Ciliogenesis and ciliation of the respiratory epithelium in the human fetal cartilaginous trachea.

Ciliogenesis of the respiratory epithelium in the human cartilaginous trachea start during the 12th week of gestation. Ciliary shafts are first seen under the scanning electron microscope during the 13th week. Unlike its membranous counterpart, ciliary shafts appear all over the epithelial surface at almost the same time. Epithelial cells destined to become ciliated cells first develop numerous long and thin microvilli. A process of individual cell extrusion and proliferation of neuroepithelial bodies around the carinal angle precede ciliation in the respiratory epithelium of the cartilaginous trachea. Epithelial cell differentiation patterns in both the cartilaginous and membranous trachea are different. The mechanisms involved in modulating cell differentiation are currently under investigation.