The vascular anatomy of the liver of the monitor lizard (Genus varanus).

Abstract

AbstractThe gross and microscopic anatomy of the vasculature of the monitor lizard liver was studied. The portal vein has a peculiar arrangement of smooth muscle. The tunical media of the entering portal vein has bundles of smooth muscle cells separated by large numbers of collagenous fibers. The amount of smooth muscle decreases as the vessel decreases in diameter and soon one finds intermittent broad, thin bands of smooth muscle. As the caliber of the vessels continues to decrease, the smooth muscle bands become narrower and thicker so that they appear as doughnut‐shaped sphincters. The sphincters are usually found at the beginning of each branch of the portal vein as well as along the course of veins between areas of branching. Some sphincters are found in direct contact with the outer capsule of the liver. Sphincters occur in the terminal branches of the portal vein just proximal to the sinusoids.Small numbers of scattered smooth muscle cells were seen arranged longitudinally, obliquely, or circularly in the smaller hepatic veins. Even the large hepatic veins had only small amounts of smooth muscle. At no place along the course of hepatic veins could smooth muscle sphincters equivalent to those seen around portal veins be found.The monitor lizard should be an excellent subject for physiological and pharmacological studies of regulation of intrahepatic portal vein blood flow.