Gallbladder and Bile Duct Diseases

Bile Production

Bile is an isotonic fluid whose electrolyte composition resembles that of blood plasma. It is produced by the liver and contains bile acids, bilirubin, cholesterol, phospholipids, and electrolytes. Soluble bile acids, the major solute components of bile (80 percent), are synthesized from water-insoluble cholesterols. The primary bile acids are cholic acid and chenodeoxycholic acid (CDCA). They are formed by conjugating glycine or taurine into cholesterol molecules.

Bile Secretion

Bile formed in the hepatic lobules are secreted into a network of bile ducts that eventually forms the right and the left hepatic ducts. The two hepatic ducts then converge to form the common hepatic duct. Off of the common hepatic duct is the gallbladder which is connected via the cystic duct. The cystic duct and the common hepatic duct join together to form the common bile duct, which enters the duodenum through the ampulla of Vater. Joining the ampulla are pancreatic ducts, through which exocrine pancreatic secretions are made. The sphincter of Oddi surrounds the common bile duct and the pancreatic duct.

During fasting state, bile is secreted by the liver and about 50 percent of the secreted bile flows into the gallbladder via the cystic duct and is stored there. The remaining secretion flows into the common bile duct and is trapped in the duct due to the constriction of the sphincter of Oddi. The bile secretion that is stored in the gallbladder is highly concentrated because up to 90 percent of the water in the secretion are absorbed in the gallbladder. When an individual eats and food enters the duodenum, a series of hormonal and neuronal processes are activated that causes the contraction of the gallbladder and the relaxation of the sphincter of Oddi.

Cholelithiasis

Cholelithiasis is the formation or the presence of calculi in the gallbladder. Gallstone is the most frequent cause of clinical disorders relating to extrahepatic biliary tracts. In the United States, it is estimated that at least 20 million individuals have gallstones and the incidence of cholelithiasis is 1 million per year. More than 500,000 cholescystectomies are performed each year. Gallstones are divided into two major types: cholesterol stones and pigment stones. The predominant composition of cholesterol stones is cholesterol monohydrate, while pigment stones primarily are composed of calcium bilirubinate.

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