{{Short description|Organ system which creates, stores, and transports bile}} {{Use British English|date = February 2019}} {{Infobox anatomy | Name = Biliary tract | Image = Diagram showing the position of the perihilar bile ducts CRUK 357.svg | Caption = Ducts of the biliary tract | function = Facilitate movement of [[bile]], which aids in fat absorption }} The '''biliary tract''' (also '''biliary tree''' or '''biliary system''') refers to the [[liver]], [[gall bladder|gallbladder]] and [[bile ducts]], and how they work together to make, store and secrete [[bile]].<ref name=":2" /> Bile consists of water, [[electrolyte]]s, [[bile acid]]s, [[cholesterol]], [[phospholipid]]s and [[conjugated bilirubin]].<ref name=":3">{{Citation |last1=Hundt |first1=Melanie |title=Physiology, Bile Secretion |date=2022 |url=https://www.ncbi.nlm.nih.gov/books/NBK470209/ |work=StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29262229 |access-date=2022-11-14 |last2=Basit |first2=Hajira |last3=John |first3=Savio}}</ref> Some components are synthesized by [[hepatocyte]]s (liver cells); the rest are extracted from the blood by the liver.<ref>{{cite book | vauthors = Townsend C |title=Sabiston Textbook of Surgery |publisher=Elsevier |year=2022 |isbn=978-0-275-97283-7 |edition=21st |pages=1489–1527}}</ref>
Bile is secreted by the liver into small ducts that join to form the [[common hepatic duct]].<ref name=":4" /> Between meals, secreted bile is stored in the gallbladder.<ref name=":5" /> During a meal, the bile is secreted into the [[duodenum]] (part of the small intestine) to rid the body of waste stored in the bile as well as aid in the [[Digestion#Fat digestion|absorption of dietary fats and oils]].<ref name=":5">{{Citation |last1=Jones |first1=Mark W. |title=Physiology, Gallbladder |date=2022 |url=https://www.ncbi.nlm.nih.gov/books/NBK482488/ |work=StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29494095 |access-date=2022-11-03 |last2=Small |first2=Kaitlynn |last3=Kashyap |first3=Sarang |last4=Deppen |first4=Jeffrey G.}}</ref>
== Structure == {{Bile ducts and pancreas}} The biliary tract refers to the path by which bile is secreted by the liver then transported to the [[duodenum]], the first part of the [[small intestine]]. A structure common to most members of the [[mammal]] family, the biliary tract is often referred to as a tree because it begins with many small branches that end in the [[common bile duct]], sometimes referred to as the trunk of the biliary tree. The duct, the branches of the [[Common hepatic artery|hepatic artery]], and the [[hepatic portal vein|portal vein]] form the central axis of the [[portal triad]].<ref>{{Cite journal |last1=Jurkovich |first1=G. J. |last2=Hoyt |first2=D. B. |last3=Moore |first3=F. A. |last4=Ney |first4=A. L. |last5=Morris |first5=J. A. |last6=Scalea |first6=T. M. |last7=Pachter |first7=H. L. |last8=Davis |first8=J. W. |date=September 1995 |title=Portal triad injuries |journal=The Journal of Trauma |volume=39 |issue=3 |pages=426–434 |doi=10.1097/00005373-199509000-00005 |issn=0022-5282 |pmid=7473903}}</ref> Bile flows in the direction opposite to that of the blood present in the other two channels.<ref>{{Cite journal |last1=Wolkoff |first1=Allan W. |last2=Cohen |first2=David E. |date=February 2003 |title=Bile acid regulation of hepatic physiology: I. Hepatocyte transport of bile acids |journal=American Journal of Physiology. Gastrointestinal and Liver Physiology |volume=284 |issue=2 |pages=G175–179 |doi=10.1152/ajpgi.00409.2002 |issn=0193-1857 |pmid=12529265}}</ref>
The system is usually referred to as the biliary tract or system,<ref>{{MeshName|Biliary+tract}}</ref> and can include the use of the term "hepatobiliary" when used to refer just to the liver and bile ducts.<ref name=":2">{{cite book| vauthors = Dorland WA|title=Dorland's Illustrated Medical Dictionary|date=2012|publisher=Elsevier|isbn=978-1-4160-6257-8|page=846|edition=32nd}}</ref> The name biliary tract is used to refer to all of the ducts, structures and organs involved in the production, storage and secretion of bile.<ref>{{cite book| vauthors = Dorland WA |title=Dorland's Illustrated Medical Dictionary|date=2012|publisher=Elsevier|isbn=978-1-4160-6257-8|page=1946|edition=32nd}}</ref>
The tract is as follows: * [[Bile canaliculi]] >> [[Canals of Hering]] >> intrahepatic bile ductule (in portal tracts / triads) >> interlobular bile ducts >> left and right hepatic ducts<ref name=":4" /> * These merge to form the [[common hepatic duct]]<ref name=":4" /> * The [[common hepatic duct]] exits the liver and joins with the [[cystic duct]] from [[gall bladder]]<ref name=":4" /> * Together these form the [[common bile duct]] which joins the [[pancreatic duct]]<ref name=":4" /> * These pass through the [[ampulla of Vater]] and enter the duodenum<ref name=":4" />
== Function ==
Bile is secreted by the liver into small ducts that join to form the [[common hepatic duct]].<ref name=":3" /> Between meals, secreted bile is stored in the gall bladder, where 80–90% of the water and electrolytes can be absorbed, leaving the bile acids and cholesterol.<ref name=":5" /> During a meal, the smooth muscles in the gallbladder wall contract, causing bile to be secreted into the [[duodenum]] to rid the body of waste stored in the bile as well as aid in the [[Digestion#Fat digestion|absorption of dietary fats and oils]] by solubilizing them using [[bile acids]].<ref name=":5" />
