small pear-shaped sac that stores and concentrates bile
. It is connected to the liver (which produces the bile) by the hepatic duct. When food containing fat reaches the small intestine, the hormone cholecystokinin is produced by cells in the intestinal wall and carried to the gall bladder via the bloodstream. The hormone causes the gall bladder to contract, forcing bile into the common bile duct. A valve, which opens only when food is present in the intestine, allows bile to flow from the common bile duct into the duodenum where it functions in the process of fat digestion. Sometimes the substances contained in bile crystallize in the gall bladder, forming gallstones. These small, hard concretions are more common in persons over 40, especially in women and the obese. They can cause inflammation of the gall bladder, a disorder that produces symptoms similar to those of indigestion, especially after a fatty meal is consumed. If a stone becomes lodged in the bile duct, it produces severe pain. Gallstones may pass out of the body spontaneously; however, serious blockage is treated by removing the gall bladder surgically.
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