Pseudostratified epithelium is a type of epithelium that appears to be stratified but instead consists of a single layer of irregularly shaped and differently sized columnar cells. The nuclei of neighboring cells appear at different levels rather than clustered in the basal end. They function to excrete mucous to serve as a lubricant. Ciliated pseudostratified columnar epithelium cells are found in places such as the trachea and upper respiratory tract, where their cilia and mucous secretions help collect foreign materials so you can cough or sneeze them out.