New observations on the fine structure of the normal nasopharyngeal epithelium of the mouse

The ciliated columnar epithelium in the mouse nasopharynx was studied by use of light and electron microscopes. The ciliated cells were divided into 3 types because of the variability in electron density of the ground cytoplasm. The dark ciliated cells were characterized by well-developed rough endoplasmic reticulum and rod-shaped mitochondria with regular arrangements of pronounced cristae. In the light ciliated cells endoplasmic reticulum was poorly developed and mitochondria were vacuolated with irregular arrangements of cristae. Furthermore, there existed the "medium ciliated cells," termed by the authors, of which the cytoplasm was medium in electron density between the dark and the light ciliated cells, and some mitochondria were rod-shaped and others were vacuolated. The medium ciliated cells are regarded to be at a stage of transformation from the dark ciliated cells to the light ones. These findings suggest that the dark ciliated cells swell to decrease their electron density with declining activity, and finally transform into the light ciliated cells. The cells, termed the "potential ciliated cells" by the authors, were scattered between the ciliated cells, reached the lumen and had no cilia. They contained many procentrioles suggesting ciliogenesis and had a cytoplasm of the same electron density as that of the dark ciliated cells. It is considered that the dark ciliated cells originate from the potential ciliated cells.