<ORIGINAL REPORT>THE ULTRASTRUCTURE OF THE CLARA CELL IN THE BRONCHIOLAR EPITHELIUM

Abstract

The terminal bronchiolar epithelium of the mouse and the guinea pig were examined with the scanning electron microscope and the conventional electron microscope. The ciliated cells and the Clara cells were well preserved and it is possible to discern individual cell with the scanning electron microscope. The apical part of the cytoplasm containing the agranular endoplasmic reticulum was occasionally seen to be extruded into the bronchiolar lumen. This finding indicated that the Clara cell has an apocrine secretory function. Osmiophilic lamellar inclusions are rarely found in this cell. However, there is no proof that they are the important source of the pulmonary surfactant.