THE DIGESTIVE SYSTEM 



The columnar cells are peculiar in that they possess a charac- 

 teristic striated cuticular border when examined under moderately 

 high magnification. They possess a finely reticular cytoplasm and 

 an ovoid nucleus which is situated at the proximal end or base of 

 the cell. Frequently the cytoplasm contains droplets of fat which 

 are in process of absorption. Occasional leucocytes find their way 

 into the epithelial coat, whence they may penetrate the intercellu- 

 lar substance and enter the intestinal canal. 



The intestinal glands include two types, the tubulo-acinar 

 glands of Brunner and the simple tubular glands of Lieberklihn. 

 The former occur only in the duodenum ; the latter are found in 

 all portions of the intestine from the pylorus to the rectum. 



THE GLANDS OF LIEBERKUHN (mucous crypts) are simple 

 tubules which extend the whole depth of the mucous membrane 

 and open upon the free surface between the bases of the villi. 

 Hence the lining epithelium of the glands becomes continuous 

 with that which clothes the villi. The mucous crypts are embedded 

 in the diffuse lymphoid tissue of the corium ; they rarely branch. 

 They consist of a lining epithelium and a basement membrane. 



The epithelium of the crypts contains three types of cells : 1, 

 columnar cells ; 2, gollet cells ; and 3, the granule cells of Paneth. 

 The columnar and goblet cells resemble those which clothe the 

 villi. The columnar cells which line the neck of the crypts pos- 

 sess a very indistinct cuticular border which is not found in the 

 fundus cells of the glands. The epithelium of the crypts appears 

 to take no part in the process of absorption and therefore contains 

 no fat globules. 



At the neck of the gland the epithelium frequently contains 

 mitotic figures which have been demonstrated in man (Schaffer *) 

 as well as in the lower mammals (Bizzozero f). Little or no mito- 

 sis has been demonstrated in the fundus of the gland or upon the 

 free surface of the villi. On these facts the so-called "wander 

 theory " of Bizzozero is founded. According to this theory there 

 exist in the neck of the crypts certain indifferent cells which are 

 capable of reproduction by mitosis and whose daughter cells move 

 toward the free surface, being at the same time differentiated into 

 either the goblet or the columnar cells of the villi. 



Bizzozero originally considered that the granule cells of Paneth 

 at the fundus of the crypts were intermediate phases in the for- 

 mation of goblet cells, but as there is little or no mitosis in the 

 * Sitz. d. k. Akad. Wissensch., Wien, 1897. f Arch - f - path. Anat., 1887. 



