Editing Lung (section)

=== Protection ===
The lungs possess several characteristics which protect against infection. The respiratory tract is lined by [[respiratory epithelium]] or respiratory mucosa, with hair-like projections called [[cilia]] that beat rhythmically and carry [[mucus]]. This [[mucociliary clearance]] is an important defence system against air-borne infection.<ref name=pmid26475269/> The dust particles and bacteria in the inhaled air are caught in the mucosal surface of the airways, and are moved up towards the pharynx by the rhythmic upward beating action of the cilia.<ref name=PAWLINA /><ref name=DAVIDSONS2014 />{{rp|661–730}} The lining of the lung also secretes [[immunoglobulin A]] which protects against respiratory infections;<ref name=DAVIDSONS2014 /> [[goblet cells]] secrete mucus<ref name=PAWLINA /> which also contains several antimicrobial compounds such as [[defensin]]s, [[antiprotease]]s, and [[antioxidant]]s.<ref name=DAVIDSONS2014 /> A rare type of specialised cell called a '''pulmonary ionocyte''' that is suggested may regulate mucus viscosity has been described.<ref>{{Cite journal |display-authors=1 | doi = 10.1038/s41586-018-0393-7 | pmid = 30069044 | pmc = 6295155 | title = A revised airway epithelial hierarchy includes CFTR-expressing ionocytes | journal = Nature | volume = 560 | issue = 7718 | pages = 319–324 | year = 2018 | last1 = Montoro | first1 = Daniel T | last2 = Haber | first2 = Adam L | last3 = Biton | first3 = Moshe | last4 = Vinarsky | first4 = Vladimir | last5 = Lin | first5 = Brian | last6 = Birket | first6 = Susan E | last7 = Yuan | first7 = Feng | last8 = Chen | first8 = Sijia | last9 = Leung | first9 = Hui Min | last10 = Villoria | first10 = Jorge | last11 = Rogel | first11 = Noga | last12 = Burgin | first12 = Grace | last13 = Tsankov | first13 = Alexander M | last14 = Waghray | first14 = Avinash | last15 = Slyper | first15 = Michal | last16 = Waldman | first16 = Julia | last17 = Nguyen | first17 = Lan | last18 = Dionne | first18 = Danielle | last19 = Rozenblatt-Rosen | first19 = Orit | last20 = Tata | first20 = Purushothama Rao | last21 = Mou | first21 = Hongmei | last22 = Shivaraju | first22 = Manjunatha | last23 = Bihler | first23 = Hermann | last24 = Mense | first24 = Martin | last25 = Tearney | first25 = Guillermo J | last26 = Rowe | first26 = Steven M | last27 = Engelhardt | first27 = John F | last28 = Regev | first28 = Aviv | last29 = Rajagopal | first29 = Jayaraj| bibcode = 2018Natur.560..319M }}</ref><ref>{{Cite journal |display-authors=1 | doi = 10.1038/s41586-018-0394-6 | pmid = 30069046 | pmc = 6108322 | title = A single-cell atlas of the airway epithelium reveals the CFTR-rich pulmonary ionocyte | journal = Nature | volume = 560|issue = 7718 | pages = 377–381 | year = 2018 | last1 = Plasschaert | first1 = LW | last2 = Zillionis | first2 = R | last3 = Choo-Wing | first3 = R | last4 = Savova | first4 = V | last5 = Knehr | first5 = J | last6 = Roma | first6 = G | last7 = Klein | first7 = AM | last8 = Jaffe | first8 = AB| bibcode = 2018Natur.560..377P }}</ref><ref name="CFN">{{cite web |title=CF Study Finds New Cells Called Ionocytes Carrying High levels of CFTR Gene |url=https://cysticfibrosisnewstoday.com/2018/08/03/cf-study-finds-new-cells-ionocytes-carrying-high-cftr-levels/ |website=Cystic Fibrosis News Today |date=3 August 2018}}</ref> In addition, the lining of the lung also contains [[macrophage]]s, immune cells which engulf and destroy debris and microbes that enter the lung in a process known as [[phagocytosis]]; and [[dendritic cell]]s which present antigens to activate components of the [[adaptive immune system]] such as [[T cell]]s and [[B cell]]s.<ref name=DAVIDSONS2014 />

The size of the respiratory tract and the flow of air also protect the lungs from larger particles. Smaller particles deposit in the [[human mouth|mouth]] and behind the mouth in the [[Pharynx#Oropharynx|oropharynx]], and larger particles are trapped in [[nasal hair]] after inhalation.<ref name=DAVIDSONS2014 />