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class="vector-toc-list"> <li id="toc-Upper_respiratory_tract" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Upper_respiratory_tract"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1</span> <span>Upper respiratory tract</span> </div> </a> <ul id="toc-Upper_respiratory_tract-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Lower_respiratory_tract" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Lower_respiratory_tract"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.2</span> <span>Lower respiratory tract</span> </div> </a> <ul id="toc-Lower_respiratory_tract-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Microanatomy" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Microanatomy"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.3</span> <span>Microanatomy</span> </div> </a> <ul id="toc-Microanatomy-sublist" 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class="vector-toc-link" href="#Defences_against_infection"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2</span> <span>Defences against infection</span> </div> </a> <ul id="toc-Defences_against_infection-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Clinical_significance" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Clinical_significance"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Clinical significance</span> </div> </a> <button aria-controls="toc-Clinical_significance-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Clinical significance subsection</span> </button> <ul id="toc-Clinical_significance-sublist" class="vector-toc-list"> <li id="toc-Infection" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Infection"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>Infection</span> </div> </a> <ul id="toc-Infection-sublist" class="vector-toc-list"> <li id="toc-Upper_respiratory_infection" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Upper_respiratory_infection"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1.1</span> <span>Upper respiratory infection</span> </div> </a> <ul id="toc-Upper_respiratory_infection-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Lower_respiratory_tract_infections" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Lower_respiratory_tract_infections"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1.2</span> <span>Lower respiratory tract infections</span> </div> </a> <ul id="toc-Lower_respiratory_tract_infections-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Cancer" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Cancer"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>Cancer</span> </div> </a> <ul id="toc-Cancer-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-COPD" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#COPD"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>COPD</span> </div> </a> <ul id="toc-COPD-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Asthma" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Asthma"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.4</span> <span>Asthma</span> </div> </a> <ul id="toc-Asthma-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Mouth_breathing" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Mouth_breathing"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.5</span> <span>Mouth breathing</span> </div> </a> <ul id="toc-Mouth_breathing-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" 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class="firstHeading mw-first-heading"><span class="mw-page-title-main">Respiratory tract</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. 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href="https://az.wikipedia.org/wiki/T%C9%99n%C9%99ff%C3%BCs_aparat%C4%B1" title="Tənəffüs aparatı – Azerbaijani" lang="az" hreflang="az" data-title="Tənəffüs aparatı" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/D%C3%BDchac%C3%AD_cesty" title="Dýchací cesty – Czech" lang="cs" hreflang="cs" data-title="Dýchací cesty" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-se mw-list-item"><a href="https://se.wikipedia.org/wiki/Vuoi%C5%8B%C5%8Bahat" title="Vuoiŋŋahat – Northern Sami" lang="se" hreflang="se" data-title="Vuoiŋŋahat" data-language-autonym="Davvisámegiella" data-language-local-name="Northern Sami" class="interlanguage-link-target"><span>Davvisámegiella</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Hingamisteed" title="Hingamisteed – Estonian" lang="et" hreflang="et" data-title="Hingamisteed" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/V%C3%ADa_a%C3%A9rea_(anatom%C3%ADa)" title="Vía aérea (anatomía) – Spanish" lang="es" hreflang="es" data-title="Vía aérea (anatomía)" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Arnasbide" title="Arnasbide – Basque" lang="eu" hreflang="eu" data-title="Arnasbide" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%B1%D8%A7%D9%87_%D9%87%D9%88%D8%A7%DB%8C%DB%8C" title="راه هوایی – Persian" lang="fa" hreflang="fa" data-title="راه هوایی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Voies_respiratoires" title="Voies respiratoires – French" lang="fr" hreflang="fr" data-title="Voies respiratoires" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EA%B8%B0%EB%8F%84_(%EC%9D%98%ED%95%99)" title="기도 (의학) – Korean" lang="ko" hreflang="ko" data-title="기도 (의학)" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%B6%E0%A5%8D%E0%A4%B5%E0%A4%B8%E0%A4%A8_%E0%A4%AA%E0%A4%A5" title="श्वसन पथ – Hindi" lang="hi" hreflang="hi" data-title="श्वसन पथ" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Saluran_napas" title="Saluran napas – Indonesian" lang="id" hreflang="id" data-title="Saluran napas" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-kn mw-list-item"><a href="https://kn.wikipedia.org/wiki/%E0%B2%89%E0%B2%B8%E0%B2%BF%E0%B2%B0%E0%B2%BE%E0%B2%9F%E0%B2%A6_%E0%B2%AE%E0%B2%82%E0%B2%A1%E0%B2%B2%E0%B2%A6_%E0%B2%85%E0%B2%82%E0%B2%97%E0%B2%B0%E0%B2%9A%E0%B2%A8%E0%B3%86" title="ಉಸಿರಾಟದ ಮಂಡಲದ ಅಂಗರಚನೆ – Kannada" lang="kn" hreflang="kn" data-title="ಉಸಿರಾಟದ ಮಂಡಲದ ಅಂಗರಚನೆ" data-language-autonym="ಕನ್ನಡ" data-language-local-name="Kannada" class="interlanguage-link-target"><span>ಕನ್ನಡ</span></a></li><li class="interlanguage-link interwiki-ku mw-list-item"><a href="https://ku.wikipedia.org/wiki/Coga_henasey%C3%AA" title="Coga henaseyê – Kurdish" lang="ku" hreflang="ku" data-title="Coga henaseyê" data-language-autonym="Kurdî" data-language-local-name="Kurdish" class="interlanguage-link-target"><span>Kurdî</span></a></li><li class="interlanguage-link interwiki-la mw-list-item"><a href="https://la.wikipedia.org/wiki/Apparatus_respiratorius" title="Apparatus respiratorius – Latin" lang="la" hreflang="la" data-title="Apparatus respiratorius" data-language-autonym="Latina" data-language-local-name="Latin" class="interlanguage-link-target"><span>Latina</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Kv%C4%97pavimo_takai" title="Kvėpavimo takai – Lithuanian" lang="lt" hreflang="lt" data-title="Kvėpavimo takai" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Luchtwegen" title="Luchtwegen – Dutch" lang="nl" hreflang="nl" data-title="Luchtwegen" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E6%B0%97%E9%81%93" title="気道 – Japanese" lang="ja" hreflang="ja" data-title="気道" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Drogi_oddechowe" title="Drogi oddechowe – Polish" lang="pl" hreflang="pl" data-title="Drogi oddechowe" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Via_respirat%C3%B3ria" title="Via respiratória – Portuguese" lang="pt" hreflang="pt" data-title="Via respiratória" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Respiratory_tract" title="Respiratory tract – Simple English" lang="en-simple" hreflang="en-simple" data-title="Respiratory tract" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Dihalna_pot" title="Dihalna pot – Slovenian" lang="sl" hreflang="sl" data-title="Dihalna pot" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Hengitystiet" title="Hengitystiet – Finnish" lang="fi" hreflang="fi" data-title="Hengitystiet" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Luftv%C3%A4g" title="Luftväg – Swedish" lang="sv" hreflang="sv" data-title="Luftväg" 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class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/%C4%90%C6%B0%E1%BB%9Dng_h%C3%B4_h%E1%BA%A5p" title="Đường hô hấp – Vietnamese" lang="vi" hreflang="vi" data-title="Đường hô hấp" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E5%91%BC%E5%90%B8%E9%81%93" title="呼吸道 – Chinese" lang="zh" hreflang="zh" data-title="呼吸道" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q13400765#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div 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For an aerial route taken by airplanes, see <a href="/wiki/Airway_(aviation)" title="Airway (aviation)">Airway (aviation)</a>. For other uses, see <a href="/wiki/Airway_(disambiguation)" class="mw-disambig" title="Airway (disambiguation)">Airway (disambiguation)</a>.