Normal respiratory epithelium

Note the pseudostratified ciliated epithelium with goblet cells. A blood vessel filled with RBC's is seen filling the bottom 25% of this slide.

This type of epithelium is seen in the upper respiratory tract and is gradually replaced by a simple, ciliated columnar epithelium with goblet cells in the bronchi. As the bronchi decrease in size the epithelium becomes cuboidal. In the bronchioles the goblet cells decrease in number and eventually disappear and the cilia are still present after all goblet cells have gone. The epithelium in the terminal and respiratory bronchioles becomes lower and lower and is flattened in the alveolar ducts and alveoli.