Question

Pepsin is a protein digesting enzyme. How is the stomach lining protected against its actions?

Answer 1

The entire alimentary canal and stomach has a lining of mucus. This lining prevents the stomach against the actions of hydrochloric acid and and other digestive enzymes like pepsin.
The stomach is protected by the epithelial cells, which produce and secrete a bicarbonate-rich solution that coats the mucosa. Bicarbonate is alkaline, a base, and neutralizes the acid secreted by the stomach, producing water in the process. This continuous supply of bicarbonate is the main way that stomach protects itself from autodigestion (the stomach digesting itself) and the overall acidic environment.