Gallbladder

The gallbladder is a muscular sac located in a shallow fossa on the inferior surface of the liver, measuring about 10 cm in length and roughly the size of a kiwi fruit. It has a pear-like shape with three distinct regions: the fundus, the central body, and the tapered neck. The cystic duct extends from the gallbladder's neck and unites with the common hepatic duct to form the common bile duct.

The gallbladder's primary function is to store and concentrate bile, a fluid produced by the liver that aids in digestion. When the duodenum receives partially digested chyme from the stomach, the gallbladder contracts to expel bile into the cystic duct, which then travels via the common bile duct to reach the duodenum for mechanical and chemical digestion in the small intestine.

The gallbladder can expand as it fills with bile thanks to its honeycomb-like mucosal folds, which are similar to rugae in the stomach. When empty, these folds collapse, but they unfold and stretch as bile accumulates, allowing the gallbladder to hold approximately 40 to 70 mL of bile without tearing.

As bile remains in the gallbladder, its composition changes as water is absorbed through the gallbladder's mucosa. This absorption process increases the concentration of bile salts and other components, making the stored bile more potent for breaking down fats during digestion.

Gallstones form when bile becomes excessively concentrated, causing insoluble minerals and salts to crystallize. Small gallstones are usually excreted without issue, but larger ones can damage the gallbladder wall or block the cystic duct, potentially leading to diseases of the liver and gallbladder that require medical attention.

The cystic duct extends from the gallbladder's neck and unites with the common hepatic duct to form the common bile duct. This combined duct serves as the final pathway for bile to travel from both the liver and gallbladder into the duodenum during digestion.

The gallbladder has a muscular wall that contracts in response to the presence of partially digested chyme in the duodenum. This muscular contraction forces stored bile into the cystic duct, allowing it to flow through the common bile duct and into the small intestine where it aids in fat digestion.