Chap. 11 FOODS AND NUTRITION 191 



fatlike substance that the liver absorbs from the blood. Its removal does 

 not necessarily cause any digestive difficulties. 



Functions of Bile. Bile produces no digestive enzyme but it performs 

 several functions in the intestine. It supplies organic salts (bile salts) which 

 are the emulsifying salts of fats. Bile salts serve as specific activators of 

 pancreatic lipase. 



Important as bile is for the more efficient digestion of fats, it is still more 

 important for their absorption. If bile is prevented from entering the intestine, 

 a large proportion of the fatty acids passes out with the waste products in- 

 stead of being properly absorbed. This effect of the absence of the bile salts 

 has only recently been discovered. Bile salts unite with the fatty acids and 

 form compounds that pass into the lining cells of the intestine. Here the bile 

 salts are separated from the compounds, enter the blood capillaries, and are 

 carried to the liver where they are picked up by the liver cells and once more 

 go into the bile. The fatty acids that were freed from the bile salts combine 

 with glycerin (absorbed by the lining cells) to form neutral fat. The greater 

 part of this fat passes into the microscopic lymphatic vessels, the lacteals, in 

 the centers of the intestinal villi (Figs. 11.19, 11.20). It eventually enters the 

 blood by way of the lymph. 



Bile salts make possible the absorption of the antihemorrhagic vitamin K, 

 which occurs in spinach, cabbage, and other green foods (Table 11.1). In 

 the treatment of obstructive jaundice, when the bile ducts may be clogged 

 by gallstones and no bile enters the intestine, the usual tendency toward 

 bleeding is countered by doses of bile salts. Chickens develop a hemorrhagic 

 disease if they do not get any grass or other green foods. 



Functions of the Pancreas. The pancreas Hes between the stomach and 

 duodenum (Fig. 1 1.17). It is an irregularly shaped gland composed of groups 

 of lobules that make the surface look bubbly. In each lobule the cells are 

 arranged around a minute drainage tubule. These tubules unite with one 

 another and finally form the main pancreatic duct. This carries the secretion 

 to the intestine, emptying into it through a common opening with the bile 

 duct. Scattered through the pancreas are the entirely different glands called 

 the islands of Langerhans. Their hormone, insulin, is secreted directly into 

 the blood and is necessary for the utilization of sugar in the body, the safe- 

 guard against sugar diabetes (diabetes mellitus). 



The pancreatic juice is a clear alkaline fluid secreted on an average of 

 about a liter (1.05 liquid quarts) per day. Its principal enzymes are: tryp- 

 sinogen, which, when converted into trypsin, carries the digestion of proteins 

 a step beyond that occurring in the stomach; amylopsin (pancreatic amylase) 

 which completes the digestion of starch begun in the mouth, and steapsin 

 (pancreatic lipase) which splits fats into fatty acids and glycerol. Pancreatic 

 secretion collected directly from the ducts has very little power to digest 



