Development of the ciliary epithelium in human nose.

In 15 foetuses, ranging in age from the 8th to the 23rd menstrual week, the development of ciliated cells in the nose was analysed quantitatively by counting ciliated cells in high power fields. The formation of ciliated cells is the first step in the differentiation from embryonic to respiratory epithelium, which starts in the 9th menstrual week. The density of ciliated cells increases strongly and reaches a maximum already in the 16th week. It does not further increase in older foetuses and prematures. Based on the rapid increase in density it is assumed that the differentiation of ciliated cells takes about 2-3 days which is considerably shorter than for goblet cells.