New structural details of dermal lymphatic valves and its functional interpretation.

Dermal lymphatics (rat and human) were studied electronmicroscopically and changes within the lymphatic wall including neoformation of intralymphatic valves were followed by serial sections. Two new forms of intralymphatic valves were observed-unicellular valve or single endothelial cell extension deep into the lymphatic lumen and bunch valve, or a connective tissue core with numerous tip-cells at its cuspidal edge. These structures functioned as "flap" or "helper" valves and like inlet (intramural) valves, they were variable structures appearing and disappearing with changes in the local interstitial environment. Lymphatic capillaries probably act as microscopic pistons to pump and suction lymph fluid in a centripetal direction.