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The respiratory epithelium lining the upper respiratory airways is classified as ''ciliated pseudostratified columnar epithelium.''<ref>Mescher AL, "Chapter 17. The Respiratory System" (Chapter). Mescher AL: Junqueira's Basic Histology: Text & Atlas, 12e: {{cite web |url=http://www.accessmedicine.com/content.aspx?aID=6182422 |title=Archived copy |accessdate=2015-02-24 |deadurl=yes |archiveurl=https://web.archive.org/web/20130603013209/http://www.accessmedicine.com/content.aspx?aid=6182422 |archivedate=2013-06-03 |df= }}.</ref> This designation is due to the arrangement of the multiple cell types composing the respiratory epithelium. While all cells make contact with the [[basement membrane]] and are, therefore, a single layer of cells, the nuclei are not aligned in the same plane. Hence, it appears as though several layers of cells are present and the epithelium is called ''[[Epithelium#Pseudostratified|pseudostratified]]''.
The majority of cells composing the ciliated [[pseudostratified columnar epithelium]] are of three types: a) [[cilium|ciliated cells]], b) [[goblet cells]], and c) [[keratinocyte|basal cells]]. The ciliated cells are [[columnar epithelial cell]]s with specialized ciliary modifications. [[Goblet cells]], so named because they are shaped like a wine goblet, are [[columnar epithelial cell]]s that contain membrane-bound mucous granules and secrete [[mucus]], or epithelial lining fluid (ELF), the composition of which is tightly regulated; the mucus helps maintain epithelial moisture and traps particulate material and pathogens moving through the airway. and determines how well [[mucociliary clearance]] works.<ref>Stanke F The Contribution of the Airway Epithelial Cell to Host Defense. Mediators Inflamm. 2015;2015:463016. {{PMID|26185361}} [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4491388/ PMC 4491388]</ref><ref name=EPAassess2016>U.S. EPA. Integrated Science Assessment for Oxides of Nitrogen – Health Criteria (2016 Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-15/068, 2016. [https://www.federalregister.gov/articles/2016/01/28/2016-01548/integrated-science-assessment-for-oxides-of-nitrogen-health-criteria Federal Register Notice Jan 28, 2016] Free download available at [https://cfpub.epa.gov/ncea/isa/recordisplay.cfm?deid=310879 Report page at EPA website].</ref>
Other cells of the respiratory epithelium include [[brush cells]], which are columnar cells with microvilli that function as chemoreceptors, and small granule cells ([[Kulchitsky cells]]), which are neuroendocrine cells.<ref>{{Cite book|title=Histology: A Text and Atlas, with Correlated Cell and Molecular Biology, 7th Edition|last=|first=|publisher=|year=|isbn=|location=|pages=664}}</ref>
Certain parts of the [[respiratory tract]], such as the [[pharynx#Oropharynx|oropharynx]], are also subject to the abrasive swallowing of food. To prevent the destruction of the respiratory epithelium in these areas, it changes to [[stratified squamous epithelium]], which is better suited to the constant [[desquamation|sloughing]] and abrasion. The squamous layer of the oropharynx is continuous with the [[esophagus]].{{Citation needed|date=March 2010}}
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