SMALL INTESTINE 157 



We shall view the histology of this organ from a physiological 

 standpoint, considering: (1) Those structures concerned in the 

 wretion of the succus entericus; (2) Those portions concerned in 

 absorption of food. 



JIISTOLOGY OF THOSE PARTS OF THE SMALL INTESTINE PARTICU- 

 LARLY CONCERNED IN THE PRODUCTION OF THE 

 SUCCUS ENTERICUS. 



The diagram (Fig. 104) is intended to represent at A the thick- 

 ness of the mucosa with its papillary elevations the villi. The 

 miiscularis mucosas B, from which the villi arise, separates the 

 mucosa from the snbmucosa C. The horizontal line at the bottom 

 of the diagram indicates the outer limit of C and the beginning of 

 the circular muscular coat of the intestine. The villi, everywhere 

 covered with columnar epithelium, often containing goblet -cells, 

 are represented in the drawing as widely separated. The crypts of 

 Lieberkiihn, which are lined by columnar epithelium, open between 

 the prominences. In the interior of each villus is a fine network 

 of Hood -capillaries (G, G). (In the specimen from which the 

 sketch was made the blood-vessels had been injected with colored 

 gelatin to make them prominent.) The cells on the borders of 

 the crypts secrete certain fluid material from the blood circulat- 

 ing in the capillary plexuses, and pour it out into the crypts ; 

 the crypts becoming filled with the fluid, the latter overflows and 

 passes into the lumen of the gut, to act in promoting digestion. 

 This is one source of the succus entericus, and there is yet another. 



Between the bases of some of the villi, tubes or ducts will be 

 found which, piercing the muscularis mucosae, reach the sub- 

 mucosa, where they branch, become convoluted, are lined with 

 secreting cells, and are known as the glands of Brunner. They 

 occur in the duodenum and are continuations of the pyloric glands 

 of the stomach. These glands are surrounded by blood -capillaries, 

 and the gland -cells secrete a fluid which is poured into the gut 

 between the villi, when it becomes mingled with the secretion 

 previously mentioned, and constitutes a part of the succus 

 entericus. 



We have, 'then, seen that the succus entericus is secreted partly 

 from the epithelial cells lining the crypts of Lieberkuhn, and partly 

 from the cells of Brunner J s glands. 



