FOODS AND NUTRITION 



189 



Chap. 11 



important region into which the ducts of the liver and pancreas open. This 

 U-shaped bend is the duodenum, an old-time name meaning 12, given it be- 

 cause in man it is about the length of 12 fingers. Except in the duodenal 

 region, the intestines are loosely attached to the dorsal body wall by mesentery 

 (Fig. 11.18). 



Function of the Liver and the Gall Bladder. Among its many other activities, 

 the liver secretes the bile, vitally important in digestion although it contains 



Thorocic 

 covity 



Pancreos 



Abdominol 

 cavity 



Gall blodder 



Bile duct 



Poncreotic ducf 



Fig. 11.17. Diagram showing the human liver and stomach beneath the di- 

 aphragm, and ducts from the liver, gall bladder and pancreas leading through one 

 opening into the intestine. 



no enzymes. All the blood in the body passes through the liver several times 

 per hour; thus it maintains a content of about one-fifth of the body's total 

 blood supply. 



Microscopic bile capillaries so permeate the liver that they are in contact 

 with every cell. These capillaries join to make the larger hepatic ducts, which 

 in turn form the main bile duct to the duodenum. The gall bladder, a tempo- 

 rary storage place for bile and part of a remarkable mechanism, branches 

 from the main duct. As it is produced bile passes into the bile duct, but is 

 ordinarily kept from passing into the intestine by the continued contraction 

 of a band of muscle that encircles the opening of the bile duct into the 

 intestine. When the duct is filled, the bile is forced back into the gall bladder 

 where it is stored until required, in the meantime becoming more concen- 

 trated by loss of water through the bladder wall. With the entrance of 

 food into the duodenum, the gall bladder contracts and discharges bile down 

 the duct whose circular (sphincter) muscle then relaxes, allowing the bile 

 to flow into the intestine. Although the gall bladder is controlled by the 

 parasympathetic part of the vagus nerves, experiments have proved that it 



