How does the stomach protect itself from being digested

your stomach protects itself from digesting by using epithelial cells, and they protect it by making a bicarbonate rich solution to coat the mucosa.

Your stomach protects itself from being digested by its own enzymes, or burnt by the corrosive hydrochloric acid, by secreting sticky, neutralising mucus that clings to the stomach walls. If this layer becomes damaged in any way it can result in painful and unpleasant stomach ulcers.