USA Biology Olympiad (USABO) Practice Exam

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Why is pepsinogen secreted as a zymogen into the stomach?

To enhance protein digestion
To prevent digestion of the gastric glands
To regulate stomach acidity
To activate other digestive enzymes

The correct answer is: To prevent digestion of the gastric glands

Pepsinogen is secreted as a zymogen to prevent the premature digestion of the gastric glands themselves. In its inactive form, pepsinogen is not capable of catalyzing the breakdown of proteins. This is crucial because the stomach contains cells and tissues that produce this enzyme and are essential for digestion. If pepsinogen were to be active as pepsin within the gastric glands, it could lead to autodigestion, where the enzyme begins to digest the very cells that produce it. By releasing pepsinogen in an inactive form, the body effectively protects the gastric lining while ensuring that protein digestion can occur once pepsinogen is activated by the acidic environment of the stomach. The activation of pepsinogen to pepsin occurs when it encounters hydrochloric acid, which is secreted by parietal cells in the stomach. This careful regulation allows for efficient protein digestion while safeguarding the integrity of the stomach’s lining.