The ultrastructure of lymphatic valves in rabbits and mice

Abstract

The ultrastructure of lymphatic valves was studied in rabbits and mice. The lymphatic valves usually consist of two cusps but three or four are sometimes present. The cusps are covered by endothelium. Along the free edge of the cusps are endothelial cells which can differentiate morphologically from other endothelial cells. They are named "tip-cells"; they have pseudopodlike projections and abundant cytoplasmic filaments 60-90 A in diameter. Vesicles occur in endothelial cells of both lymphatic vessels and their valves; they are on the luminal or connective tissue side and are never provided with a diaphragm like that frequently observed in blood vessels. Joining endothelial cells are zonulae occludentes but desmosomes are not observed. No open intercellular junctions are encountered along the valvular endothelium. A basement membrane (basal lamina) is more frequently observed in valves than in walls of lymphatic vessels. Connective tissue in the cusps consists of collagenous fibrils, fine filaments and fibroblasts.

Structure of Lymphatic Valves in the Spinotrapezius Muscle of the Rat

“…The importance of the lymphatic valves is that they prevent retro grade flow. The lymphatic valve morphology determined here for the spinotrapezius mus cle is similar to that found in larger lym phatic vessels of other species [Albertine et al, 1982;Kampmcier, 1928;Takada, 1971;Vajda and Tomcsik. 1971], We have consis tently found a bileaflct structure with a lin ing of highly attenuated endothelium.…”

“…The structure of the lymphatic valves has been described for the larger col lecting lymphatics of human fetuses [Kampmeier, 1928], dogs [Albertine et al, 1982], cats [Vajda and Tomcsik, 1971], and rabbits and mice [Takada, 1971], The lymphatic valves observed were predominantly bicus pid, but monocuspid and tricuspid valves have also been described. There is no de tailed information concerning morphologi cal and functional characteristics of the lym phatic valves in skeletal muscle.…”

Passive Pressure–Diameter Relationship and Structural Composition of Rat Mesenteric Lymphangions

“…Vajda et al 8 and Gnepp et al 9 claimed to detect elastin in the lymphatic valves; however, other studies reported only an endothelial layer on the valve leaflets and no elastin. 22,23 Skalak et al 3 showed that lymphatic valves in the spinotrapezius muscle of the rat had collagen on both sides, along with endothelial cells. Albertine et al 24 observed only collagen fibrils and fibroblasts in canine lymphatic valves.…”

Contractile Physiology of Lymphatics

“…[24][25][26][27][28][29][30][31] These important structures are a hallmark of the lymphatic network and their proper function depends upon some unique properties of the lymphatic. 24,26,29,30,32,33 The function of the lymphatic valves is thought to be driven by the pressures and flow of fluid across them, given their unique structure. …”