The gallbladder (Figure 11.9) is a pear-shaped organ in close contact with the inferior surface of the liver. The cystic duct of the gallbladder joins with the com-mon hepatic duct to form the common bile duct. The function of the gallbladder is to store and concentrate bile that is secreted by the liver. The capacity of a normal gallbladder is about 40–70 mL (1.4–2.4 oz). Because the opening (sphincter) of the common bile duct is closed other than at meal times, the bile that is secreted by the liver is stored in the gallbladder.
When stored, some water from the bile is absorbed by the walls of the gallbladder, concentrating it. Con-traction of the smooth muscles of the gallbladder and opening of the sphincter is largely caused by chole-cystokinin, a hormone secreted by cells in the duo-denum.