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Question Video: Explaining Why Pepsin Does Not Digest the Cells of the Stomach Biology

The stomach itself is made up of proteins; why does the pepsin released by the stomach not end up digesting the stomach?

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Video Transcript

The stomach itself is made up of proteins; why does the pepsin released by the stomach not end up digesting the stomach? (A) The stomach is continually churning and moving to prevent the pepsin from interacting with the stomach muscle. (B) The hydrochloric acid released by the stomach deactivates pepsin if it touches the stomach lining. (C) The epithelial cells of the stomach secrete a protective mucus layer. Or (D) the inside of the stomach is lined with villi, which absorb the pepsin.

You may recall that pepsin is a protease, an enzyme which digests proteins into small peptides. Pepsin is secreted by cells lining the walls of our stomach to digest proteins that are ingested in our food.

Because the stomach itself is made up of proteins, as we’re told in the question, we would expect pepsin to digest the stomach as well as its protein contents. So why doesn’t this happen? If we zoom in on a section of the stomach, we can see the epithelial cells which line its inner surface. These epithelial cells secrete mucus which forms a layer that pepsin cannot penetrate. The mucus therefore acts as a barrier to prevent pepsin from coming into contact with the proteins that make up the stomach.

We have therefore determined that the correct answer is (C). Pepsin does not end up digesting the stomach because the epithelial cells of the stomach secrete a protective mucus layer.

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