FUNCTIONAL-ANATOMY OF HUMAN LACRIMAL DUCT EPITHELIUM

Resorption of tear fluid in the lacrimal ducts has hitherto been contr oversial; one reason for this has been insufficient knowledge of the a natomical structure and function of the lacrimal duct epithelium. The present study analyzes the structure of lacrimal duct epithelium by me ans of histological, histochemical, immunohistochemical and electronmi croscopical methods and draws a conclusion about its physiological fun ction regarding its role in immunodeficiency. Investigations were per formed on 31 lacrimal systems of 17 male and 14 female individuals (ag ed 54-88 years). Lacrimal ducts are surrounded by a wide-ranging caver nous system, which is embedded in an osseous canal between the maxilla and the lacrimal bone. The internal wall of the lacrimal canaliculi i s lined by a stratified epithelium. The lacrimal sac and nasolacrimal duct contain a double-layered epithelium, which rests on a broad basem ent membrane. In their epical part epithelial cells contain large lipi d droplets and secretory vacuoles. Epithelial cells are faced by micro villi and some tufts of kinociliae are also visible. Goblet cells are integrated in the epithelium as solitary cells or in a characteristica l arrangement of several cells. The secretory product of these cells c ontains carbohydrates including fucose and sialic acid. Inside the sur rounding cavernous system serous glands are found that open their excr etory ducts into the lacrimal sac and nasolacrimal duct. Some T- and B -lymphocytes and macrophages may be demonstrated immunohistochemically in the submucosa partly penetrating the epithelium. Synthesized mucin s of goblet cells form a specialized protective layer on the epitheliu m of the lacrimal ducts, which functionally serves for a simplified dr ainage of tear fluid into the inferior meatus of the nose. Together wi th immunocompetent cells, the protective layer plays a role in antigen defense and prevents invasion of pathogenic agents. The facing of epi thelial cells by microvilli gives hints of reabsorption of lacrimal fl uid inside the lacrimal ducts.