CHAPTER VI. 



DKiESTION (Cont'd). 



Digestion in the Stomach. 



The Secretion of Gastric Juice. After passing the cardiac 

 sphincter, the food collects in the fundus of the stomach. When 

 it is solid in consistency it becomes disposed in definite layers, 

 the first swallowed near the mucosa, the last swallowed in the 

 center. When, as is usual in man, the food is more or less fluid, 

 this layer formation is less evident and it collects in the most de- 

 pendent part of the body of the stomach (see Fig. 5). Within a 

 few minutes of the entry of the first portion of food, the glands 

 of the gastric mucosa begin to secrete their digestive juices. The 

 immediate exciting cause of this secretion is not the contact of 

 food with the mucosa although this acts later but is a ner- 

 vous stimulus transmitted to the stomach through the vagus 

 nerve 1 and coming from a nerve center situated in the medulla. 



The aetii'iti( s of Ihis y as trie ct nt< r arc called into operation by 

 afferent impulses in the nerres that lirminate in the taste buds 

 and olfactory epithelium. The process of gastric secretion is 

 therefore initiated in the mouth, and the stimulus that is re- 

 sponsible for it is the good taste and the flavor of the food. Just 

 as in the case of the salivary glands, the food, in order to excite 

 the secretion, need not actually enter the mouth for a psychologi- 

 cal stimulus may also act on the gastric center. Thus the sight 

 or smell of savory food, or even the hearing of some sound that is 

 known by experience to be associated with the gratification of 

 the appetite can call it forth. These important facts were first 

 of all revealed by observations through a gastric fistula made in 

 the case of a boy who. by swallowing strong alkali, was unable 

 to take food by the mouth because of stricture of the (esophagus ; 



i After cuttiny the vuyi, this secretion of yastric juice does not occur. 



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