</div> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox"><tbody><tr><th colspan="2" class="infobox-above" style="background-color:dimgray; color: white">Respiratory tract</th></tr><tr><td colspan="2" class="infobox-image"><span class="mw-default-size" typeof="mw:File/Frameless"><a href="/wiki/File:Illu_conducting_passages.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/9f/Illu_conducting_passages.svg/250px-Illu_conducting_passages.svg.png" decoding="async" width="250" height="322" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/9f/Illu_conducting_passages.svg/375px-Illu_conducting_passages.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/9f/Illu_conducting_passages.svg/500px-Illu_conducting_passages.svg.png 2x" data-file-width="255" data-file-height="328" /></a></span><div class="infobox-caption">Conducting passages</div></td></tr><tr><th colspan="2" class="infobox-header" style="background-color: #efefef">Details</th></tr><tr><th scope="row" class="infobox-label" style="padding-right:0.25em"><a href="/wiki/Organ_system" title="Organ system">System</a></th><td class="infobox-data"><a href="/wiki/Respiratory_system" title="Respiratory system">Respiratory system</a></td></tr><tr><th colspan="2" class="infobox-header" style="background-color: #efefef">Identifiers</th></tr><tr><th scope="row" class="infobox-label" style="padding-right:0.25em"><a href="/wiki/Foundational_Model_of_Anatomy" title="Foundational Model of Anatomy">FMA</a></th><td class="infobox-data"><a rel="nofollow" class="external text" href="https://bioportal.bioontology.org/ontologies/FMA/?p=classes&conceptid=http%3A%2F%2Fpurl.org%2Fsig%2Font%2Ffma%2Ffma265130">265130</a></td></tr><tr><td colspan="2" class="infobox-below"><a href="/wiki/Anatomical_terminology" title="Anatomical terminology">Anatomical terminology</a><div style="text-align: right;"><small class="noprint">[<a href="https://www.wikidata.org/wiki/Q13400765" class="extiw" title="d:Q13400765">edit on Wikidata</a>]</small></div></td></tr></tbody></table> <p>The <b>respiratory tract</b> is the subdivision of the <a href="/wiki/Respiratory_system" title="Respiratory system">respiratory system</a> involved with the process of conducting air to the <a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">alveoli</a> for the purposes of <a href="/wiki/Gas_exchange" title="Gas exchange">gas exchange</a> in <a href="/wiki/Mammal" title="Mammal">mammals</a>.<sup id="cite_ref-Patwa_1-0" class="reference"><a href="#cite_note-Patwa-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> The respiratory tract is lined with <a href="/wiki/Respiratory_epithelium" title="Respiratory epithelium">respiratory epithelium</a> as respiratory mucosa.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p><p>Air is breathed in through the <a href="/wiki/Nose" title="Nose">nose</a> to the <a href="/wiki/Nasal_cavity" title="Nasal cavity">nasal cavity</a>, where a layer of <a href="/wiki/Nasal_mucosa" title="Nasal mucosa">nasal mucosa</a> acts as a filter and traps pollutants and other harmful substances found in the air. Next, air moves into the <a href="/wiki/Pharynx" title="Pharynx">pharynx</a>, a passage that contains the intersection between the <a href="/wiki/Esophagus" title="Esophagus">oesophagus</a> and the <a href="/wiki/Larynx" title="Larynx">larynx</a>. The opening of the larynx has a special flap of cartilage, the <a href="/wiki/Epiglottis" title="Epiglottis">epiglottis</a>, that opens to allow air to pass through but closes to prevent food from moving into the airway. </p><p>From the <a href="/wiki/Larynx" title="Larynx">larynx</a>, air moves into the <a href="/wiki/Trachea" title="Trachea">trachea</a> and down to the intersection known as the <a href="/wiki/Carina_of_trachea" title="Carina of trachea">carina</a> that branches to form the right and left primary (main) <a href="/wiki/Bronchus" title="Bronchus">bronchi</a>. Each of these bronchi branches into a <a href="/wiki/Bronchus" title="Bronchus">secondary (lobar) bronchus</a> that branches into <a href="/wiki/Bronchus" title="Bronchus">tertiary (segmental) bronchi</a>, that branch into smaller airways called <a href="/wiki/Bronchiole" title="Bronchiole">bronchioles</a> that eventually connect with tiny specialized structures called <a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">alveoli</a> that function in <a href="/wiki/Gas_exchange" title="Gas exchange">gas exchange</a>. </p><p>The <a href="/wiki/Lung" title="Lung">lungs</a> which are located in the <a href="/wiki/Thoracic_cavity" title="Thoracic cavity">thoracic cavity</a>, are protected from physical damage by the <a href="/wiki/Rib_cage" title="Rib cage">rib cage</a>. At the base of the lungs is a sheet of skeletal muscle called the <a href="/wiki/Thoracic_diaphragm" title="Thoracic diaphragm">diaphragm</a>. The diaphragm separates the lungs from the <a href="/wiki/Stomach" title="Stomach">stomach</a> and <a href="/wiki/Gastrointestinal_tract" title="Gastrointestinal tract">intestines</a>. The diaphragm is also the main <a href="/wiki/Muscles_of_respiration" title="Muscles of respiration">muscle of respiration</a> involved in <a href="/wiki/Breathing" title="Breathing">breathing</a>, and is controlled by the <a href="/wiki/Sympathetic_nervous_system" title="Sympathetic nervous system">sympathetic nervous system</a>. </p><p>The lungs are encased in a <a href="/wiki/Serous_membrane" title="Serous membrane">serous membrane</a> that folds in on itself to form the <a href="/wiki/Pulmonary_pleurae" class="mw-redirect" title="Pulmonary pleurae">pleurae</a> – a two-layered protective barrier. The inner <a href="/wiki/Pulmonary_pleurae" class="mw-redirect" title="Pulmonary pleurae">visceral pleura</a> covers the surface of the lungs, and the outer <a href="/wiki/Pulmonary_pleurae" class="mw-redirect" title="Pulmonary pleurae">parietal pleura</a> is attached to the inner surface of the thoracic cavity. The pleurae enclose a cavity called the <a href="/wiki/Pleural_cavity" title="Pleural cavity">pleural cavity</a> that contains <a href="/wiki/Pleural_cavity#Pleural_fluid" title="Pleural cavity">pleural fluid</a>. This fluid is used to decrease the amount of friction that lungs experience during breathing. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Structure">Structure</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=1" title="Edit section: Structure"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Respiratory_system_complete_en.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5e/Respiratory_system_complete_en.svg/260px-Respiratory_system_complete_en.svg.png" decoding="async" width="260" height="277" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5e/Respiratory_system_complete_en.svg/390px-Respiratory_system_complete_en.