Fig. 1. Mammalian and teleost liver architecture. (A) Schematic representation of the mammalian liver lobule. Portal tracts (white circles) surround bilayered hepatocyte plates (h). Each portal tract contains a portal vein radicle (pv), a hepatic artery radicle (ha), and 1 or 2 interlobular bile ducts (b). Apical bicellular canaliculi (c) are located between adjacent hepatocytes. Fenestrated sinusoidal endothelial cells that line the basal hepatocyte membrane (depicted in blue) allow uptake and transport of proteins and other macromolecules. Blood enters the liver lobule through pv and ha radicles, and flows through sinusoidal channels lined by basal endothelial cells towards the central vein (cv), the proximal branch of the hepatic venous system. (B) Schematic representation of the teleost tubular liver. Portal vein radicles (pv), hepatic artery radicles (ha) and bile ducts are not grouped together in portal tracts. Note, portal venous and hepatic venous (cv) radicles are indistinguishable, although they are depicted in different colors for this schematic. Hepatocytes are arranged in tubules rather than in bilayered plates, and are surrounded by fenestrated endothelia. Longitudinal, transverse and oblique sections of hepatocyte tubules are present in histological sections, but are often difficult to appreciate. Small bile ducts (ducts) reside within hepatocyte tubules. In this schematic, a bile duct composed of a single biliary epithelial cell (dc) anastomoses with three hepatocyte canaliculi (c). Unicellular canaliculi of cyprinid fish are tubular invaginations of the hepatocyte membrane that extend to a perinuclear location. Note, biliary-arteriolar tracts (not shown) are described for some fish. [Adapted from Hinton and Couch (Hinton and Couch, 1998).]