Scanning electron microscopy of an elastic fiber network which forms the internal elastic lamina in canine saphenous...

Scanning electron microscopy (SEM) was used to study the arrangement of elastic fibers in the canine saphenous vein as the basis for further studies of veins used in by-pass grafting operations. The elastic fiber arrangement in distended and non-distended veins was examined in both immersion-fixed and perfusion-fixed vessels. Transmission electron microscope (TEM) observation of the SEM samples confirmed the identity of these fibrillar structures as elastic fibers. In addition, specific stains for elastic fibers (Verhoeff's iron hematoxylin and orcein) were used. The elastic fibers forming the internal elastic lamina were arranged in a fishnet-like pattern. Large-diameter fibers, running longitudinally along the vascular wall, were interconnected by smaller oblique fibers. Together the fibers formed an elastic cylindrical network between the endothelium and the smooth muscle cells. The thicker longitudinal fibers were the same diameter in distended and non-distended veins. By contrast, the oblique fibers were thinner and more complexly branched in distended veins. The architecture of the elastic fiber network contributes to vascular flexibility and allows circumferential distension. The interconnecting oblique fibers presumably serve to distribute internal pressure equally around the venous wall.