CHAPTER X 

 PANCREATIC DIGESTION 1 



As soon as the food mixture leaves the stomach it comes into inti- 

 mate contact with the bile and the pancreatic juice. Since these fluids 

 are alkaline in reaction (see -Bile, page 205) there can obviously be no 

 further peptic activity after they have become intimately mixed with 

 the chyme and have neutralized the acidity previously imparted to it 

 by the hydrochloric acid of the gastric juice. The pancreatic juice 

 reaches the intestine through the duct of Wirsung which opens into the 

 intestine near the pylorus. 



Normally the secretion of pancreatic juice is brought about by the 

 stimulation produced by the acid chyme as it enters the duodenum. 

 Therefore, any factor which produces an increased flow of gastric juice 

 such, for example, as water 2 will cause a stimulation of the pancreatic 

 secretion. The secretion of pancreatic juice is probably not due to a 

 nervous reflex as was believed by Pawlow but rather, as Bayliss and 

 Starling have shown, is dependent upon the presence, in the epithelial 

 cells of the duodenum and jejunum of a body known as prosecretin. 

 This body is changed into secretin through the hydrolytic action of the 

 acid present in the chyme. The secretin is then absorbed by the blood, 

 passes to the pancreas and stimulates the pancreatic cells, causing a 

 flow of pancreatic juice. The quantity of juice secreted under these 

 conditions is proportional to the amount of secretin present. The 

 activity of secretin solutions is not diminished by boiling, hence the 

 body does not react like an enzyme. Further study of the body may 

 show it to be a definite chemical individual of relatively low molecular 

 weight. It has not been possible thus far to obtain secretin from any 

 tissues except the mucous membrane of the duodenum and jejunum. 



This secretin mentioned above belongs to the class of substances 

 called hormones or chemical messengers. These hormones play a very 

 important part in the coordination of the activities of certain functions 

 and glands. Other important hormones are those elaborated by the 

 thyroids, the adrenals, the pituitary body (hypophysis) , the embryo and 



1 Under this head we will consider only such digestive processes as are brought about 

 by enzymes originating in the pancreas. In the following chapter on IntestinaJ Digestion 

 will be found a consideration of such enzymes as have a true intestinal origin. 



2 See chapter on Gastric Digestion. 



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