Question

If the proteases such as pepsin and trypsin, digest protein, why don't they digest the stomach and small intestine, since the stomach and small intestine are both made from protein?

Answer 1

Hint: Pepsin is a protein degrading or proteolytic enzyme that is found in the digestive system. Pepsin operates on complex food proteins during digestion, breaking them down into peptides and amino acids that are easily absorbed by the gut epithelium. Although trypsin and pepsin are both proteolytic enzymes secreted by the digestive system to digest proteins, they are not the same.

Complete answer:
In the stomach, pepsinogen is released, and HCl in the gastric juice converts it to active pepsin. Both HCl and pepsin have the potential to corrode the stomach lining; however, a thick coating of mucus keeps the stomach membrane coated at all times.

Because stomach juice is secreted on a regular basis during mealtime, skipping a meal increases the risk of stomach wall injury. Ulcers are caused by pepsin's action on the gut wall.
Pancreatic tissue secretes trypsin as inactive trypsinogen. The enterokinase enzyme converts it to active trypsin once it reaches the small intestine.

Trypsin works in an alkaline environment, and the presence of a protective mucus layer on the gut lining prevents it from causing any damage.

The lining of your mouth, stomach, or intestine will not be digested by enzymes. Inhibitors that deactivate proteases are also found in our bodies' cells and the mucus lining the gastrointestinal tract (enzymes that break down proteins).

Chief cells in the stomach lining secrete pepsin in an inactive form called pepsinogen, which is also known as zymogen. The stomach prevents the auto-digestion of protective proteins in the digestive tract lining by doing so.

Note:
Through the common bile duct, trypsinogen enters the small intestine and is transformed to active trypsin. This active trypsin breaks down food protein into peptides and amino acids in conjunction with the other two major digestive proteinases, pepsin and chymotrypsin.