==Clinical significance== [[File:Diagram showing the bile ducts in the pancreas CRUK 293.svg|thumb|Union of common bile duct and pancreatic duct terminating at duodenum (small intestine).]] [[Gallstone]]s can form within the gallbladder and get stuck within the biliary tract, leading to various diseases depending on the location of the stone.<ref name=":0" /> [[Gallstone|Gallstone disease]], or [[cholelithiasis]], is very common in the United States, impacting over 20 million people.<ref name=":0">{{Cite journal |last1=Lam |first1=Robert |last2=Zakko |first2=Alan |last3=Petrov |first3=Jessica C. |last4=Kumar |first4=Priyanka |last5=Duffy |first5=Andrew J. |last6=Muniraj |first6=Thiruvengadam |date=July 2021 |title=Gallbladder Disorders: A Comprehensive Review |journal=Disease-a-Month |volume=67 |issue=7 |article-number=101130 |doi=10.1016/j.disamonth.2021.101130 |issn=1557-8194 |pmid=33478678}}</ref>
Gallstones frequently occur without causing symptoms– this is known as [[Cholelithiasis|asymptomatic cholelithiasis]].<ref name=":0" /> Sometimes gallstones may get stuck in the [[cystic duct]], which serves as a bridge between the gallbladder and the [[common bile duct]], and can lead to inflammation in the wall of the gallbladder.<ref name=":0" /> This inflammation of the gallbladder is known as [[cholecystitis]] and is a common indication for surgical removal of the gallbladder, or [[cholecystectomy]].<ref name=":1">{{Citation |last1=Hassler |first1=Kenneth R. |title=Laparoscopic Cholecystectomy |date=2022 |url=https://www.ncbi.nlm.nih.gov/books/NBK448145/ |work=StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=28846328 |access-date=2022-11-03 |last2=Collins |first2=Jason T. |last3=Philip |first3=Ken |last4=Jones |first4=Mark W.}}</ref>
Occasionally gallstones may become lodged in the common bile duct and obstruct the flow of bile from the gallbladder to the small intestine– this condition is known as [[choledocholithiasis]]<ref name=":0" /> and is another indication for [[cholecystectomy]].<ref name=":1" /> The common bile duct, commonly abbreviated CBD, is formed by the union of the cystic duct and common hepatic duct, and it later joins the [[pancreatic duct]] to terminate in the [[Ampulla of Vater]] at the small intestine. The function of the common bile duct is to allow bile to travel from the gallbladder to the small intestine, mixing with pancreatic digestive enzymes along the way.<ref name=":4">{{Cite journal |last1=Vakili |first1=Khashayar |last2=Pomfret |first2=Elizabeth A. |date=December 2008 |title=Biliary anatomy and embryology |journal=The Surgical Clinics of North America |volume=88 |issue=6 |pages=1159–1174, vii |doi=10.1016/j.suc.2008.07.001 |issn=0039-6109 |pmid=18992589}}</ref> One possible complication of choledocholithiasis is an infection of the bile ducts between the liver and the gallstone lodged in the common bile duct. This condition is known as [[acute cholangitis]] and is commonly associated with a triad of clinical symptoms known as [[Charcot's cholangitis triad|Charcot's Triad]], which includes fever, right upper quadrant abdominal pain, and jaundice.<ref name=":0" /> This constellation of symptoms has a 96% specificity for cholangitis,<ref name=":0" /> and can be expanded upon with the addition of hypotension and altered mental status to form [[Reynolds' pentad|Reynold's Pentad]].<ref name=":0" />
The biliary tract can also serve as a reservoir for intestinal tract infections. Since the biliary tract is an internal organ, it has no [[somatic nervous system|somatic nerve supply]], and [[biliary colic]] due to infection and inflammation of the biliary tract is not a somatic pain. Rather, pain may be caused by luminal distension, which causes stretching of the wall. This is the same mechanism that causes pain in [[bowel obstruction]]s.<ref>{{cite journal | vauthors = Lin YM, Fu Y, Wu CC, Xu GY, Huang LY, Shi XZ | title = Colon distention induces persistent visceral hypersensitivity by mechanotranscription of pain mediators in colonic smooth muscle cells | journal = American Journal of Physiology. Gastrointestinal and Liver Physiology | volume = 308 | issue = 5 | pages = G434–G441 | date = March 2015 | pmid = 25540231 | pmc = 4346753 | doi = 10.1152/ajpgi.00328.2014 }}</ref>
Chronic inflammatory conditions of the biliary tract, including Primary Sclerosing Cholangitis (PSC) and Primary Biliary Cirrhosis (PBC), can lead to hardening of the ducts in the biliary tree.<ref>{{Cite journal |last1=Franco |first1=J. |last2=Saeian |first2=K. |date=April 1999 |title=Biliary tract inflammatory disorders: primary sclerosing cholangitis and primary biliary cirrhosis |journal=Current Gastroenterology Reports |volume=1 |issue=2 |pages=95–101 |doi=10.1007/s11894-996-0006-8 |issn=1522-8037 |pmid=10980934}}</ref>
An obstruction of the biliary tract can result in [[jaundice]], a yellowing of the skin and whites of the eyes.<ref name="urlDefinition: biliary tract from Online Medical Dictionary">{{cite web |url= http://cancerweb.ncl.ac.uk/cgi-bin/omd?biliary+tract |title=Definition: biliary tract | work = Online Medical Dictionary }}</ref>
== References == {{Reflist}}
{{Accessory digestive glands}} {{Authority control}}
{{DEFAULTSORT:Hepatobiliary System}} [[Category:Hepatology]]