The biliary tree is composed of two parts - the intrahepatic biliary tree and the extrahepatic biliary tree. The ducts that are found inside the liver are called the intrahepatic ducts, while the ducts located outside the liver are known as the extrahepatic ducts.

Intrahepatic biliary tree

The intrahepatic biliary tree is formed by bile canaliculi, canals of Hering, bile ductules and various ducts surrounded by hepatic and connective tissue cells.

The bile canaliculus (bile capillary) is the smallest unit of the intrahepatic biliary tree and, overall, the biliary system. It is a thin tube that is surrounded by hepatocytes. The bile canaliculus receives and collects hepatocyte-secreted bile.

The canal of Hering is a larger intrahepatic bile ductule surrounded by three types of cells - hepatocytes, cholangiocytes and hepatic progenitor (stem) cells. In contrast, the bile ductules are intrahepatic bile tubes that are lined only by the cholangiocytes.

Further, various bile ductules unite and form the interlobular bile ducts, and then these merge into area bile ducts. All ductules and ducts smaller than area bile ducts are considered small bile ducts, while all tubes larger than area bile ducts are classified as large bile ducts.

The area bile ducts further form segmental bile ducts. The segmental ducts combine to form sectoral ducts. And finally, sectoral bile ducts fuse and create the right and left hepatic ducts.

Left and right hepatic ducts

The left hepatic duct is formed by the union of the ducts from liver segments 2 and 3. The left hepatic duct is located next to the umbilical part of the left portal vein. Segments 4 and 1 are drained by additional ducts flowing into the left hepatic duct.

The right hepatic duct is formed by merging the right anterior (medial) and right posterior (lateral) sectoral ducts:

Note: This pattern we describe is considered typical and is found in more than half of the world’s population. However, some anatomical variations may be present. About 10 - 15% of people do not have the right hepatic duct. Also, some people show trifurcation patterns. In this case, three ducts - the right anterior (medial) sectoral, right posterior (lateral) sectoral and left hepatic ducts - join together and form the common hepatic duct. In another 10 - 15% of cases, one of the right sectoral ducts (typically the right posterior (lateral) sectoral) merges with the left hepatic duct.

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Intrahepatic biliary tree