DUODENUM. 



2CX 



Intestinal glands. 



Longitudinal 

 section. 



of the intestinal glands, or may pass between them to the surface. In form 

 and position the duodenal glands suggest those of the oesophagus, but in 

 structure they so resemble the pyloric glands as to have been considered 

 identical with them. They produce a mucus which stains with difficulty, 

 and are free from goblet cells. As in the pyloric glands, occasional parietal 

 cells have been observed, found chiefly inside of the muscularis mucosae. 

 The dark cells due perhaps to compression, occur, and there are intercellular 

 secretory capillaries. A structureless basement membrane surrounds the 

 tubules. The duodenal glands are 

 so numerous toward the stomach that 

 the submucosa may be filled with their 

 tubules. They are also abundant near 

 the duodenal papilla where the bile and 

 pancreatic ducts enter the descending 

 portion of the duodenum. Beyond this 

 point they become fewer, and disappear 

 before the end of the duodenum is, 

 reached. Except for these glands the 

 duodenum is essentially like the remain- 

 der of the small intestine, described in 

 the following section. 



SMALL INTESTINE JEJUNUM AND 



ILEUM. 



As already stated, the small intes- 

 tine is characterized by its glands and 

 the villi which impart a velvety appear- 

 ance to its surface. In the jejunum 

 the club-shaped or cylindrical villi are 

 more slender and numerous than in the 

 ileum; in the distal portion of the latter 

 they are short and scattered, finally dis- 

 appearing on the colic surface of the valve of the colon [ileo- 

 caecal valve]. Each villus consists of an epithelial covering and a core 

 of connective tissue, the tunica propria (Fig. 231). There are other and 

 larger elevations in the lining of the small intestine, known as circular folds 

 (plicae circulares) [valvulae conniventes]. As shown in Fig. 232, their 

 interior is formed by the submucosa and their surface is covered by the 

 entire mucous membrane, villi, glands, and the muscularis mucosae. 

 Since the tunica muscularis does not enter them they cannot be obliterated 

 by distending the intestine. The circular folds begin in the duodenum 



Transverse 

 section 



Longitudinal 

 section 



of the tubules of a duodenal gland. 



FIG. 230. FROM A SECTION OF A HUMAN 

 DUODENUM. X 240. 



Only the lower half of the mucosa and upper 

 half of the submucosa are sketched. A 

 large portion of the duodenal glandjies 

 above the muscularis mucosae. 



