The common bile duct (CBD) is an important part of the gastrointestinal tract responsible for carrying bile from the liver and gallbladder down to the duodenum, the first section of the small intestine. Duct denotes a tube-like structure coming from an organ in the body, usually carrying fluids. From the liver, two hepatic ducts join to form a common hepatic duct, and from the gallbladder comes the cystic duct. At the junction where the common hepatic duct and the cystic duct join is the beginning of the common bile duct. This bile duct is longer in length and wider in diameter compared to the other ducts.
The end of the common bile duct is joined by the pancreatic duct from the pancreas before they open into the duodenum. There is a ring-like muscle called the sphincter of Oddi around the end of the CBD. It acts to regulate the flow of bile and pancreatic juice into the duodenum and prevents the flow of duodenal contents back into the duct.
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Bile is formed in the liver and is essential in the digestion of fats and for carrying waste products from the liver to be excreted out of the body. Some of the bile is stored in the gallbladder to be released for the break down of fats, usually after eating. From the liver and gallbladder, bile goes down to the common bile duct to drain into the duodenum, where fat digestion can take place. Waste products carried by bile are sent to the duodenum as well, to be excreted out of the body through defecation. It is the presence of bile which makes the color of stool brown.
Stones from the gallbladder may pass down to the CBD in a condition called choledocholithiasis, and may cause obstruction if they cannot pass through the sphincter of Oddi. As the obstruction progresses, the duct becomes dilated. Symptoms of CBD obstruction include jaundice or yellowing of the skin and eyes, pain in the right upper abdomen, nausea, and vomiting. An ultrasound is usually performed to evaluate the area for the presence of stones. Risk factors for gallstone formation include obesity, genetic predisposition, and a diet high in fats.
As an obstruction causes bile to stagnate, bacteria may contaminate the area and multiply, and sometimes they can reach the bloodstream. If this occurs, it can be life threatening. Treatment for CBD obstruction usually includes surgery or endoscopic retrograde cholangiopancreatogram (ERCP) for the removal of stones. Administration of antibiotics is often done if infection has set in.