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.