Light and electron microscopy of the structural organization of the tissue-lymphatic fluid drainage system in the mesentery: an experimental study.

Supplementing vital microscopy and histophysiology, we examined using combined light and electron microscopy the tissue fluid-lymphatic drainage system of the mesentery isolated from guinea pigs, rabbits, and tree shrews. In silver impregnated tissue, different types of lymphatics and blood vessels were able to be distinguished along with argyrophilic and argyrophobic structures in the connective tissue. Some initial lymphatic pathways were interrupted by non-endothelialized tissue zones thus forming separate but discrete vascular "islands". After carbon labeling of the lymphatic collectors, carbon particles were seen to escape from the initial lymphatic lumen at various sites. Electron microscopy revealed wide apertures in the lymphatic endothelial cells of these microvessels. These morphological findings support the concept of an "open" prelymphatic-lymphatic system in the mesentery. The special histometrical features exhibited by a flat membranous organ like the mesentery are discussed in terms of physiologic function of mesenteric tissue fluid transport.