CHAPTER VII. 

 DIGESTION (Cont'd). 



Intestinal Digestion: The Movements of the Intestines: 

 Absorption. 



The Secretion of Bile and Pancreatic Juice. Besides caus- 

 ing reflex closure of the pyloric sphincter, the contact of the 

 chyme, which is the name given to the semi-digested food as it 

 leaves the stomach, with the duodenal mucosa inaugurates the 

 processes of intestinal digestion by exciting the secretion of bile 

 and pancreatic juice. Neither of these juices is secreted into the 

 intestine during fasting; but both begin to flow very soon after 

 taking food, and they gradually increase in amount for about 

 three hours, and then rapidly decline. The bile at first comes 

 mainly from the gall bladder, in which it has accumulated dur- 

 ing fasting. When the gall bladder supply is exhausted, the bile 

 comes directly from the liver without entering the gall bladder, 

 and this secretion becomes more and more marked as digestion 

 proceeds. The storage of bile which occurs during fasting is 

 necessitated by the fact that although it is not required in the 

 intestine, bile is nevertheless being constantly produced by the 

 liver, because it is an excretory product, as well as a digestive 

 fluid: It must, therefore, be got rid of from the blood, but, be- 

 ing also useful for digestion, it is stored until it is required to 

 assist in this process. 



The sudden discharge of bile from the gall bladder is depen- 

 dent upon a nerve reflex excited by the contact of the acid chyme 

 with the duodenum. The increased secretion of bile from the 

 liver, like the secretion of pancreatic juice, is however, inde- 

 pendent of nerves, for it has been found that the application of 

 weak hydrochloric acid to the duodenum causes the juices to flow 

 after all the nerves, but not the blood vessels of the duodenum 

 have been cut. The only way by which such a result can be ex- 

 plained is by assuming that the acid causes some chemical sub- 



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