Fig. 2.

The biliary system of the liver. (A) Schematic depiction of the extra- and intra-hepatic bile duct systems and links to the gall bladder. (B) The hexagonal lobular structure of the liver, with a central vein (CV) surrounded by six portal veins (PV), each paired with a bile duct and hepatic artery, a trio known as the portal triad, enlarged in (C). These three structures are embedded in portal vein mesenchyme, which also contains a lymphatic system.Blood flows centripetally from the portal veins and hepatic arteries to the central vein, along sinusoids lined by liver sinusoidal endothelial cells (LSECs), Kupffer cells and hepatic stellate cells (HSCs).Bile flows instead along bile canaliculi formed by hepatocytes, towards the canals of Hering and into the bile ducts. (D) Bile ducts are highly polarized structures, with an apical cilium (not pictured) and apicobasal distribution of channels and receptors, including anion exchange protein 2 (AE2), aquaporin 1 and 4 (AQP1, AQP4), the cystic fibrosis transmembrane receptor (CFTR) and the secretin receptor.