ORGANIZATION OF THE BLOOD AND LYMPHATIC MICROVASCULATURE OF THE GALLBLADDER IN THE GUINEA-PIG - A SCANNING ELECTRON-MICROSCOPIC STUDY

The organization of the blood and lymphatic microvessels of the gallbl adder in the guinea pig is demonstrated by scanning electron microscop y (SEM) of vascular corrosion casts, and SEM of KOH-macerated tissues. In the lamina propria of the gallbladder, there is a dense network of subepithelial capillaries. The network is supplied by the arterioles that come off the arterial plexus located deep in the lamina propria. The network gathers into the postcapillary venules continuous with the collecting venular plexus located immediately below the subepithelial capillary network. The precapillary arterioles are sparsely surrounde d by a single layer of circularly oriented extensions of smooth muscle cells. The terminal arterioles are endowed with circularly oriented f usiform smooth muscle cells. The nervous plexus is also noticed along the terminal arterioles. The capillaries are embraced by flat prolonga tions af pericytes. The postcapillary venules are sparsely surrounded by stellate pericytes and the collecting venules are sparsely surround ed by elongated or branched spindle-shaped, primitive smooth muscle ce lls which extend their long process in various directions along the va scular wall. The lymphatics are mostly located in the subserosal layer . The tips of the initial lymphatics are closed by endothelial cells, although there are frequently some gaps between them. The thin laps of the lymphatic endothelial cells overlap or interdigitate with each ot her. The luminar surfaces of the lymphatics show oval nuclear protrusi ons, while the abluminal surfaces showed numerous microfolds except fo r the oval and flat nuclear portions. The lymphatics possess neither s mooth muscle cells nor pericytes. (C) 1997 Wiley-Liss, Inc.