Scanning electron microscopic examinations of microvascular casts of the rat liver and bile duct.

Microvascular features of normal rat livers and bile duct system were examined with the vascular casts using methacrylated resin. Portal vein branches not only showed regular tapered down bifurcations but also had many side branches, some of which were directly connected with sinusoids. Terminations of hepatic arterial branches were divided into three types: 1) Many branches pouring into peribiliary capillary plexus (PBP), 2) branches directly pouring into periportal sinusoids and/or peripheral portal vein branches via arterio-portal anastomoses, and 3) anastomoses with periportal vascular plexus. PBP was composed of rich vascular networks. In large portal tracts, the plexus showed two layers, that is, the inner layer made up of a close network of capillary vessels and the outer layer consisting of a loose network of arteries and veins, while the PBP in the small portal tracts was composed of only a single layer of loose capillary network. Transitional features of these two patterns were found in the medium-sized portal tracts. PBP was supplied by afferent vessels from the interlobular hepatic artery as described above, and were directly connected with interlobular branches of the portal vein (internal root). The extrahepatic bile duct revealed a much richer vasculature than the intrahepatic bile duct. Both arterial and venous branches were ramified at almost right angle from a pair of arteries and veins running parallel with the bile duct. Occasional strictures, which might have been sphincter portions of the media, were noted at the branching sites of the artery.(ABSTRACT TRUNCATED AT 250 WORDS)