Functional anatomy of the retro- and suprahepatic portions of the human inferior vena cava and their main affluents.

The arrangement of muscle, collagen and elastic fibers was studied in the retro- and suprahepatic (subdiaphragmatic) portions of the inferior vena cava, the hepatic veins and their main affluents. Distinctive features of the longitudinal and transverse muscle bundles are described. In these portions of the vena cava, both bundle systems are clearly separate and any continuity was observed only at the entrances of the hepatic veins. A musculo-venulolymphatic complex was noted in spurs formed by the vascular junctions. The hepatic veins and their main affluents exhibit an elliptical contour in transverse section, which apparently results from cranial and caudal thickenings of the longitudinal muscle layer. Many of these bundles are in continuity with those of the transverse muscle layer. Terminal elastic tendons were rarely observed in connection with muscle fibers of the inferior vena cava and are not present in the hepatic veins and their main affluents. In terms of form and function, the relatively thin muscular layer has a dilating action on the hepatic venous system because of the external fixed insertion point of the muscle bundles. Such an arrangement and a "polar" disposition of the muscle bundles in the hepatic venous system may assists in "suction" of the blood toward the heart. A sphincteric control of the ostia by means of crossed muscular loops supported by venulo-lymphatic micropads is a possibility.