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5e/Respiratory_system_complete_en.svg/520px-Respiratory_system_complete_en.svg.png 2x" data-file-width="512" data-file-height="545" /></a><figcaption>Complete respiratory system</figcaption></figure> <p>The respiratory tract is divided into the <b>upper airways</b> and <b>lower airways</b>. The upper airways or upper respiratory tract includes the <a href="/wiki/Human_nose" title="Human nose">nose</a> and nasal passages, <a href="/wiki/Paranasal_sinus" class="mw-redirect" title="Paranasal sinus">paranasal sinuses</a>, the <a href="/wiki/Pharynx" title="Pharynx">pharynx</a>, and the portion of the <a href="/wiki/Larynx" title="Larynx">larynx</a> above the <a href="/wiki/Vocal_folds" class="mw-redirect" title="Vocal folds">vocal folds</a> (cords). The lower airways or lower respiratory tract includes the portion of the larynx below the vocal folds, <a href="/wiki/Trachea" title="Trachea">trachea</a>, <a href="/wiki/Bronchus" title="Bronchus">bronchi</a> and <a href="/wiki/Bronchiole" title="Bronchiole">bronchioles</a>. The lungs can be included in the lower respiratory tract or as separate entity and include the respiratory bronchioles, <a href="/wiki/Alveolar_duct" class="mw-redirect" title="Alveolar duct">alveolar ducts</a>, <a href="/wiki/Alveolar_sac" class="mw-redirect" title="Alveolar sac">alveolar sacs</a>, and <a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">alveoli</a>.<sup id="cite_ref-Def_3-0" class="reference"><a href="#cite_note-Def-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Adult_and_pediatric_airway_anatomy.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/51/Adult_and_pediatric_airway_anatomy.png/220px-Adult_and_pediatric_airway_anatomy.png" decoding="async" width="220" height="255" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/51/Adult_and_pediatric_airway_anatomy.png/330px-Adult_and_pediatric_airway_anatomy.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/51/Adult_and_pediatric_airway_anatomy.png/440px-Adult_and_pediatric_airway_anatomy.png 2x" data-file-width="3281" data-file-height="3809" /></a><figcaption>Adult and pediatric airway anatomy</figcaption></figure> <p>The respiratory tract can also be divided into a <b>conducting zone</b> and a <b>respiratory zone</b>, based on the distinction of transporting gases or <a href="/wiki/Gas_exchange" title="Gas exchange">exchanging</a> them. </p><p>The conducting zone includes structures outside of the lungs – the <a href="/wiki/Nose" title="Nose">nose</a>, <a href="/wiki/Pharynx" title="Pharynx">pharynx</a>, <a href="/wiki/Larynx" title="Larynx">larynx</a>, and <a href="/wiki/Trachea" title="Trachea">trachea</a>, and structures inside the lungs – the bronchi, bronchioles, and terminal bronchioles. The conduction zone conducts air breathed in that is filtered, warmed, and moistened, into the lungs. It represents the 1st through the 16th division of the respiratory tract. The conducting zone is most of the respiratory tract that conducts gases into and out of the lungs but excludes the respiratory zone that exchanges gases. The conducting zone also functions to offer a low resistance pathway for airflow. It provides a major <a href="/wiki/Immune_system" title="Immune system">defense role</a> in its filtering abilities. </p><p>The respiratory zone includes the respiratory bronchioles, alveolar ducts, and alveoli, and is the site of oxygen and carbon dioxide <a href="/wiki/Gas_exchange" title="Gas exchange">exchange</a> with the blood. The respiratory bronchioles and the alveolar ducts are responsible for 10% of the gas exchange. The alveoli are responsible for the other 90%. The respiratory zone represents the 16th through the 23rd division of the respiratory tract. </p><p>From the bronchi, the dividing tubes become progressively smaller with an estimated 20 to 23 divisions before ending at an alveolus.<sup id="cite_ref-Patwa_1-1" class="reference"><a href="#cite_note-Patwa-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Upper_respiratory_tract">Upper respiratory tract</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=2" title="Edit section: Upper respiratory tract"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Blausen_0872_UpperRespiratorySystem.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Blausen_0872_UpperRespiratorySystem.png/170px-Blausen_0872_UpperRespiratorySystem.png" decoding="async" width="170" height="150" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Blausen_0872_UpperRespiratorySystem.png/255px-Blausen_0872_UpperRespiratorySystem.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Blausen_0872_UpperRespiratorySystem.png/340px-Blausen_0872_UpperRespiratorySystem.png 2x" data-file-width="2500" data-file-height="2200" /></a><figcaption>Details of upper respiratory tract</figcaption></figure> <p>The <b>upper respiratory tract</b> can refer to the parts of the <a href="/wiki/Respiratory_system" title="Respiratory system">respiratory system</a> lying above the <a href="/wiki/Vocal_folds" class="mw-redirect" title="Vocal folds">vocal folds</a>, or above the <a href="/wiki/Cricoid_cartilage" title="Cricoid cartilage">cricoid cartilage</a>.<sup id="cite_ref-PerkinSwift2007_4-0" class="reference"><a href="#cite_note-PerkinSwift2007-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-WardWard2006_5-0" class="reference"><a href="#cite_note-WardWard2006-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/Larynx" title="Larynx">larynx</a> is sometimes included in both the upper and lower airways.<sup id="cite_ref-Sircar2008_6-0" class="reference"><a href="#cite_note-Sircar2008-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> The larynx is also called the voice box and has the associated cartilage that produces sound. The tract consists of the <a href="/wiki/Nasal_cavity" title="Nasal cavity">nasal cavity</a> and <a href="/wiki/Paranasal_sinus" class="mw-redirect" title="Paranasal sinus">paranasal sinuses</a>, the <a href="/wiki/Pharynx" title="Pharynx">pharynx</a> (<a href="/wiki/Nasopharynx" class="mw-redirect" title="Nasopharynx">nasopharynx</a>, <a href="/wiki/Oropharynx" class="mw-redirect" title="Oropharynx">oropharynx</a> and <a href="/wiki/Laryngopharynx" class="mw-redirect" title="Laryngopharynx">laryngopharynx</a>) and sometimes includes the larynx. </p> <div class="mw-heading mw-heading3"><h3 id="Lower_respiratory_tract">Lower respiratory tract</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=3" title="Edit section: Lower respiratory tract"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Diagram_showing_the_parts_of_the_respiratory_system_CRUK_335.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/21/Diagram_showing_the_parts_of_the_respiratory_system_CRUK_335.svg/220px-Diagram_showing_the_parts_of_the_respiratory_system_CRUK_335.svg.png" decoding="async" width="220" height="168" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/21/Diagram_showing_the_parts_of_the_respiratory_system_CRUK_335.svg/330px-Diagram_showing_the_parts_of_the_respiratory_system_CRUK_335.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/21/Diagram_showing_the_parts_of_the_respiratory_system_CRUK_335.svg/440px-Diagram_showing_the_parts_of_the_respiratory_system_CRUK_335.svg.png 2x" data-file-width="375" data-file-height="286" /></a><figcaption>Parts of the lower respiratory tract</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Illu_quiz_lung05.