Why Doesn't The Stomach Digest Itself?

If you were to put a piece of zinc into a cup of gastric acid, the zinc would dissolve. It's therefore not surprising that the stomach's digestive juices can make short work of anything we deliberately feed to it.

But why doesn't the stomach eat itself? In a manner of speaking, it does. The stomach is lined with a dense layer of cells, called epithelial cells, which continually sacrifice themselves in order to protect deeper layers of the stomach wall. Each minute, the surface lining sheds some 500,000 cells, and it completely replaces itself in three days.

This is in much the same manner that ablative heat shields attached to space vehicles are flaked off and carried away during reentry. This also carries away the heat and protects the vulnerable space capsule lying beneath.

The main components of digestive juices are a protein-digesting enzyme called pepsin and hydrochloric acid. The pepsin is relatively harmless, but hydrochloric acid is extremely caustic and can dissolve tissue in hours. If too much is secreted, the regenerative properties of the epithelial cells may be overcome, the wall breached, and an ulcer produced.

In addition, some substances penetrate the epithelial wall better than others. Among these are vinegar, aspirin, orange juice and many forms of detergents such as those used in some toothpastes.

So when you get up in the morning, if you have a glass of orange juice and an aspirin for breakfast, you're only begging for a case of heartburn.