The cystic duct is a tube within the human digestive system that connects the gallbladder to the rest of the biliary tree. This network of ducts transports bile from the liver and gallbladder to the small intestine. The duct regulates the flow of concentrated bile, which is fundamental to the process of fat digestion.
Anatomical Placement of the Cystic Duct
The cystic duct is situated in the upper right quadrant of the abdomen, nestled beneath the liver alongside the gallbladder. It originates directly from the neck of the gallbladder, the organ’s tapered end. The duct then travels a short distance, typically measuring between two and four centimeters long, before merging with the common hepatic duct.
The union of the cystic duct and the common hepatic duct creates the common bile duct. Inside the cystic duct are specialized mucosal folds known as the spiral valves of Heister. These folds may help keep the duct open but are not considered active regulators of bile flow. The duct is generally narrow, often ranging from two to three millimeters in diameter.
Bile Regulation and Storage
The cystic duct acts as a two-way conduit for bile, facilitating both storage and controlled release. Bile, produced by the liver, travels through the common hepatic duct. When digestion is not active, the cystic duct allows bile to flow into the gallbladder for concentration and storage.
The gallbladder absorbs water from the bile, concentrating it before it is needed for a meal. When fatty food enters the small intestine, a hormone called cholecystokinin (CCK) is released, signaling the gallbladder to contract. Contraction pushes the stored, concentrated bile back out through the cystic duct and into the common bile duct. From there, the bile enters the small intestine to emulsify fats and aid in their absorption.
Involvement in Common Gallbladder Conditions
Because the cystic duct is the entry and exit point for the gallbladder, it is susceptible to blockages, which cause most gallbladder diseases. The most common issue involves gallstones, hardened deposits of digestive fluid components, usually cholesterol. Gallstones form inside the gallbladder, but symptoms arise when they migrate and become lodged in the narrow cystic duct.
A gallstone obstructing the duct prevents bile from leaving the gallbladder, causing pressure to build up inside the organ. This obstruction leads to acute cholecystitis, inflammation of the gallbladder, often accompanied by severe pain in the upper right abdomen. If the obstruction persists, it can lead to complications such as bacterial infection and tissue death. During a cholecystectomy (surgical removal of the gallbladder), the cystic duct is identified, clipped, and cut to detach the organ from the biliary system.