The cervical lymphatic ducts of the dog: Structure and function of the endothelial lining

Abstract

In addition to the usual organelles, the endothelial cells of the cervical lymphatic ducts contain numerous fine filaments throughout the central portion of their cytoplasm. The histochemical localization of a myoid fibril stain within the endothelial cells suggests that these filaments are myofilaments which might make the cell capable of some degree of contraction. Fine “anchoring filaments” previously described by others in lymphatic capillaries are observed beneath the endothelium of the cervical collecting ducts. There are two kinds of filament: small filaments and larger filaments that resemble tubules. The abluminal surfaces of the endothelial cells are marked by depressions which could be either pockets or grooves. These depressions are formed by processes of adjacent endothelial cells at some of their junctions and are populated by numerous tubular filaments which have been renamed “junctional filaments.” Although these ducts are among the larger lymph ducts of the dog's body, the smooth muscle cell component is sparse. The paucity of contractile cells and the complete absence of grossly observable spontaneous contractions would indicate that in the cervical ducts of the dog instrinsic lymphatic contraction is not a prime mechanism in the propulsion of lymph. The endothelial lining with its specialized junctions, anchoring filaments and possible presence of myofilaments may, however, play a role in the regulation of lymph flow in this otherwise passive system.