What protects the stomach walls from digesting the stomach’s own enzymes and acid?

• A. Mucin secreted by mucous cells
• B. Pepsin
• C. Bile
• D. Lipase

Answer: (A)

A protective mucus layer is produced by the mucous cells lining the stomach. The mucin in this mucus forms a thick coating that covers the stomach wall, and together with bicarbonate in the mucus, creates a sturdy barrier against the stomach’s own acid and pepsin. This prevents autodigestion and keeps the stomach lining safe. The other substances aren’t protective in this context: pepsin is the digestive enzyme that could harm tissue if not with the mucus barrier; bile is used for fat digestion in the small intestine; lipase also acts in fat digestion later in the digestive tract. So the mucin secreted by mucous cells is the key protector.