Why doesn’t stomach acid burn through our stomach?

Mucus, produced by mucous cells in the stomach lining, protects the stomach from acid.

http://www.cosi.org/resources/askCosi/encyclopedia.asp?qid=195&hotWord=anatomy

The stomach's main secretion is hydrochloric acid and pepsinogen. Pepsinogen is an enzyme precursor that is activated by the acid, and becomes pepsin, an enzyme that breaks down other proteins. Since the wall of the stomach is mostly smooth muscle (protein) it would be broken down by the acid and enzymes if it were't protected. Mucus, secreted in great abundance by mucous cells lining the stomach, is the protection we have.

Mucus is mostly up of mucoprotein that is resistant to almost all digestive juices. It lubricates the passage of food through the gastrointestinal tract, protecting the tract from abrasions. It also is capable of neutalizing both acids and bases. In fact, lapses in stomach mucus production will lead to holes in the stomach wall.

More information on the digestive system can found at:


http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/index.html

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