Biliary tract

Biliary tract
	Ducts of the biliary tract
Details
Function	Facilitate movement of bile, which aids in fat absorption
Identifiers
MeSH	D001659
	Anatomical terminology

The biliary tract, (biliary tree or biliary system) refers to the liver, gall bladder and bile ducts, and how they work together to make, store and secrete bile. Bile consists of water, electrolytes, bile acids, cholesterol, phospholipids and conjugated bilirubin. Some components are synthesised by hepatocytes (liver cells), the rest are extracted from the blood by the liver.

Bile is secreted by the liver into small ducts that join to form the common hepatic duct. Between meals, secreted bile is stored in the gall bladder. During a meal, the bile is secreted into the duodenum to rid the body of waste stored in the bile as well as aid in the absorption of dietary fats and oils.

Structure

1. Bile ducts: 2. Intrahepatic bile ducts, 3. Left and right hepatic ducts, 4. Common hepatic duct, 5. Cystic duct, 6. Common bile duct, 7. Ampulla of Vater, 8. Major duodenal papilla
9. Gallbladder, 10–11. Right and left lobes of liver. 12. Spleen.
13. Esophagus. 14. Stomach. 15. Pancreas: 16. Accessory pancreatic duct, 17. Pancreatic duct.
18. Small intestine: 19. Duodenum, 20. Jejunum
21–22. Right and left kidneys.
The front border of the liver has been lifted up (brown arrow).[1]

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 hepatic artery, and the portal vein form the central axis of the portal triad. Bile flows in the direction opposite to that of the blood present in the other two channels.

The system is usually referred to as the biliary tract or system, [2]and can include the use of the term "hepatobiliary" when used to refer just to the liver and bile ducts.[3] 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.[4]

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 >>
These merge to form the common hepatic duct
This exits the liver and joins with the cystic duct from gall bladder
Together these form the common bile duct which joins the pancreatic duct
These pass through the ampulla of Vater and enter the duodenum

Function

Bile is secreted by the liver into small ducts that join to form the common hepatic duct. 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. During a meal, the smooth muscles in the gallbladder wall contract, leading to the bile being secreted into the duodenum to rid the body of waste stored in the bile as well as aid in the absorption of dietary fats and oils by solubilizing them using bile acids.

Clinical significance

Pressure inside in the biliary tree can give rise to gallstones and lead to cirrhosis of the liver.

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 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 obstructions.

An obstruction of the biliary tract can result in jaundice, a yellowing of the skin and whites of the eyes. [5]

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References

Standring S, Borley NR, eds. (2008). Gray's anatomy : the anatomical basis of clinical practice. Brown JL, Moore LA (40th ed.). London: Churchill Livingstone. pp. 1163, 1177, 1185–6. ISBN 978-0-8089-2371-8.
Biliary+tract at the US National Library of Medicine Medical Subject Headings (MeSH)
Dorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 846. ISBN 978-1-4160-6257-8.
Dorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 1946. ISBN 978-1-4160-6257-8.
"Definition: biliary tract from Online Medical Dictionary".

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[1] Standring S, Borley NR, eds. (2008). Gray's anatomy : the anatomical basis of clinical practice. Brown JL, Moore LA (40th ed.). London: Churchill Livingstone. pp. 1163, 1177, 1185–6. ISBN 978-0-8089-2371-8.

[2] Biliary+tract at the US National Library of Medicine Medical Subject Headings (MeSH)

[3] Dorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 846. ISBN 978-1-4160-6257-8.

[4] Dorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 1946. ISBN 978-1-4160-6257-8.

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