Composition and circulation of the bile

Bile is an essential fluid that delivers bile acids, lipids, and metabolites to the intestine. It is formed by a complex mechanism that requires hepatocyte secretion of bile acids and other solutes, such as glutathione and bicarbonate, and bile ductular secretion of bicarbonate. Approximately 95% of bile acids is recovered from the intestine and then reused (enterohepatic circulation). Although there is a small amount of passive absorption of bile acids in the proximal small intestine, the major site of absorption is the distal ileum where there is an active bile acid transport mechanism. Much of what we know about hepatocyte transport mechanisms that are essential for the enterohepatic cycling of bile acids has been learned from patients with specific inheritable defects in this process. Discovery of the transporters mediating enterohepatic cycling has opened new windows into diagnosis and treatment of hepatobiliary disorders.