Electron Microscopic Study on Differentiation of Tracheal Epithelium in Human Fetus

Lee, Sang Yong; Nam, Kwang Il; Park, Sung Sik; Lee, Sang Yong; Nam, Kwang Il; Park, Sung Sik

Abstract

The human trachea is normally lined by a pseudostratified ciliated columnar epithelium where ciliated, goblet, intermediate and basal cells are mainly represented. However the fetal tracheal epithelium was found to be composed of ciliated, non-ciliated and basal cells. The present study was designed to characterize the development of ciliated cells in the fetal trachea at mid (19 weeks) and last (32 weeks) trimester of gestation. At 19 weeks of gestation, the tracheal epithelium, 35 µm in height, was composed of surface, intermediate and basal layers. The surface cells were subdivided into ciliated, immature ciliated, non-ciliated, granule containing and goblet cells. The ciliated cells covered approximately half of the luminal surface area. The immature ciliated cells contained basal bodies, but the apical membrane was not invested with cilia. The granule containing cells contained numerous dense granules, 0.3-0.7 µm in diameter, in the apical cytoplasm. The goblet cells contained less electron dense granules, 1-2 µm in diameter, in the apical cytoplasm. The cells in intermediate layer were relatively undifferentiated and contained poorly developed organelles. Submucosal gland were well differentiated and were composed of the mucous and serous cells. At 32 weeks of gestation, the tracheal epithelium, 50µm in height, was also composed of surface, intermediate and basal layer. The surface cells were composed of ciliated, non-ciliated and goblet cells. The ciliated cells, dominant type of surface cells, were subdivided into mitochondria-rich cells (type I) and smooth endoplasmic reticulum-rich cells (type II). The non-ciliated cell were of three subtypes : mitochondria-rich cells (type A), glycogen and microfilament-containing cells (type B) and cells with bulging apical surface into the lumen (type C). Small granule containing cell appeared in the basal layer. These cells contained clear vesicles, 50 ãŽšm in diameter, and dense granules, 100-300 ãŽšm in diameter. Submucosal gland were well developed and consisting of mucous, serous and myoepithelial cells. These results indicate that the cell populations of the tracheal epithelium at late stage of pregnancy have essential features similar to those of adult. and show that the different steps of ciliogenesis could be identified.