[Structure and function of lymphatic capillaries in synovial joint]

The review article focuses on the structure and function of lymphatic capillaries in connective tissues of skin, muscles and synovial membrane. Lymphatic capillaries (initial lymphatics) are formed from endothelial cells mutually arranged so that their intercellular junctions have different structure. In one of the different types of intercellular junctions the distal ends of endothelial cells overlap one another in the form of projections. Desmosomes are missing between the cell membranes of the internal and external projection without presence of any other junctional complexes. The external projection of the endothelial cell is tightly attached to the surrounding connective tissue with the help of anchoring filaments. The internal projection of the neighbouring endothelial cell may tilt over to the lumen of the lymphatic capillary and this may result in a several micrometers wide communication between the interstitium and the lumen with efflux of tissue fluid and leukocytes from the interstitium in to the lumen of the capillary. Lymphologists call the above mentioned openable intercellular junctions in their works also endothelial microvalves or primary valves. These primary valves in cooperation with classical (secondary) intralymphatic valves enable one way lymph flow during spontaneous contractions of the initial lymphatics. It is supposed that primary valves in lymphatic capillaries have an important role in the drainage of the connective tissues affected by inflammation also in the synovial joint.