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/df/Illu_quiz_lung05.jpg/180px-Illu_quiz_lung05.jpg" decoding="async" width="180" height="233" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/d/df/Illu_quiz_lung05.jpg 1.5x" data-file-width="270" data-file-height="350" /></a><figcaption><div><ol><li><a href="/wiki/Vertebrate_trachea" class="mw-redirect" title="Vertebrate trachea">Trachea</a></li><li><a href="/wiki/Main_bronchus" class="mw-redirect" title="Main bronchus">Mainstem bronchus</a></li><li><a href="/wiki/Secondary_bronchus" class="mw-redirect" title="Secondary bronchus">Lobar bronchus</a></li><li><a href="/wiki/Tertiary_bronchus" class="mw-redirect" title="Tertiary bronchus">Segmental bronchus</a></li><li><a href="/wiki/Bronchiole" title="Bronchiole">Bronchiole</a></li><li><a href="/wiki/Alveolar_duct" class="mw-redirect" title="Alveolar duct">Alveolar duct</a></li><li><a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">Alveolus</a></li></ol></div></figcaption></figure><p>The <b>lower respiratory tract</b> or <b>lower airway</b> is derived from the developing <a href="/wiki/Foregut" title="Foregut">foregut</a> and consists of the <a href="/wiki/Trachea" title="Trachea">trachea</a>, <a href="/wiki/Bronchus" title="Bronchus">bronchi</a> (primary, secondary and tertiary), <a href="/wiki/Bronchioles" class="mw-redirect" title="Bronchioles">bronchioles</a> (including terminal and respiratory), and <a href="/wiki/Human_lung" class="mw-redirect" title="Human lung">lungs</a> (including <a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">alveoli</a>).<sup id="cite_ref-medscape_7-0" class="reference"><a href="#cite_note-medscape-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> It also sometimes includes the larynx. </p><p>The lower respiratory tract is also called the <b>respiratory tree</b> or <b>tracheobronchial tree</b>, to describe the branching structure of airways supplying air to the lungs, and includes the trachea, bronchi and bronchioles.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p> <ul><li><a href="/wiki/Trachea" title="Trachea">trachea</a> <ul><li>main <a href="/wiki/Bronchus" title="Bronchus">bronchus</a> (diameter approximately 1 – 1.4 cm in adults)<sup id="cite_ref-kacmarek_9-0" class="reference"><a href="#cite_note-kacmarek-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> <ul><li><a href="/wiki/Lobar_bronchus" class="mw-redirect" title="Lobar bronchus">lobar bronchus</a> (diameter approximately 1 cm) <ul><li><a href="/wiki/Segmental_bronchus" class="mw-redirect" title="Segmental bronchus">segmental bronchus</a> (diameter 4.5 to 13 mm)<sup id="cite_ref-kacmarek_9-1" class="reference"><a href="#cite_note-kacmarek-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> <ul><li>subsegmental bronchus (diameter 1 to 6 mm)<sup id="cite_ref-kacmarek_9-2" class="reference"><a href="#cite_note-kacmarek-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> <ul><li>conducting <a href="/wiki/Bronchiole" title="Bronchiole">bronchiole</a> <ul><li><a href="/wiki/Terminal_bronchiole" class="mw-redirect" title="Terminal bronchiole">terminal bronchiole</a> <ul><li><a href="/wiki/Respiratory_bronchiole" class="mw-redirect" title="Respiratory bronchiole">respiratory bronchiole</a> <ul><li><a href="/wiki/Alveolar_duct" class="mw-redirect" title="Alveolar duct">alveolar duct</a> <ul><li><a href="/wiki/Alveolar_sac" class="mw-redirect" title="Alveolar sac">alveolar sac</a> <ul><li><a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">alveolus</a></li></ul></li></ul></li></ul></li></ul></li></ul></li></ul></li></ul></li></ul></li></ul></li></ul></li></ul> <p>At each division point or <b>generation</b>, one airway branches into two smaller airways. The human respiratory tree may consist on average of 23 generations, while the respiratory tree of the <a href="/wiki/Mouse" title="Mouse">mouse</a> has up to 13 generations. Proximal divisions (those closest to the top of the tree, such as the bronchi) mainly function to transmit air to the lower airways. Later divisions including the respiratory bronchiole, alveolar ducts, and alveoli, are specialized for <a href="/wiki/Gas_exchange" title="Gas exchange">gas exchange</a>. </p><p>The <b>trachea</b> is the largest tube in the respiratory tract and consists of <a href="/wiki/Tracheal_ring" class="mw-redirect" title="Tracheal ring">tracheal rings</a> of <a href="/wiki/Hyaline_cartilage" title="Hyaline cartilage">hyaline cartilage</a>. It branches off into two bronchial tubes, a left and a right main <a href="/wiki/Bronchus" title="Bronchus">bronchus</a>. The bronchi branch off into smaller sections inside the lungs, called <a href="/wiki/Bronchioles" class="mw-redirect" title="Bronchioles">bronchioles</a>. These bronchioles give rise to the air sacs in the lungs called the <a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">alveoli</a>.<sup id="cite_ref-lungusa_10-0" class="reference"><a href="#cite_note-lungusa-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p><p>The <b>lungs</b> are the largest organs in the lower respiratory tract. The lungs are suspended within the <a href="/wiki/Pleural_cavity" title="Pleural cavity">pleural cavity</a> of the thorax. The <a href="/wiki/Pleurae" class="mw-redirect" title="Pleurae">pleurae</a> are two thin membranes, one cell layer thick, which surround the lungs. The inner (<a href="/wiki/Visceral_pleura" class="mw-redirect" title="Visceral pleura">visceral pleura</a>) covers the lungs and the outer (<a href="/wiki/Parietal_pleura" class="mw-redirect" title="Parietal pleura">parietal pleura</a>) lines the inner surface of the chest wall. This membrane secretes a small amount of fluid, allowing the lungs to move freely within the pleural cavity while expanding and contracting during breathing. The lungs are divided into different lobes. The right lung is larger in size than the left, because of the heart's being situated to the left of the midline. The right lung has three lobes – upper, middle, and lower (or superior, middle, and inferior), and the left lung has two – upper and lower (or superior and inferior), plus a small tongue-shaped portion of the upper lobe known as the lingula. Each lobe is further divided up into segments called <a href="/wiki/Bronchopulmonary_segment" title="Bronchopulmonary segment">bronchopulmonary segments</a>. Each lung has a costal surface, which is adjacent to the ribcage; a diaphragmatic surface, which faces downward toward the diaphragm; and a mediastinal surface, which faces toward the center of the chest, and lies against the heart, great vessels, and the carina where the two mainstem bronchi branch off from the base of the trachea. </p><p>The <b>alveoli</b> are tiny air sacs in the lungs where gas exchange takes place. The mean number of alveoli in a human lung is 480 million.<sup id="cite_ref-Ochs_11-0" class="reference"><a href="#cite_note-Ochs-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> When the diaphragm contracts, a negative pressure is generated in the thorax and air rushes in to fill the cavity. When that happens, these sacs fill with air, making the lung expand. The alveoli are rich with capillaries, called alveolar capillaries. Here the red blood cells absorb oxygen from the air and then carry it back in the form of oxyhaemaglobin, to nourish the cells. The red blood cells also carry carbon dioxide (CO<sub style="font-size: 80%;vertical-align: -0.35em">2</sub>) away from the cells in the form of <a href="/wiki/Carbaminohemoglobin" title="Carbaminohemoglobin">carbaminohemoglobin</a> and release it into the alveoli through the alveolar capillaries. When the diaphragm relaxes, a positive pressure is generated in the thorax and air rushes out of the alveoli expelling the carbon dioxide. </p> <div class="mw-heading mw-heading3"><h3 id="Microanatomy">Microanatomy</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=4" title="Edit section: Microanatomy"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Respiratory_epithelium" title="Respiratory epithelium">Respiratory epithelium</a></div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Blausen_0750_PseudostratifiedCiliatedColumnar.