gallbladder
Muscular membranous sac under the liver that stores and concentrates bile. Pear-shaped and expandable, it holds about 1.7 fluid oz (50 ml). Its inner surface absorbs water and inorganic salts from bile, which becomes 5–18 times more concentrated than when it leaves the liver. The gallbladder contracts to discharge bile through the bile duct into the duodenum. Disorders include gallstones and inflammation (cholecystitis). Surgical removal of the gallbladder (cholecystectomy) has no serious side effects.
gallbladder [′gȯl‚blad·ər]
Gallbladder
A hollow muscular organ, present in humans and most vertebrates, which receives dilute bile from the liver, concentrates it, and discharges it into the duodenum. It also participates in the entero-hepatic (re)circulation of bile, and in secretion and removal of conjugated xenobiotics, including radiopaque substances taken orally or intravenously for diagnostic purposes. Although not a vital organ, it stores bile, regulates biliary tract pressures, and, when diseased, enhances precipitation of various constituents of the bile as gallstones.
The system of bile ducts lying outside the liver is known as the extrahepatic biliary tract. In humans (Illus.) right and left hepatic ducts empty into the common hepatic duct, which continues to the duodenum as the common bile duct, or ductus choledochus. The gallbladder and cystic duct thus appear to be accessory organs and therefore are removable. However, they are converted into main-line structures by the presence of a sphincter (sphincter of Oddi) at the choledochoduodenal junction. Tonic contraction of this sphincter between meals forces the bile to back up into the gallbladder.
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In most other vertebrates essentially similar relations exist except when the gallbladder is absent, but there is considerable variation in proportion and arrangement of ducts, including the pancreatic ducts. See Liver, Pancreas
In humans, evacuation of the gallbladder is accomplished by a trigger mechanism which is set off by the presence of fatty foods, meat, and hydragogue cathartics in the duodenum and upper jejunum. Absorption of these substances by the mucous membrane results in the release of cholecystokinin (CCK), a hormone which rapidly circulates in the bloodstream and simultaneously produces contraction of the gallbladder and relaxation of the sphincter of Oddi. The most effective food is egg yolk, which contains certain l-amino acids. Resorption of bile salts by the intestine stimulates secretion of bile for hours after a meal. See Digestive system
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