The gallbladder is found right under the liver on the right side of the human body. It is pear-shaped, and its function is to store the bile that is manufactured by the liver.
The neck of the gallbladder is connected to a duct called the cystic duct. This duct in turn runs into the hepatic duct that comes from the liver. The joining of these two ducts creates the common bile duct. When a person digests food, bile flows from the liver through the common bile duct and into the duodenum. This structure is the last part of the stomach and the first part of the small intestine.
When bile isn't needed, it is kept from flowing into the duodenum by a muscle called the sphincter of Oddi. This muscle tightens around the opening of the duct and keeps the bile inside of the gallbladder. All the while, however, the liver is still producing bile. When bile is needed, the gallbladder is made to contract through a hormone called cholecystokinin, which is produced in the upper part of the small intestine.
Gallbladder diseases are rather common. Sometimes, when bile is stalled in the gallbladder, it concentrates and can turn into gallstones. This condition might necessitate the removal of the gallbladder.