So far many kinds of light microscopic and electron microscopic studies of ciliated epithelium of various animals have been made, but researches on the human tracheal epithelium in the electron microscope are very few, and only one brief report of RHODIN (1959) is known to us. In the present study the materials were obtained from men of 45 and 54 years and women of 42 and 59 years on the opportunity of the operation of tracheotomy and laryngectomy. The materials were fixed in osmium tetroxide adjusted to pH 7.4 with veronal acetate buffer and embedded in styrene and n-butyl methacrylate or in epon. Thin sections were stained with uranyl acetate, and examined in the electron microscope at magnification of 1, 000-10, 000.
1. The structure of the ciliated cells of the human trachea is generally such as ever been written in other organs. Through careful observation, however, it has been confirmed that the limiting membrane of the cilia occasionally consists of two layers. In the cilia interior are seen 9 pairs of peripheral axial filaments and one pair of central axial filaments, the latter being enclosed by one-layer membrane. The basal corpuscle of the cilium is made up of fused peripheral axial filaments and its interior, the latter possessing a small round or egg-shaped shell. The root of the cilium from the ringshaped side wall of basal corpuscle shows a periodic structure with a period of 60mμ. In each period, i. e. between the two dense bands a thinner dense interband is found.
2. Generally microvilli develop well. They branch sometimes. Their tips often swell. Sometimes pinocytotic vesicles are seen in the microvilli. GOLGI apparatus is located on the upper side of the nucleus, and is composed of GOLGI membranes, vesicles and on some occasions vacuoles. Mitochondoria, which are round or bacilliform, sometimes branched, with cristae mitochodriales are disposed to gather under the cilia, but never touch their basal part. So-called‘hypobasale hyaline Zone’reported by HIOKI under the light microscope could not be confirmed in the present study. Occasions sometimes arise when the mitochondria are swollen and the cristae mitochondriales are dispersed, and small high electron dense granula occupy their interior. It is considered that it depends on the functional stages of the cell. Moreover many small vesicles are observed scatteringly in the cytoplasm and many multivesicular bodies are recognized above the nucleus.
3. Coarse granules of high electron density present in the cytoplasm and are classified into 2 kinds. 1. round or oval-formed comparatively clear granules with a limiting membrane and of high electron dense homogeneous ground substance. In the interior of this granule, high electron dense small granules of various size which are adjacent to the inside of the limiting membrane, are frequently observed. Probably electron density of the granule grows higher with the increase of the small granules in number. 2. round granules of concentric lamellar structure. They are seen numerous near the GOLGI apparatus. It is to be considered that some of the GOLGI vesicles gradually increase their electron density and at the same time show concentric lamellar structure in the interior, during which high electron dense substance deposits itself in the lamellar structure, and finally these granules change into a high electron dense granules without structure. But the reverse case may be taken into consideration with regard to the process of formation of the above mentioned granules. Furthermore, near the granules, rough surfaced endoplasmic reticula and RNA granules are seen. To what extent these bodies have to do with the process of granule formation is unknown.
4. There were findings which are in favour of HIOKI's ones under the light microscope concerning the transformation of the ciliated cell of the trachea to the goblet cell in man.
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