The unit-concept of hepatic parenchyma--a re-examination based on angioarchitectural studies

The unit-character of the classical lobule (CL), mirrored essentially in the mode of both lobular aggregation and intralobular polarization, correlates with the angioarchitecture in the following way. (1) The portal venous tree can be divided into conducting and parenchymal portions. The conducting portion shows a remarkable variation in branch-length, diameter, and number of branching generations, whereas the parenchymal portion follows a strict scheme of branching, which terminates in spanning septum-like inflow-front. The latter is composed of unit areas, each of which, with a corresponding venous end, maintains a cone-shaped parenchymal mass (primary lobule or PL). Six to eight PLs make up one CL, whereby the inflow-fronts of the PLs are combined to form a closed surface covering the CL. (2) CLs, tightly packed together, constitute the parenchyma which is isotropic just with respect to this lobular aggregation. The interface between abutting CLs (inflow-front) forms a continuous system that extends throughout the liver, maintaining the uniformity of the lobular packing. (3) Sites of arterio-sinusoidal connection are always found within the portal inflow-zone where the architectural principle of stream-beds is determined by the mode of portal branching.