Respiratory epithelium

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Respiratory epithelium is another name for ciliated pseudostratified columnar epithelium with goblet cells. "Pseudostratified" refers to the histological appearance in which the nuclei are not aligned in the same plane and is really an artifact of sectioning and the irregular shape of the cells. An important point is that all cells make contact with the basement membrane and are in fact a single layer of cells--hence the "pseudo." Goblet cells are so-called because of their distinctive appearance on histology; they secrete mucus which keeps the epithelium moist and traps particulate material moving through the airway.

The cilia of the respiratory epithelium beat in a concerted effort to move mucus and trapped particles towards the oropharynx for expectoration or swallowing to the stomach where the acidic pH helps to neutralize any foreign material or micro-organisms.

Although the respiratory tract passes through and includes the oropharynx the swallowing of food exposes the epithelium to constant wear and tear. For this reason there is a transition zone superior to the larynx and caudal to the nasopharynx where the respiratory epithelium gives way to stratified squamous epithelium which is better suited to the constant sloughing and abrasion. The squamous layer of the oropharynx is continuous with the esophagus.

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