The terminal hepatic microcirculation in the rat.

The hepatic microcirculation was observed microscopically in the transilluminated liver of the rat. The portal and hepatic venous microvessels were classified into four orders according to their branching hierarchy, and the hepatic sinusoids into branching, direct and interconnecting types according to their topographic arrangements. The diameters of the various orders of microvessels and types of sinusoids were measured by serial photomicrography, and the velocity of the erythrocytes in these various microvessels and sinusoids by the dual-slit photometric technique. The microvascular volume flows were calculated from these data. In both portal and hepatic venous systems, the erythrocyte velocity and the volume flow significantly decreased in successive orders of the microvessels in apparent relation to the cross-sectional areas. The diameters of the three types of sinusoids did not significantly differ, but the velocity of the erythrocytes in the direct sinusoid was significantly faster than that in the branching sinusoid while that in the inter-connecting sinusoid fluctuated widely.