134 DIGESTION 



THE SMALL INTESTINE 



The small intestine is the seat of the greater part both 

 of digestion and of absorption. The digestive changes 

 are due to the action of juices derived from three sources, 

 the pancreas, the hver and the intestine itself. 



THE PANCREAS 



The pancreas consists mainly of tubular alveoh, which 

 are the seat of formation of the pancreatic juice. Separat- 

 ing the alveoh are the Islets of Langerhans, small masses 

 of polyhedral cells not drained by any duct and having a 

 more profuse blood supply than the alveoh. The Islets 

 are beheved to be concerned in carbohydrate metabohsm, 

 and to have no connection with the formation of the 

 external secretion. 



The Pancreatic Juice 



This, the most active of all digestive juices, contains 

 several ferments, of which the most important are the 

 following — 



Trypsin. — When the pancreatic secretion is collected 

 from the duct without being allowed to come into contact 

 with the intestinal epithehum, it has practically no action 

 on proteins. But on addition of a small amount of intes- 

 tinal juice it rapidly develops a strong proteolytic activity. 

 From the fact that the degree of activity is independent 

 of the amount of intestinal juice added, the action of the 

 latter is concluded to be due to a ferment, to which the 

 name enterokinase is given. The proteolytic ferment of 

 the pancreas is therefore secreted in an inactive form — 

 trypsinogen, the activated ferment being called trypsin. 

 Trypsinogen on prolonged standing, even when kept 

 sterile, becomes slowly active — the process being hastened 

 by the addition of hme salts. 



Trypsin, which acts only in alkaline solution, being, in 

 fact, killed by acid, continues the gastric digestion of 