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/33/Blausen_0750_PseudostratifiedCiliatedColumnar.png/240px-Blausen_0750_PseudostratifiedCiliatedColumnar.png" decoding="async" width="240" height="250" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/33/Blausen_0750_PseudostratifiedCiliatedColumnar.png/360px-Blausen_0750_PseudostratifiedCiliatedColumnar.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/33/Blausen_0750_PseudostratifiedCiliatedColumnar.png/480px-Blausen_0750_PseudostratifiedCiliatedColumnar.png 2x" data-file-width="2400" data-file-height="2500" /></a><figcaption>Respiratory epithelium</figcaption></figure> <p>The respiratory tract is covered in <a href="/wiki/Epithelium" title="Epithelium">epithelium</a>, which varies down the tract. There are <a href="/wiki/Gland" title="Gland">glands</a> and <a href="/wiki/Mucus" title="Mucus">mucus</a> produced by <a href="/wiki/Goblet_cell" title="Goblet cell">goblet cells</a> in parts, as well as <a href="/wiki/Smooth_muscle" title="Smooth muscle">smooth muscle</a>, <a href="/wiki/Elastin" title="Elastin">elastin</a> or <a href="/wiki/Cartilage" title="Cartilage">cartilage</a>. The epithelium from the nose to the bronchioles is covered in ciliated <a href="/wiki/Pseudostratified_columnar_epithelium" title="Pseudostratified columnar epithelium">pseudostratified columnar epithelium</a>, commonly called <a href="/wiki/Respiratory_epithelium" title="Respiratory epithelium">respiratory epithelium</a>.<sup id="cite_ref-Moore04_12-0" class="reference"><a href="#cite_note-Moore04-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> The cilia beat in one direction, moving mucus towards the throat where it is swallowed. Moving down the bronchioles, the cells get more cuboidal in shape but are still ciliated. </p><p>Glands are abundant in the upper respiratory tract, but there are fewer lower down and they are absent starting at the bronchioles. The same goes for goblet cells, although there are scattered ones in the first bronchioles. </p><p>Cartilage is present until the bronchioles. In the trachea, they are C-shaped rings of <a href="/wiki/Hyaline_cartilage" title="Hyaline cartilage">hyaline cartilage</a>, whereas in the bronchi the cartilage takes the form of interspersed plates. Smooth muscle starts in the trachea, where it joins the C-shaped rings of cartilage. It continues down the <a href="/wiki/Bronchi" class="mw-redirect" title="Bronchi">bronchi</a> and <a href="/wiki/Bronchiole" title="Bronchiole">bronchioles</a>, which it completely encircles. Instead of hard cartilage, the bronchi and bronchioles are composed of elastic tissue. </p><p>The lungs are made up of thirteen different kinds of cells, eleven types of <a href="/wiki/Epithelium" title="Epithelium">epithelial</a> cell and two types of <a href="/wiki/Mesenchymal" class="mw-redirect" title="Mesenchymal">mesenchymal</a> cell.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> The epithelial cells form the lining of the tracheal, and bronchial tubes, while the mesenchymal cells line the lungs. </p> <ul class="gallery mw-gallery-traditional"> <li class="gallerybox" style="width: 155px"> <div class="thumb" style="width: 150px; height: 150px;"><span typeof="mw:File"><a href="/wiki/File:Respiratory_Tract_Histological_Differences.png" class="mw-file-description" title="Differences in cells along the respiratory tract"><img alt="Differences in cells along the respiratory tract" src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c8/Respiratory_Tract_Histological_Differences.png/120px-Respiratory_Tract_Histological_Differences.png" decoding="async" width="120" height="77" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c8/Respiratory_Tract_Histological_Differences.png/180px-Respiratory_Tract_Histological_Differences.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c8/Respiratory_Tract_Histological_Differences.png/240px-Respiratory_Tract_Histological_Differences.png 2x" data-file-width="1500" data-file-height="964" /></a></span></div> <div class="gallerytext">Differences in cells along the respiratory tract</div> </li> <li class="gallerybox" style="width: 155px"> <div class="thumb" style="width: 150px; height: 150px;"><span typeof="mw:File"><a href="/wiki/File:Gray964.png" class="mw-file-description" title="Transverse section of tracheal tissue. Note that image is incorrectly labeled "ciliated stratified epithelium" at upper right."><img alt="Transverse section of tracheal tissue. Note that image is incorrectly labeled "ciliated stratified epithelium" at upper right." src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Gray964.png/80px-Gray964.png" decoding="async" width="80" height="120" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Gray964.png/120px-Gray964.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Gray964.png/161px-Gray964.png 2x" data-file-width="402" data-file-height="600" /></a></span></div> <div class="gallerytext"> Transverse section of <a href="/wiki/Vertebrate_trachea" class="mw-redirect" title="Vertebrate trachea">tracheal</a> tissue. Note that image is incorrectly labeled "ciliated stratified epithelium" at upper right. </div> </li> </ul> <div class="mw-heading mw-heading2"><h2 id="Function">Function</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=5" title="Edit section: Function"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Most of the respiratory tract exists merely as a piping system for air to travel in the lungs, and <a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">alveoli</a> are the only part of the lung that <a href="/wiki/Gas_exchange" title="Gas exchange">exchanges</a> <a href="/wiki/Oxygen" title="Oxygen">oxygen</a> and <a href="/wiki/Carbon_dioxide" title="Carbon dioxide">carbon dioxide</a> with the <a href="/wiki/Blood" title="Blood">blood</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Respiration">Respiration</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=6" title="Edit section: Respiration"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Breathing" title="Breathing">Breathing</a></div> <p>Respiration is the <a href="/wiki/Neuroscience_of_rhythm" title="Neuroscience of rhythm">rhythmical process</a> of <a href="/wiki/Breathing" title="Breathing">breathing</a>, in which air is drawn into the alveoli of the lungs via <a href="/wiki/Inhalation" title="Inhalation">inhalation</a> and subsequently expelled via <a href="/wiki/Exhalation" title="Exhalation">exhalation</a>. When a human being inhales, air travels down the trachea, through the bronchial tubes, and into the lungs. The entire tract is protected by the rib cage, <a href="/wiki/Vertebral_column" class="mw-redirect" title="Vertebral column">spine</a>, and <a href="/wiki/Sternum" title="Sternum">sternum</a>. In the lungs, oxygen from the inhaled air is transferred into the blood and circulated throughout the body. Carbon dioxide (CO<sub>2</sub>) is transferred from returning blood back into gaseous form in the lungs and exhaled through the lower respiratory tract and then the upper, to complete the process of <a href="/wiki/Breathing" title="Breathing">breathing</a>. </p><p>Unlike the <a href="/wiki/Vertebrate_trachea" class="mw-redirect" title="Vertebrate trachea">trachea</a> and <a href="/wiki/Bronchus" title="Bronchus">bronchi</a>, the upper airway is a collapsible, compliant tube. As such, it has to be able to withstand suction pressures generated by the rhythmic expansion of the <a href="/wiki/Thoracic_cavity" title="Thoracic cavity">thoracic cavity</a> that sucks air into the lungs. This is accomplished by the contraction of upper airway muscles during inhalation, such as the <a href="/wiki/Genioglossus" title="Genioglossus">genioglossus</a> (tongue) and the <a href="/wiki/Hyoid" class="mw-redirect" title="Hyoid">hyoid</a> muscles. In addition to rhythmic innervation from the <a href="/wiki/Respiratory_center" title="Respiratory center">respiratory center</a> in the <a href="/wiki/Medulla_oblongata" title="Medulla