r; 



lancroaiic juice 



Fig. 17-8. The hormonal control of the secretion of pancreatic juice. The acidic food causes prosecretin (black 

 spheres) in the duodenal lining to be converted to secretin (black spheres with a notch) which circulates in the 

 blood, eventually reaching the pancreas where it stimulates the flow of pancreatic juice. 



the small intestine, a fact contrary to ear- 

 lier beliefs. 



The pancreatic juice contains a starch- 

 splitting enzyme (amylase), amylopsin, a 

 protein-splitting enzyme ( proteinase or pro- 

 tease), trypsin (secreted as inactive tryp- 

 sinogen), and a fat-splitting enzyme (li- 

 pase), steapsin. It should be noted that the 

 only true lipase in the entire tract is steap- 

 sin; hence, if this fails there is no chance 

 for fat digestion. The other two enzymes 

 are approximately duplicated in the secre- 

 tions of the mouth and stomach, so that in 

 a depancreatized animal protein and car- 

 bohydrate digestion progresses at a fair rate 

 while fat digestion fails altogether. 



Control of pancreatic juice and bile flow 



The pyloric sphincter relaxes when the 

 content of the stomach reaches a certain 

 consistency, though precisely how this is 

 controlled is not well understood. Once the 

 chyme reaches the duodenum, however, 

 the control of the bile and pancreatic juice 

 flow is rather well known. The wall of the 

 duodenum contains a substance called pro- 

 secretin which, when brought into contact 

 with hydrochloric acid, is converted to a 

 hormone called secretin. Some of this gets 

 into the blood stream where it circulates to 

 the pancreas, causing it to deliver pancreatic 

 juice ( Fig. 17-8 ) . The proof of the action of 



