CH. XXXII I.] 



THE GASTRIC GLANDS 



509 



duodenum the pyloric glands become larger, more convoluted and 

 more deeply situated. They are directly continuous with Brunner's 

 glands in the duodenum. 



The central cells of the fundus glands and, to a less degree, the 

 cells of the pyloric glands, are loaded with granules. During secre- 

 tion they discharge their granules, those that remain being chiefly 

 situated near the lumen, leaving in each cell a clear outer zone. These 

 are the cells that secrete the pepsin. Like secreting cells generally, 

 they pump water from the lymph that bathes them into the lumen ; 



FIG. 356. Section showing the 

 - pyloric glands, s, Free sur- 

 face ; d, ducts of pyloric glands ; 

 n, neck of same ; m, the gland 

 tubules ; mm, muscularis mu- 

 cosae. (Klein and Noble Smith.) 



FIG. 357. Plan of the blood-vessels of the 

 stomach, as they would be seen in a 

 vertical section, a, Arteries, passing 

 up from the vessels of submucous 

 coat ; b, capillaries branching between 

 and around the tubes ; c, superficial 

 plexus of capillaries occupying the 

 ridges of the mucous membrane; 

 d, vein formed by the union of veins 

 which, having collected the blood of 

 the superficial capillary plexus, are 

 seen passing down between the tubes. 

 (Brinton.) 



to this certain materials are added which are formed by the proto- 

 plasmic activity of the cells. The most important substance in a 

 digestive secretion is the enzyme. In the case of the gastric juice 

 this is pepsin. We can trace an intermediate step in this process by 

 the presence of the granules in the cells. The granules are not, how- 

 ever, composed of pepsin, but of a mother-substance which is readily 

 converted into pepsin. We shall find similar enzyme precursors in 

 the cells of the pancreas, and the term zymogen is applied to these 

 enzyme precursors. The zymogen in the gastric cells is called 

 pepsinogen. The rennet-enzyme that causes the curdling of milk is 

 "formed by the same cells. 