oblongata">medulla oblongata</a>, the <a href="/wiki/Motor_neuron" title="Motor neuron">motor neurons</a> controlling the muscles also receive tonic innervation that sets a baseline level of stiffness and size. </p><p>The <a href="/wiki/Thoracic_diaphragm" title="Thoracic diaphragm">diaphragm</a> is the primary muscle that allows for lung expansion and contraction. Smaller muscles between the ribs, the <a href="/wiki/External_intercostal_muscle" class="mw-redirect" title="External intercostal muscle">external intercostals</a>, assist with this process. </p> <div class="mw-heading mw-heading3"><h3 id="Defences_against_infection">Defences against infection</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=7" title="Edit section: Defences against infection"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="/wiki/Mucociliary_clearance" title="Mucociliary clearance">Mucociliary clearance</a></div> <p>The epithelial lining of the upper respiratory tract is interspersed with <a href="/wiki/Goblet_cell" title="Goblet cell">goblet cells</a> that secrete a protective <a href="/wiki/Mucus" title="Mucus">mucus</a>. This helps to filter waste, which is eventually either swallowed into the highly acidic stomach environment or expelled via spitting. The epithelium lining the respiratory tract is covered in small hairs called <a href="/wiki/Cilia" class="mw-redirect" title="Cilia">cilia</a>. These beat rhythmically out from the lungs, moving secreted mucus foreign particles toward the <a href="/wiki/Laryngopharynx" class="mw-redirect" title="Laryngopharynx">laryngopharynx</a> upwards and outwards, in a process called <a href="/wiki/Mucociliary_clearance" title="Mucociliary clearance">mucociliary clearance</a>, preventing mucus accumulation in the lungs. <a href="/wiki/Macrophage" title="Macrophage">Macrophages</a> in the alveoli are part of the immune system which <a href="/wiki/Phagocytosis" title="Phagocytosis">engulf</a> and digest any inhaled harmful agents. </p><p>Hair in the nostrils plays a protective role, trapping particulate matter such as dust.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> These hairs, called vibrissae, are thicker than body hair and effectively block larger particles from entering the respiratory tract. They also increase the surface area for particle deposition, improving the nose's ability to filter pathogens. <sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/Cough_reflex" title="Cough reflex">cough reflex</a> expels all irritants within the mucous membrane to the outside. The airways of the lungs contain rings of muscle. When the passageways are irritated by some allergen, these muscles can constrict. </p> <div class="mw-heading mw-heading2"><h2 id="Clinical_significance">Clinical significance</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=8" title="Edit section: Clinical significance"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Respiratory_disease" title="Respiratory disease">Respiratory disease</a></div> <p>The respiratory tract is a common site for infections. </p> <div class="mw-heading mw-heading3"><h3 id="Infection">Infection</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=9" title="Edit section: Infection"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading4"><h4 id="Upper_respiratory_infection">Upper respiratory infection</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=10" title="Edit section: Upper respiratory infection"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Upper_respiratory_tract_infection" title="Upper respiratory tract infection">Upper respiratory tract infection</a></div> <p><a href="/wiki/Upper_respiratory_tract_infection" title="Upper respiratory tract infection">Upper respiratory tract infections</a> are probably the most common infections in the world. </p><p>The respiratory system is very prone to developing infections in the lungs. Infants and older adults are more likely to develop infections in their lungs because their lungs are not as strong in fighting off these infections. Most of these infections used to be fatal, but with new research and medicine, they are now treatable. With bacterial infections, antibiotics are prescribed, while viral infections are harder to treat but still curable. </p><p>The <a href="/wiki/Common_cold" title="Common cold">common cold</a>, and <a href="/wiki/Influenza" title="Influenza">flu</a> are the most common causes of an upper respiratory tract infection, which can cause more serious illness that can develop in the lower respiratory tract. </p> <div class="mw-heading mw-heading4"><h4 id="Lower_respiratory_tract_infections">Lower respiratory tract infections</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=11" title="Edit section: Lower respiratory tract infections"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Main articles: <a href="/wiki/Lower_respiratory_infection" class="mw-redirect" title="Lower respiratory infection">Lower respiratory infection</a> and <a href="/wiki/Pneumonia" title="Pneumonia">Pneumonia</a></div> <p><a href="/wiki/Pneumonia" title="Pneumonia">Pneumonia</a> is the most common, and frequent <a href="/wiki/Lower_respiratory_tract_infection" title="Lower respiratory tract infection">lower respiratory tract infection</a>. This can be either viral, bacterial, or fungal. This infection is very common because pneumonia can be airborne, and when you inhale this infection in the air, the particles enter the lungs and move into the air sacs. This infection quickly develops in the lower part of the lung and fills the lung with fluid, and excess mucus. This causes difficulty in breathing and coughing as the lower respiratory tract tries to get rid of the fluid in the lungs. You can be more prone to developing this infection if you have asthma, flu, heart disease, or cancer<sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p><p> <a href="/wiki/Bronchitis" title="Bronchitis">Bronchitis</a> is another common infection that takes place in the lower respiratory tract. It is an inflammation of the bronchial tubes. There are two forms of this infection: acute bronchitis, which is treatable and can go away without treatment, or chronic bronchitis, which comes and goes, but will always affect one's lungs. Bronchitis increases the amount of mucus that is natural in your respiratory tract. Chronic bronchitis is common in smokers, because the tar from smoking accumulates over time, causing the lungs to work harder to repair themselves.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> </p><p> <a href="/wiki/Tuberculosis" title="Tuberculosis">Tuberculosis</a> is one of many other infections that occurs in the lower respiratory tract. You can contract this infection from airborne droplets, and if inhaled you are at risk of this disease. This is a bacterial infection that deteriorates the lung tissue resulting in coughing up blood.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> This infection is deadly if not treated. </p> <div class="mw-heading mw-heading3"><h3 id="Cancer">Cancer</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=12" title="Edit section: Cancer"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Lung_cancer" title="Lung cancer">Lung cancer</a></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Respiratory_Tract.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Respiratory_Tract.jpg/233px-Respiratory_Tract.jpg" decoding="async" width="233" height="131" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Respiratory_Tract.jpg/350px-Respiratory_Tract.