TITE DTCKSTIVE SYSTEM 



277 



plexus delicate fibrils pass to their terminations in submucosa, mus- 

 cularis mucosee, and mucous membrane. 



Secretion and Absorption 



The secretory activities of ci)ithchal cells have already been men- 

 tioned (page 217). The epitheHum of the gastro-intestinal tract 

 must be considered as having two main functions: (i) The secretion 

 of substances necessary to digestion; and (2) the absorption of the 

 products of digestion. 



(i) Secretion. — The production of mucus takes place in the 

 mucous or goblet cell, which is present throughout the gastro- 

 enteric mucosa and, as already mentioned, probably represents a 

 differentiation of the ordinary columnar epithelial cell. The chief 

 cells, "peptic cells," of the 

 stomach glands are compar- 

 atively clear during fasting, 

 with development of ergas- 

 toplasm in their basal ends. 

 With the onset of digestion 

 these cells increase in size 

 and become generally cloudy 

 from development of gran- 

 ules with reduction of the 

 ergastoplasm. These gran- 

 ules represent a pre-ferment 

 or pepsinogen and with 

 their discharge into the 

 lumen of the gland, the cells 

 again become smaller, clearer, and assume the resting condition. 

 Bensley and Theohara have recently very clearly demonstrated the 

 secretory chain in the chief cells from ergastoplasm or basal filaments 

 through pepsinogen granules to pepsin. While some authorities 

 still contend that a minor pepsin-forming role is played by the 

 pyloric glands, the above facts together with the fact that activity 

 of the chief cells (Fig. 180) is coincident with an increase in the pepsin 

 found in the stomach, and that the amount of pepsinogen in the gastric 

 mucosa is proportionate to the number of granules in the chief cells 

 (Langley and Sewell) , may be accepted as proving these cells the main 

 if not the sole producers of pepsin, and the granules as some stage 

 in the elaboration of the ferment. As their name of "acid cells" 





Fig. 1 70. — Section through Glands of Fundus 

 of Human Stomach in Condition of Hunger. 

 X500. (Bohm and von Davidoff.) <7, Stroma; 

 b, parietal cell; c, lumen; d, chief cell. 



