Although not essential to life or health, the gallbladder is the site and source of appreciable suffering and disease in humans. With its cystic duct, the gallbladder constitutes a blind-ended, lateral extension of the common bile duct. Besides acting as a reservoir for bile, the gallbladder concentrates and otherwise alters the composition of bile. See also Gallbladder.
Gallstones are round, oval, or faceted concretions formed within the gallbladder from the salts and pigment of bile. Although the mechanism and reason for their formation are not clearly understood, the major predisposing factors are stasis (prolonged retention of bile in the gallbladder), abnormal composition of the bile (excessive amounts of cholesterol, bilirubin, or calcium), and infection. Passage of a gallstone through the ducts into the duodenum usually produces severe pain, called biliary colic. If a stone causes obstruction of the ducts, the result may be damage to the liver, pancreas, biliary system, and related structures either directly or through concomitant inflammation. Gallstones are rare in animals, although they have been found in nearly all species, especially in cattle. See also Bilirubin; Cholesterol; Cirrhosis.
Cholecystitis, or inflammation of the gallbladder, is a common disease in humans. It is nearly always associated with gallstones and is particularly common in obese middle-aged women. It is rare in animals. Most cases are thought to be the result of chemical irritation caused by excessively concentrated bile, which is in turn the result of partial or complete obstruction to the outflow of bile. Prolonged or recurrent episodes of inflammation result in chronic cholecystitis, characterized by thickening and scarring of the wall, contraction, and impairment of normal function.
Malignant tumors in the gallbladder are almost invariably associated with the presence of gallstones. Because they produce little in the way of symptoms, and because they very soon invade the liver, these tumors are rarely curable by surgical therapy at the time they are discovered. Benign tumors of the gallbladder and ducts are rare in humans, and in animals both benign and malignant tumors of these sites are extremely uncommon. See also Liver disorders.
