Digestion of protein starts in the stomach. The stomach releases gastrin in response to food, which stimulates digestive juices including hydrochloric acid and the enzyme pepsinogen. Pepsinogen is converted to the active enzyme pepsin in the stomach, which breaks proteins down into polypeptides. The pancreas then secretes trypsinogen, chymotrypsinogen and other enzymes into the small intestine to further break down polypeptides into dipeptides, tripeptides and amino acids with the help of the intestinal enzyme peptidase.

1. Digestion of Protein Starts in the
Stomach
Food entering the stomach stimulates
the release of gastrin a hormone which
stimulates the secretion of digestive
juices from cells in the lining of the
stomach wall.

2. Oesophagus Gastric juice
Parietal Pepsinogen
cells
HCl Chief cells Hydrochloric
Acid
Pepsinogen Pepsin
Pepsinogen
Proteins Polypeptide
Pyloric
Sphincter
Diagrammatic representation of a stomach.

3. • Peptic cells secrete pepsinogen
Pepsinogen In the presence Pepsin
of stomach acid
is converted to
Pepsin converts Protein in to Polypeptide

4. E
Pancreas Pancreatic
duct T
T Ts Small
C Intestine
C
Cs
T Trypsinogen
E Enterokinase
Ts Trypsin P P
C Chymotrypsinogen
Cs Chymotrypsin Pp
P Protein Pp Polypeptides Simpkins & Williams, 1987

5. • The enzyme peptidase is released from the
small intestine wall.
Peptidase
Converts
Protein
in to
Amino Acids

6. Absorption of Amino Acids in the Small Intestine
S-cool. 2005.
Glucose
Blood Capillary
Lacteal
Amino Acid
Dipeptide
Tripeptide
Fructose
Bile Salts
Active Transport
Simple Diffusion
Facilitated Transport

7. References
• Simpkins & Williams, 1998 Advanced
Human Biology. Italy: Collins Educational.
• http://www.s-cool.co.uk/topic_quicklearn.asp?loc
, 19.04.05.