Abstract
To elucidate the ultrastructural organization of the tracheal epithelium and especially the fine structure of the non-ciliated cells (brush cells), the electron microscope observations were carried out. Many rats in the postnatal developmental stages and adult ones were used in this study. The tracheal epithelium of the rats is composed of a simple columnar or a pseudostratified ciliated epithelium, and it contains four distinct types of cells; ciliated cells, mucous cells (goblet cells), basal cells, and non-ciliated cells (brush cells). The ciliated cell has a clear cytoplasm compared with those of the other types of cells and favorable amount of cell organelles. Sometimes, the process of the ciliogenesis can be sproradically seen in the presumably ciliated cells early in the postnatal developmental stages and also in the adult ones. The mucous secretory cells with a fairly dense cytoplasm provided with plenty of rER and other cell organelles are more predominant in number in immature rats. However, there are scarcely seen the mucous cells provided with a typical goblet composed of many secretory granules in the apical cytoplasm. Non-ciliated cells aligned the luminal surface of the tracheal epithelium are divided into two categories, one is the mucous secretory cell and the other is the so-called brush cell provided with the brush border on its luminal surface, and the latter also contains many characteristic granules of small size. Some of these granules contain a dense spherical core, and frequently situate in the basal part or along the lateral cell boundary clustered in small groups. On the other hand, there are frequently observed many naked nerve endings, and most of them contain both small clear vesicles and large cored vesicles, and others contain also small granular vesicles, neurotubules, small mitochondria or scarce glycogen particles. However, no epithelioneural junctions can be discerned between the brush cells and the nerve endings in the epithelium. These findings mentioned above may be probably assumed that the brush cell plays a role of an endocrine function to secret the containing granules into the connective tissue of the tracheal mucous membrance in rats.
