Collagen fiber arrangement in canine hepatic venules

Cell-maceration/scanning electron microscopy, serial sections and scanning electron microscopy of vascular resin casts were employed to demonstrate th e arrangement of collagen fibers in the terminal hepatic venules, involving the central, intercalated and collecting veins in dog liver. In cell-macer ation specimens, each collagen fiber was observed to run in various directi ons, forming a sheath with a compact meshwork of collagen fibers. The colla genous meshwork in the hepatic venules was looser than those of the termina l portal venules and hepatic arterioles. Some collagen fibers formed bundle s with an elongated spiral arrangement encircling the wall of the terminal hepatic venules. In resin casts, these venules were observed as a twisted c onfiguration caused by spiral collagen bundles. A helical modification of s uch connective tissue bundles might provide a mechanically stable vascular structure and permit reversible changes in linear and circumferential vascu lar dimensions at the terminal tributaries of veins. Round or oval pores wi th diameters of approximately 9 mu m were also observed in the sheath of co llagen fibers. These pores, together with the relatively loose collagenous meshwork in the hepatic venules, might play a role in lymphocyte migration from these venules into the surrounding tissue and provide high permeabilit y to the venule walls. No such helical configuration and pores were observe d in either the portal venules or the hepatic arterioles.