The Digestive System - 311 



DIAPHRAGM 



STOMACH 



i \ - I SPLEEN 



V\ S / PANCREAS 



SMALL INTESTINE 

 D_ DESCENDING COLON 



APPENDIX 



RECTUM I 



JKotf t Pdnwtn 



Fig. 16-24. Abdominal part of the human digestive tract (semidiagrammatic). 



denum occupies a fixed position in the 

 abdominal cavity, because it is attached di- 

 rectly to the dorsal body wall. All other parts 

 of the small gut, in contrast, enjoy some free- 

 dom of movement, because they are sus- 

 pended to the dorsal body wall by a thin, 

 transparent, sheetlike membrane, the mesen- 

 tery. This mesentery also provides a connec- 

 tion between the intestine and the body wall, 

 through which nerves and blood vessels pass 

 to and from these otherwise isolated parts. 



Fig. 16-25. Magnified view of the inside surface of 

 the small intestine showing the numerous villi. 



The second and third parts of the small 

 intestine are, respectively, the jejunum and 

 the ileum. The jejunum is about 10 feet in 

 length, and displays a greater number of the 

 intestinal glands and a lesser number of 

 villi than the ileum. The ileum ter- 

 minates abruptly in the lower right region 

 of the abdominal cavity, at which point 

 it joins the colon, or large intestine (Fig. 

 16-24). 



Relations of the Duodenum to the Liver and 

 Pancreas. Each small sample of the chyme 

 passes from the stomach into the duodenum, 

 whereupon it immediately encounters a 

 copious flow of both the pancreatic juice and 

 the bile. These two juices flow into the duo- 

 denum together, because the bile duct and 

 pancreatic duct join each other, forming a 

 short common duct that penetrates the duo- 

 denal wall (Fig. 16-24). 



The Pancreatic Juice. The inorganic com- 

 ponents of the pancreatic juice are mainly 

 water (about 98 percent by weight), and 

 various inorganic salts. Among these salts 

 there is an unusually high concentration of 

 the alkaline salt, sodium bicarbonate, which 



