DIGESTION 



317 



Bile 



Bile is continuously produced by liver cells. It is collected by a series 

 of ducts from these sources and stored in the gall bladder (some animals, 

 e.g., the rat, do not have a gall bladder, and consequently the bile is 

 also stored in the liver cells). The pH of liver bile is about 8-8.6, while 

 that of the gall bladder is around 7. The main components of bile are 

 bile salts, bile pigments, cholesterol, and lecithin. 



An inspection of the formulas of the principal bile acids reveals that 



CONHCH.COOH 

 ^^ . ' 



Glycine 



Cholic acid 



Glycocholic acid 



they are related to the sterols (p. 95). The prefix glyco or tauro is 



Cholic acid 



Taurocholic acid 



used to show that the sterol portion of the bile acid (cholic acid in the 

 above structures) is combined by a peptide linkage with glycine or 

 taurine, respectively. Glyco and taurodesoxycholic acids have been iso- 

 lated (the hydroxyl group in carbon 7 of cholic acid is replaced by a 

 hydrogen in desoxy cholic acid) from bile. Similar ccmjugates of cheno- 

 desoxycholic acid (hydroxyl of cholic acid in position 12 replaced by 

 hydrogen) and lithocholic acid (hydroxyls of cholic acid in carbons 7 

 and 12 replaced by hydrogens) have been demonstrated to be present 

 in bile. The sterol portion of the bile acids have a great affinity for 



