Digestion of proteins : Proteins do not get any justice in buccal cavity.

Digestion of proteins in stomach : The food which comes from buccal cavity into stomach is called bolus. As bolus comes into stomach, immediately enteric epithelium secretes a gastrin hormone. It compels gastric glands to release gastric juice. Gastric juice has HCI, propepsin, prorennin and weak gastric lipase.

Functions of HCI:

1. It is germicidal.

2. It makes medium acidic.

3. It converts propepsin into pepsin.

4. It converts prorennin into rennin.

5. It retards the contraction and relaxation of stomach wall.

6. It stops the action of saliva.

Functions of pepsin :

1. Converts proteins to peptones.

2. Digests collagen.

3. Converts calcium paracaseinate to peptones.

Functions of Rennin : Converts casein of milk into paracasein.

Digestion of proteins into duodenum : In duodenum the food is mixed with bile and pancreatic juice.

Pancreatic juice : It contains 3 proenzymes namely.

1. Tripsinogen : It is converted into trypsin by enterokinase. Trypsin once formed itself converts trypsinogen into trypsin. This process is called autocatalysis and trypsin acts as autocatalyst.

2. Chymotrypsinogen : It is converted to chymotrypsin by trypsin.

3. Procarboxypeptidase : It is converted to carboxypeptidase in the presence of trypsin.

Functions of Trypsin and Chymotrypsin :

1. Converts proteins to peptides.

2. Trypsin acts on keratin present in exoskeleton and converts that to peptones.

Functions of carboxy-peptides : It separates amino acids present adjacent to carboxylic acid group in peptides.

The food is called chyle which passes into jejunum-ileum.

Digestion of proteins in jejunum-ileum : As chyle comes into jejunum-ileum, it is mixed with mucus and intestinal juice. The intestinal juice contains following protein digesting enzyme.

Aminopeptidase : It separates amino acids adjacent to amino group.

Dipeptidase converts dipeptides to amino acids.