The differential process of the epithelial cilia of the tracheal mucosa has occasionally been studied. However, the differential process of the whole mucous epithelium has scarcely been studied from an ultra-morphological point of view.
In this study, the differential process of the epithelia of the nasal and respiratory mucosae in rats was analyzed serially. In addition, the growth of the epithelium of the nasal mucosa in human embryos was studied, using a scanning electron microscope (SEM) and a transmission electron microscope (TEM).
Experimental results
A. Rats
(a) Nasal respiratory epithelium
(1) Primary cilia were observed in a few embryonic cells at the 13 th day of gestation. The number of cells having primary cilia increased in accordance with the number of days of gestation.
(2) In embryos at the 15 th day of gestation, cells having approximately 10 processes with a thickness between microvilli and cilia and with the same length as primary cilia were observed.
(3) Embryonic cells at the 16 th day of gestation were characterized by typical ciliated epithelium: cells having primary cilia disappeared and ciliated cells and secretory cells appeared. The lamina propriae were found to consist of a ciliated structure, collagen fibers, and elastic fibers.
(b) Tracheal mucous epithelium
(1) A few embryonic cells at the 14 th day of gestation had primary cilia. The number of ciliated cells was less than that in nasal respiratory epithelium.
(2) Ciliated cells were not observed in embryos at the 16 th day of gestation. The number of cells having primary cilia increased in comparison with the number of cells at the 14 th day or 15 th day of gestation.
(3) In embryos at the 17 th day of gestation, a few ciliated cells appeared first.
B. Epithelium of the inferior nasal concha of human fetuses
(1) Cells having primary cilia were observed in embryos at the 11 th week of gestation.
(2) In embryos at the 13 th week of gestation, ciliated cells appeared and increased in accordance with the number of days of gestation.
(3) In embryos at the 18 th week of gestation, secretory cells appeared. In embryos at the 27 th week of gestation, the release of secretory granules was evident.
(4) Non-ciliated cells decreased in accordance with the number of days of gestation.
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