Editing Trachea (section)

===Microanatomy===
The trachea is lined with a layer of [[pseudostratified ciliated columnar epithelium|interspersed layers of column-shaped cells with cilia]].<ref name="Furlow2018" /> The [[epithelium]] contains [[goblet cell]]s,  which are [[gland]]ular, column-shaped cells that produce [[mucins]], the main component of [[mucus]]. Mucus helps to moisten and protect the airways.<ref>{{cite book | vauthors = Mescher AL | chapter = Chapter 17. The Respiratory System | veditors = Mescher AL | title = Junqueira's Basic Histology: Text & Atlas | date = 28 August 2009 | publisher = McGraw Hill Professional | edition = 12th | url = http://www.accessmedicine.com/content.aspx?aID=6182422 |access-date=2015-02-24 |url-status=dead |archive-url=https://web.archive.org/web/20130603013209/http://www.accessmedicine.com/content.aspx?aid=6182422 |archive-date=3 June 2013 | isbn = 978-0-07-163020-7 }}</ref> Mucus lines the [[ciliated]] cells of the trachea to trap inhaled foreign particles that the cilia then waft upward toward the larynx and then the pharynx where it can be either swallowed into the [[stomach]] or expelled as [[phlegm]]. This self-clearing mechanism is termed [[mucociliary clearance]].<ref>{{cite journal | vauthors = Antunes MB, Cohen NA | title = Mucociliary clearance--a critical upper airway host defense mechanism and methods of assessment | journal = Current Opinion in Allergy and Clinical Immunology | volume = 7 | issue = 1 | pages = 5–10 | date = February 2007 | pmid = 17218804 | doi = 10.1097/aci.0b013e3280114eef | s2cid = 9551913 }}</ref> Directly beneath this mucus layer lies the submucosa layer which is composed primarily of fibrous connective tissue and connects the mucosa to the rings of hyaline cartilage beneath.<ref>Ayyalasomayajula, Venkat, and Bjørn Skallerud. “Microstructure and Mechanics of the Bovine Trachea: Layer Specific Investigations through SHG Imaging and Biaxial Testing.” Journal of the Mechanical Behavior of Biomedical Materials, vol. 134, 1 Oct. 2022, p. 5, https://doi.org/10.1016/j.jmbbm.2022.105371.</ref>

The trachea is surrounded by 16 to 20 rings of hyaline cartilage; these 'rings' are incomplete and C-shaped.<ref name=GA2016 /> Two or more of the cartilages often unite, partially or completely, and they are sometimes bifurcated at their extremities. The rings are generally highly elastic but they may [[calcification|calcify]] with [[ageing|age]].
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File:Gray964.png|Cross-section
File:2308 The Trachea-b.jpg|Cross-section of the trachea, with pseudostratified ciliated columnar epithelium and goblet cells labelled
File:Cartilage01.JPG|Magnified cross-section of the cartilage of the trachea 
</gallery>