A STUDY OF THE 3-DIMENSIONAL ORGANIZATION OF THE HUMAN DIAPHRAGMATIC LYMPHATIC LACUNAE AND LYMPHATIC DRAINAGE UNITS

The peritoneal stomata, lymphatic drainage units and subperitoneal ter minal lymphatics, called lymphatic lacunae, form a specialized drainag e system in the diaphragm, by which absorption of fluid in bulk, parti cles and cells is carried out in the peritoneal cavity. The aim of thi s study is to elucidate the three-dimensional organization and functio n of the subperitoneal lymphatic lacunae and lymphatic drainage units by using lymphatic casts in the scanning electron microscope (SEM), OD O (OsO4 - DMSO - OsO4) freeze fracture, conventional SEM and the trans mission electron microscope (TEM). The subperitoneal lymphatic lacuna is unique for its large size and its multiple morphology and can be re cognized by its broad, flattened enlargement and the blind-ends of lym phatic vessels, from which extend numerous main lymphatic vessels and side branches. These lymphatic vessels communicate with each other and form a rich lymphatic plexus under the diaphragmatic peritoneum. Two layers of lymphatic networks, i.e. the subperitoneal plexus and the de eper plexus are found in the muscular portion. Only one layer is prese nt in the tendinous portion of the human diaphragm. The lymphatic plex us is denser in the tendinous portion than that in the muscular portio n. The lymphatic lacunae occur exclusively in the muscular portion of the human diaphragm. The lumina of lymphatic lacunae are separated fro m the peritoneal cavity by a barrier consisting of cuboidal mesothelia l cells, endothelial cells of the lymphatic lacunae and intervening co nnective tissue forming a lymphatic drainage unit. All these three com ponents of the lymphatic drainage unit abut upon each other, but are n ot linked by specialized junctions. The cuboidal mesothelial cells fre quently extend valve-like cytoplasmic processes that bridge the subper itoneal channel and make give it a tortuous course. The fibrous layer of the connective tissue is arranged in fiber bundles and gives a thre e-dimensional network forming the floor of the peritoneal stomata and the roof of the lymphatic lacunae. Via the fibrous network, the cuboid al mesothelial cells and the endothelial cells of the lacunae come int o close contact with each other and form short subperitoneal channels which connect the peritoneal cavity with the subperitoneal lymphatic l acunae. The lymphatic drainage units may regulate the material absorpt ion of the peritoneal stomata from the peritoneal cavity. It is sugges ted that the peritoneal stomata together with the subperitoneal channe ls, lymphatic drainage units and lymphatic lacunae comprise an importa nt diaphragmatic lymphatic drainage system which plays an important ro le in the absorption of materials from the peritoneal cavity.