reasoning for each option:
- a is imprecise about HCl’s direct role in stimulating gastrin and the broader regulatory loop, rather than stating a primary function.
- b is factually incorrect regarding where neutralization occurs and the purpose of gastric acid.
- c correctly identifies the key chemical action of HCl: converting pepsinogen to the active enzyme pepsin, enabling protein digestion.
- d misattributes a lubricating/protective function to HCl that is primarily served by mucus and bicarbonate, not the acid itself.

From the above analysis, option c best matches the true role of hydrochloric acid in gastric juice, explaining why pepsinogen is activated to pepsin in the stomach environment.

BIO 181 (001&002) FALL 2025 4D - Self-Check: Human Digestive System: Esophagus and Stomach (LO 4D.1, 4D.2, 4D.3, 4D.4)

What is the role of hydrochloric acid in gastric juice?

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