Structure of lymphatic valves in the spinotrapezius muscle of the rat.

Lymphatic valves assure the forward propulsion of fluid along the lymphatic vessels. A description of valve function in skeletal muscle must be based on a knowledge of the valve morphology. To this end, histological sections of valves from lymphatic microvessels of the rat spinotrapezius muscle were examined with light microscopy. All of the approximately 50 valves studied from 20 rats had a bileaflet structure, with a buttress formed at each side of the valve by the fusion of opposing leaflets. This valve structure would allow the valve to close without inversion. There is no evidence for active smooth muscle action to open and close the valve. Since the Reynolds number of lymph flow is very small (about 0.0025), only pressure and viscous forces are available for valve closure. A particular mechanism based on the actual lymphatic valve structure is proposed.