It is not present in the vocal cords of the larynx, or the oropharynx and laryngopharynx, where instead the epithelium is stratified squamous.

[3] It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by the secretion of mucus and the action of mucociliary clearance.

The direction of their beat is targeted towards the pharynx, either upwards from the lower respiratory tract or downwards from the nasal structures.

[12] Goblet cells, so named because they are shaped like a wine goblet, are columnar epithelial cells that contain membrane-bound mucous granules and secrete mucus as part of the airway surface liquid (ASL), also known as the epithelial lining fluid, the composition of which is tightly regulated; the mucus helps maintain epithelial moisture and traps particulate material and pathogens moving through the airway.

[citation needed] The respiratory epithelium has a further role of immunity for the lungs - that of glucose homeostasis.

[16] The tight junctions act as a barrier that restricts the passage of glucose across the epithelium into the airway lumen.

[17] However, airway inflammation decreases the effectiveness of the tight junctions making the barrier more permeable to glucose.

[16] Increased levels of glucose in the airway surface liquid is associated with respiratory diseases, and hyperglycemia.