The gallbladder is a sac about 3 to 4 inches (7.5 to 10 cm) long located on the undersurface of the right lobe of the liver. Bile in the hepatic duct of the liver flows through the cystic duct into the gallbladder (see Fig. 16–6), which stores bile until it is needed in the small intestine. The gallbladder also concentrates bile by absorbing water.
When fatty foods enter the duodenum, the enteroendocrine cells of the duodenal mucosa secrete the hormone cholecystokinin. This hormone stimu-lates contraction of the smooth muscle in the wall of the gallbladder, which forces bile into the cystic duct, then into the common bile duct, and on into the duo-denum.