|Digestive system diagram showing the bile duct|
|ERCP image showing the biliary tree and the main pancreatic duct.|
A bile duct is any of a number of long tube-like structures that carry bile.
Bile, required for the digestion of food, is secreted by the liver into passages that carry bile toward the hepatic duct, which joins with the cystic duct (carrying bile to and from the gallbladder) to form the common bile duct, which opens into the intestine.
The biliary tree (see below) is the whole network of various sized ducts branching through the liver.
The path is as follows: Bile canaliculi → Canals of Hering → interlobular bile ducts → intrahepatic bile ducts → left and right hepatic ducts merge to form → common hepatic duct exits liver and joins → cystic duct (from gall bladder) forming → common bile duct → joins with pancreatic duct → forming ampulla of Vater → enters duodenum
Common bile duct 
Bile duct is green like the gallbladder, because of bile stains.
Blockage of the bile duct by a cancer, gallstones, or scarring from injury prevents the bile from being transported to the intestine and the active ingredient in the bile (bilirubin) instead accumulates in the blood. This condition results in jaundice, where the skin and eyes become yellow from the bilirubin in the blood. This condition also causes severe itchiness from the bilirubin deposited in the tissues. In certain types of jaundice, the urine will be noticeably darker, and the stools will be much paler than usual. This is caused by the bilirubin all going to the bloodstream and being filtered into the urine by the kidneys, instead of some being lost in the stools through the ampulla of Vater.
Jaundice is commonly caused by conditions such as pancreatic cancer, which causes blockage of the bile duct passing through the cancerous portion of the pancreas; cholangiocarcinoma, cancer of the bile ducts; blockage by a stone in patients with gallstones; and from scarring after injury to the bile duct during gallbladder removal.
Biliary drainage is performed with a tube or catheter (called a biliary drain, biliary stent or biliary catheter) by a surgeon or, commonly, an interventional radiologist. It can be used to relieve a blockage in the bile duct, either permanently or as a temporary solution before definite treatment such as surgery. The drain can be placed percutaneously through the liver, with the procedure then being called percutaneous transhepatic biliary drainage (PTBD). This can additionally be performed as part of a percutaneous transhepatic cholangiography, then a form of interventional radiology. A biliary drain can also be used to take bile samples for diagnostic workup or disease monitoring, as well as providing a route of administration for medical substances.
- Sai JK, Suyama M, Kubokawa Y, Matsumura Y, Inami K, Watanabe S, Kirino E. (2010). Identification of cerebral response to balloon distention of the bile duct. World J Gastroenterol. 16(14):1772-5. doi:10.3748/wjg.v16.i14.1772 PMID 20380011
- Biliary Drain Patient information from The Ohio State University Medical Center. Retrieved May 2011
- Kuhn, J. P.; Busemann, A.; Lerch, M. M.; Heidecke, C. D.; Hosten, N.; Puls, R. (2010). "Percutaneous Biliary Drainage in Patients with Nondilated Intrahepatic Bile Ducts Compared with Patients with Dilated Intrahepatic Bile Ducts". American Journal of Roentgenology 195 (4): 851–857. doi:10.2214/AJR.09.3461. PMID 20858809.
- The Cholangiocarcinoma Foundation
- The Johns Hopkins Gall Bladder & Bile Duct Cancer Web page
- bile+duct at eMedicine Dictionary
- Bile Ducts at the US National Library of Medicine Medical Subject Headings (MeSH)
- Measuring bile duct hyperplasia in toxicology