Why doesn’t the stomach digest itself?

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With all the potent hydrochloric acid (HCL) and other digestive juices in the stomach, it’s natural to wonder why the stomach doesn’t digest itself. How is the delicate stomach lining protected, while the equally delicate lining of the esophagus can be damaged, causing acidity?

The answer lies in two primary substances: mucus and bicarbonate, both secreted by cells in the stomach's epithelial lining (the top cell layer).

Mucus, mostly water (95 percent) with a small portion of a sugar-protein substance called glycoprotein (5 percent), has a slightly gel-like quality that helps it stick to the epithelial lining. This mucus is a physical buffer against stomach acid and other digestive juices.

Bicarbonate is alkaline and very effective at neutralizing potent acids. Bicarbonate ions are secreted by cells in the stomach lining in response to contact with acid.

Together, the mucus and bicarbonate coat the gastric epithelium, neutralizing any acid they come into contact with. This mucus-bicarbonate barrier is so effective that while the pH in the stomach cavity can be as low as 2 (very acidic), the pH at the stomach’s lining approaches 7, or neutral.