Electron microscopic observation of ciliated cysts in the human oviduct epithelium

Intracytoplasmic ciliated cysts were observed in the human oviduct epithelium. Transmission electron microscopy demonstrated the occurrence and fine structure of those cysts, clarifying the process of their opening to the oviduct lumen. When located apically in the epithelial layer, the cysts moved upwards and expanded into the oviduct lumen, leaving a thin cytoplasmic layer, until they broke into the oviduct lumen. In contrast, basally-lying cysts did not move but were approached by an invagination of the epithelial surface which extended toward the cell base. The cysts were then broken onto the bottom of the invagination and consequently opened into the oviduct lumen. Although the intracytoplasmic ciliated cysts have previously been considered to be formed by abnormal ciliogenesis, the present study indicates that, at least in the human oviduct, they contribute to the formation of the normal ciliated border of the epithelium.