96 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



It is the fundus, and not the pylorus, which serves as a reservoir 

 and in which the greater part of gastric digestion occurs. The 

 precise condition of the pyloric sphincter during gastric digestion 

 is unknown. It may have simply an exalted degree of tonicity 

 which does not completely close the opening and which can be 

 overcome by pressure, or it may be tightly contracted and require 

 a distinct nervous dispensation to effect its relaxation for the 

 passage of fluids as well as solids. It would seem that the length 

 of time for which food is detained in the stomach depends more 

 upon its physical condition than upon its chemical that is, 

 that upon any stage of digestion which it may have reached; 

 for it can be shown that fluids pass very quickly into the 

 intestine. 



The secretory occurrences during these movements are of the 

 greatest importance (see p. 86-88). 



Nerve Supply. The stomach is supplied with pneumogastric 

 and sympathetic fibers. The latter can be traced through the 

 solar plexus, splanchnics and cervical ganglia to the spinal cord. 

 They exert an inhibitory effect on the muscular tissues; their 

 stimulation causes relaxation. The vagus fibers are motor; 

 their stimulation causes contraction. But these nerves serve only 

 to regulate the muscular movements. It is the stimulus of food in 

 the stomach which excites gastric peristalsis. It is not stopped 

 by section of these nerves, though it may be interfered with. 

 This stimulation is exerted either directly upon the nerve fibers 

 or upon the ganglia of the' stomach wall. 



The conditions influencing gastric digestion operate mainly 

 through changes in the quality and quantity of gastric juice. 



Digestion and Absorption in the Intestines. 

 The Small Intestine. 



Anatomy. The small intestine extends from the pylorus to 

 the caput coli, and is about twenty feet in length. It lies in 



