Patterns of cilia formation in the lower respiratory tract of the dog: a scanning electron microscopic study

A scanning electron microscopic study of the distribution of ciliated cells in the tracheobronchial tree of 25 dogs whose ages ranged from four hours to six months was carried out. In newborn puppies, only the dorsal wall of the trachea was completely ciliated while the lateral and ventral walls showed patchy ciliation. This pattern of cilia formation persisted until five days of age when the whole tracheal wall was found to be completely ciliated. The bronchus of newborn puppies was uniformly poorly ciliated but almost complete ciliation was achieved by two days. Likewise, large and small bronchioles of newborn animals had few cilia and, although the number of ciliated cells had increased by two days, complete ciliation was never observed regardless of the age of the dog. No ciliated cells were found in the respiratory bronchioles of any of the 25 dogs.