Merck Manual

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Quick Facts



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Last full review/revision Sep 2019| Content last modified Sep 2019
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Your digestive system breaks food down into separate nutrients that fuel your body.

Your digestive tract (also called the gastrointestinal or GI tract) is the hollow tube that food goes through when you swallow it, digest it, and then pass the waste products as stool.

What is the stomach?

Your stomach is part of your digestive tract. The stomach is a large, hollow organ with strong muscular walls. Food and liquids you swallow come into your stomach from your esophagus.

The cells lining your stomach release:

  • Mucus

  • Stomach acid

  • A digestive enzyme called pepsin

The mucus protects your stomach from stomach acid. Certain medicines (like aspirin) and certain germs can stop the mucus from doing its job and cause a stomach ulcer.

Stomach acid is hydrochloric acid. The acid helps break down food.

The enzyme pepsin breaks down proteins, such as the proteins in meat.

The muscles in your stomach tighten and relax to mix food with the acid and enzymes (stomach juices). The mixing and the stomach juices break food down into a liquid that your body can absorb. The muscles also help pass food out of your stomach into the small intestine.

Locating the Stomach

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