Ultrastructure of rat tracheal epithelium

The appearance in freeze-fracture replicas of the various cells comprising the tracheal epithelium was correlated with their structure as revealed by scanning electron microscopy and by transmission electron microscopy of thin sections. Ciliated cells can be recognized by characteristic images of axonemal plasma membrane and, in oblique planes of fracture, by microtubular arrays in axonemes and basal bodies. Secretory granules and organelles associated with secretory function permit identification of mucous cells. Microvilli, desmosomes, and the apical cytocavitary network of brush cells form distinctive images. The triangular shape, desmosomes, and relationship to fibrillar connective tissues are features of basal cells which are useful for recognition of replicas of those cells. Freeze fracture allows detailed description of plasma membrane structure. Leaky tight junctions are present between the several types of surface cells, and there are small gap junctions in which mucous cells and basal cells participate.