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Respiratory_Tract.jpg/466px-Respiratory_Tract.jpg 2x" data-file-width="1920" data-file-height="1080" /></a><figcaption>3D still showing increased mucus</figcaption></figure> <p>Some of these <a href="/wiki/Cancer" title="Cancer">cancers</a> have environmental causes such as smoking. When a tobacco product is inhaled, the smoke paralyzes the cilia, causing mucus to enter the lungs. Frequent smoking, over time, causes the cilia hairs to die and can no longer filter mucus. Tar from the smoke inhaled enters the lungs, turning the pink-coloured lungs black. The accumulation of this tar could eventually lead to <a href="/wiki/Lung_cancer" title="Lung cancer">lung cancer</a>, or <a href="/wiki/Chronic_obstructive_pulmonary_disease" title="Chronic obstructive pulmonary disease">chronic obstructive pulmonary disease</a>.<sup id="cite_ref-medscape_7-1" class="reference"><a href="#cite_note-medscape-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="COPD">COPD</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=13" title="Edit section: COPD"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Chronic_obstructive_pulmonary_disease" title="Chronic obstructive pulmonary disease">Chronic obstructive pulmonary disease</a></div> <p><a href="/wiki/Chronic_obstructive_pulmonary_disease" title="Chronic obstructive pulmonary disease">Chronic obstructive pulmonary disease</a> (COPD) is a common lower respiratory disease that can be caused by exposure to harmful chemicals, or prolonged use of tobacco. This disease is chronic and progressive, the damage to the lungs is irreversible and eventually fatal. COPD destroys the alveoli, and lung tissue which makes breathing very difficult, causing <a href="/wiki/Shortness_of_breath" title="Shortness of breath">shortness of breath</a>, <a href="/wiki/Hyperventilation" title="Hyperventilation">hyperventilation</a>, and raised chest. The decreased number of alveoli causes loss of oxygen supply to the lungs and an increased accumulation of carbon dioxide. There are two types of COPD: primary and secondary.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (July 2020)">citation needed</span></a></i>]</sup> Primary COPD can be found in younger adults. This type of COPD deteriorates the air sacs, and lung mass. Secondary COPD can be found in older adults who smoke or have smoked and have a history of bronchitis. <sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (July 2020)">citation needed</span></a></i>]</sup> COPD includes symptoms of <a href="/wiki/Pneumatosis#Lungs" title="Pneumatosis">emphysema</a> and <a href="/wiki/Bronchitis#Chronic_bronchitis" title="Bronchitis">chronic bronchitis</a>.<sup id="cite_ref-Medscape2019_19-0" class="reference"><a href="#cite_note-Medscape2019-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Asthma">Asthma</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=14" title="Edit section: Asthma"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Asthma" title="Asthma">Asthma</a></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Respiratory_tract.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/61/Respiratory_tract.jpg/236px-Respiratory_tract.jpg" decoding="async" width="236" height="133" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/61/Respiratory_tract.jpg/354px-Respiratory_tract.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/61/Respiratory_tract.jpg/472px-Respiratory_tract.jpg 2x" data-file-width="1920" data-file-height="1080" /></a><figcaption>3D still showing constricted airways</figcaption></figure> <p>The bronchi are the main passages to the right and left lungs. These airways carry oxygen to the bronchioles inside the lungs. <a href="/wiki/Inflammation" title="Inflammation">Inflammation</a> of the bronchii and bronchioles can cause them to swell up, which could lead to an <a href="/wiki/Asthma" title="Asthma">asthma</a> attack. This results in <a href="/wiki/Wheeze" title="Wheeze">wheezing</a>, tightness of the chest, and severe difficulty in breathing. There are different types of asthma that affect the functions of the bronchial tubes. Allergies can also set off an allergic reaction, causing swelling of the bronchial tubes; as a result, the air passage will swell up, or close up completely.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Mouth_breathing">Mouth breathing</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=15" title="Edit section: Mouth breathing"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In general, air is inhaled <a href="/wiki/Obligate_nasal_breathing" title="Obligate nasal breathing">through the nose</a>. It can be inhaled through the mouth if it is not possible to breathe through the nose. However, chronic <a href="/wiki/Mouth_breathing" title="Mouth breathing">mouth breathing</a> can cause a dry mouth and lead to infections.<sup id="cite_ref-guardian_21-0" class="reference"><a href="#cite_note-guardian-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=16" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Airway_tone" title="Airway tone">Airway tone</a></li> <li><a href="/wiki/Jet_ventilation" class="mw-redirect" title="Jet ventilation">Jet ventilation</a></li> <li><a href="/wiki/Nasopharyngeal_airway" title="Nasopharyngeal airway">Nasopharyngeal airway</a></li> <li><a href="/wiki/Oropharyngeal_airway" title="Oropharyngeal airway">Oropharyngeal airway</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Respiratory_tract&action=edit&section=17" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-Patwa-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-Patwa_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Patwa_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFPatwaShah2015" class="citation journal cs1">Patwa A, Shah A (September 2015). <a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4613399">"Anatomy and physiology of respiratory system relevant to anaesthesia"</a>. <i>Indian Journal of Anaesthesia</i>. <b>59</b> (9): <span class="nowrap">533–</span>541. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.4103%2F0019-5049.165849">10.4103/0019-5049.165849</a></span>. <a href="/wiki/PMC_(identifier)" class="mw-redirect" title="PMC (identifier)">PMC</a> <span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4613399">4613399</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/26556911">26556911</a>.</cite><span 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talk:Lower respiratory system anatomy"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Lower_respiratory_system_anatomy" title="Special:EditPage/Template:Lower respiratory system anatomy"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Anatomy_of_the_lower_respiratory_tract135" style="font-size:114%;margin:0 4em">Anatomy of the <a class="mw-selflink selflink">lower respiratory tract</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a class="mw-selflink-fragment" href="#Respiratory_tree">Respiratory tree</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Trachea" title="Trachea">Trachea</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Tracheal_rings" class="mw-redirect" title="Tracheal rings">Tracheal rings</a></li> <li><a href="/wiki/Trachea" title="Trachea">Annular ligaments</a></li> <li><a href="/wiki/Carina_of_trachea" title="Carina of trachea">Carina</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Bronchus" title="Bronchus">Bronchi</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li>Main <ul><li><a href="/wiki/Bronchus#Structure" title="Bronchus">left</a></li> <li><a href="/wiki/Bronchus" title="Bronchus">right</a></li></ul></li> <li><a href="/wiki/Bronchus" title="Bronchus">Secondary</a> <ul><li><a href="/wiki/Eparterial_bronchus" title="Eparterial bronchus">eparterial</a></li></ul></li> <li><a href="/wiki/Bronchus#Structure" title="Bronchus">Tertiary</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Human_lung" class="mw-redirect" title="Human lung">Lungs</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%">General</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li>Landmarks <ul><li><a href="/wiki/Base_of_lung" class="mw-redirect" title="Base of lung">Base</a></li> <li><a