126 DIGESTION 



independent of the act of swallowing and independent of 

 the vagus. 



Two conditions in the stomach notably increase the 

 tonus of the cardiac orifice and inhibit its rhythmic relaxa- 

 tion — mechanical irritation and the presence of free acid 

 in the cardiac sac, 



THE STOMACH 



The functions of the stomach are principally to act 

 as a reservoir from which food can be discharged into the 

 intestine at a regular speed, and to begin the breakdown 

 of foodstuff and, in particular, of proteins. It possesses 

 but a shght absorptive power. 



Form of the Stomach 



The stomach consists essentially of two portions, the 

 cardiac and the pyloric, separated by the incisura angularis. 

 The cardiac portion is further divided into two parts, the 

 fundus or part above the level of the cardiac orifice, and the 

 body or part below the fundus. Similarly, the pyloric 

 part is subdivided into the pyloric vestibule — the main 

 proximal part — and the pyloric canal, which consists of 

 the distal 3 cm. and terminates at the pyloric sphincter. 



The cardiac and the pyloric part of the stomach differ 

 in their shape, in the structure of the glands which hne 

 them, in the character of the fluid which they secrete, and 

 in the movements which they undergo. 



All the gastric glands secrete pepsin, the principal 

 gastric enzyme, but only those of the cardiac part secrete 

 free hydrochloric acid, which is beheved to be formed in 

 the oxyntic cells. 



The muscles of the stomach-wall are disposed in three 

 layers — - 



1, An outermost longitudinal layer continuous with the 

 corresponding layer in the oesophagus, but separated by a 

 fibrous band from the longitudinal layer of the duodenum, 



2. A middle circular layer forming a complete wall. It 



