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.
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The cystic duct connects the gall bladder to the common hepatic duct to form the common bile duct. This common bile duct then joins the pancreatic duct, and enters through the hepatopancreatic ampulla at the major duodenal papilla.
After being stored in the gallbladder the bile becomes more concentrated than when it left the liver, increasing its potency and intensifying its effect on fats. Most digestion occurs in the duodenum.
Vertebrates have gallbladders, but invertebrates don't. This is because vertebrates eat in boluses while invertebrates are constantly eating. To digest a large bolus of food requires a large amount of digestive secretions, hence the presence of a gallbladder.