href="/wiki/Apex_of_lung" class="mw-redirect" title="Apex of lung">Apex</a></li> <li><a href="/wiki/Root_of_the_lung" title="Root of the lung">Root</a></li> <li><a href="/wiki/Hilum_of_lung" class="mw-redirect" title="Hilum of lung">Hilum</a></li></ul></li> <li>Fissures <ul><li><a href="/wiki/Horizontal_fissure_of_right_lung" class="mw-redirect" title="Horizontal fissure of right lung">Horizontal</a></li> <li><a href="/wiki/Oblique_fissure" class="mw-redirect" title="Oblique fissure">Oblique</a></li></ul></li> <li><a href="/wiki/Superior_lobe" class="mw-redirect" title="Superior lobe">Superior lobe</a></li> <li><a href="/wiki/Lingula_of_left_lung" class="mw-redirect" title="Lingula of left lung">Lingula of left lung</a></li> <li><a href="/wiki/Middle_lobe_of_right_lung" class="mw-redirect" title="Middle lobe of right lung">Middle lobe of right lung</a></li> <li><a href="/wiki/Left_lung#Lobes" class="mw-redirect" title="Left lung">Inferior lobe</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Bronchopulmonary_segment" title="Bronchopulmonary segment">BP segment</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Bronchiole" title="Bronchiole">Bronchiole</a>: <a href="/wiki/Conducting_zone" class="mw-redirect" title="Conducting zone">Conducting zone</a> (<a href="/wiki/Terminal_bronchiole" class="mw-redirect" title="Terminal bronchiole">Terminal bronchiole</a>)</li> <li><a href="/wiki/Respiratory_zone" class="mw-redirect" title="Respiratory zone">Respiratory zone</a> (<a href="/wiki/Respiratory_bronchiole" class="mw-redirect" title="Respiratory bronchiole">Respiratory bronchiole</a></li> <li><a href="/wiki/Alveolar_duct" class="mw-redirect" title="Alveolar duct">Alveolar duct</a></li> <li><a href="/wiki/Pulmonary_alveolus" title="Pulmonary alveolus">Alveolus</a></li> <li><a href="/wiki/Blood-air_barrier" class="mw-redirect" title="Blood-air barrier">Blood-air barrier</a>)</li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Cells</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Alveolar_cells" class="mw-redirect" title="Alveolar cells">Alveolar cells</a> <ul><li><a href="/wiki/Alveolar_cells" class="mw-redirect" title="Alveolar cells">Type I</a></li> <li><a href="/wiki/Alveolar_cells" class="mw-redirect" title="Alveolar cells">Type II</a></li></ul></li> <li><a href="/wiki/Club_cell" title="Club cell">Club cell</a></li> <li><a href="/wiki/Goblet_cell" title="Goblet cell">Goblet cell</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374" /><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235" /></div><div role="navigation" class="navbox" aria-labelledby="Respiratory_physiology123" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374" /><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231" /><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Respiratory_physiology" title="Template:Respiratory physiology"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Respiratory_physiology" title="Template talk:Respiratory physiology"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Respiratory_physiology" title="Special:EditPage/Template:Respiratory physiology"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Respiratory_physiology123" style="font-size:114%;margin:0 4em"><a href="/wiki/Respiratory_physiology" class="mw-redirect" title="Respiratory physiology">Respiratory physiology</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Respiration</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Breath" class="mw-redirect" title="Breath">breath</a> <ul><li><a href="/wiki/Inhalation" title="Inhalation">inhalation</a></li> <li><a href="/wiki/Exhalation" title="Exhalation">exhalation</a></li> <li><a href="/wiki/Obligate_nasal_breathing" title="Obligate nasal breathing">obligate nasal breathing</a></li></ul></li> <li><a href="/wiki/Respiratory_rate" title="Respiratory rate">respiratory rate</a></li> <li><a href="/wiki/Respirometer" title="Respirometer">respirometer</a></li> <li><a href="/wiki/Pulmonary_surfactant" title="Pulmonary surfactant">pulmonary surfactant</a></li> <li><a href="/wiki/Pulmonary_compliance" class="mw-redirect" title="Pulmonary compliance">compliance</a></li> <li><a href="/wiki/Elastic_recoil" title="Elastic recoil">elastic recoil</a></li> <li><a href="/wiki/Hysteresivity" title="Hysteresivity">hysteresivity</a></li> <li><a href="/wiki/Airway_resistance" title="Airway resistance">airway resistance</a></li> <li>bronchial <ul><li><a href="/wiki/Bronchial_hyperresponsiveness" title="Bronchial hyperresponsiveness">hyperresponsiveness</a></li> <li><a href="/wiki/Bronchoconstriction" title="Bronchoconstriction">constriction</a></li> <li><a href="/wiki/Bronchodilatation" title="Bronchodilatation">dilatation</a></li></ul></li> <li><a href="/wiki/Mechanical_ventilation" title="Mechanical ventilation">mechanical ventilation</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Control_of_ventilation" title="Control of ventilation">Control</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><i><a href="/wiki/Pons" title="Pons">pons</a></i> <ul><li><a href="/wiki/Pneumotaxic_center" class="mw-redirect" title="Pneumotaxic center">pneumotaxic center</a></li> <li><a href="/wiki/Apneustic_center" class="mw-redirect" title="Apneustic center">apneustic center</a></li></ul></li> <li><i><a href="/wiki/Medulla_oblongata" title="Medulla oblongata">medulla</a></i> <ul><li><a href="/wiki/Dorsal_respiratory_group" class="mw-redirect" title="Dorsal respiratory group">dorsal respiratory group</a></li> <li><a href="/wiki/Ventral_respiratory_group" class="mw-redirect" title="Ventral respiratory group">ventral respiratory group</a></li></ul></li> <li><i><a href="/wiki/Chemoreceptor" title="Chemoreceptor">chemoreceptors</a></i> <ul><li><a href="/wiki/Central_chemoreceptor" title="Central chemoreceptor">central</a></li> <li><a href="/wiki/Peripheral_chemoreceptor" title="Peripheral chemoreceptor">peripheral</a></li></ul></li> <li><a href="/wiki/Pulmonary_stretch_receptor" title="Pulmonary stretch receptor">pulmonary stretch receptor</a> <ul><li><a href="/wiki/Hering%E2%80%93Breuer_reflex" title="Hering–Breuer reflex">Hering–Breuer reflex</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Lung_volumes" class="mw-redirect" title="Lung volumes">Lung volumes</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Vital_capacity" title="Vital capacity">VC</a></li> <li><a href="/wiki/Functional_residual_capacity" title="Functional residual capacity">FRC</a></li> <li><a href="/wiki/Tidal_volume" title="Tidal volume">Vt</a></li> <li><a href="/wiki/Dead_space_(physiology)" title="Dead space (physiology)">dead space</a></li> <li><a href="/wiki/Closing_capacity" title="Closing capacity">CC</a></li> <li><a href="/wiki/Peak_expiratory_flow" title="Peak expiratory flow">PEF</a></li></ul> <dl><dt>calculations</dt> <dd></dd> <dd><a href="/wiki/Respiratory_minute_volume" class="mw-redirect" title="Respiratory minute volume">respiratory minute volume</a></dd> <dd><a href="/wiki/FEV1/FVC_ratio" title="FEV1/FVC ratio">FEV1/FVC ratio</a></dd></dl> <dl><dt><a href="/wiki/Lung_function_test" class="mw-redirect" title="Lung function test">Lung function tests</a></dt> <dd></dd> <dd><a href="/wiki/Spirometry" title="Spirometry">spirometry</a></dd> <dd><a href="/wiki/Body_plethysmography" class="mw-redirect" title="Body plethysmography">body plethysmography</a></dd> <dd><a href="/wiki/Peak_flow_meter" class="mw-redirect" title="Peak flow meter">peak flow meter</a></dd> <dd><a href="/wiki/Nitrogen_washout" title="Nitrogen washout">nitrogen washout</a></dd></dl> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Circulation</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Pulmonary_circulation" title="Pulmonary circulation">pulmonary circulation</a></li> <li><a href="/wiki/Hypoxic_pulmonary_vasoconstriction" title="Hypoxic pulmonary vasoconstriction">hypoxic pulmonary vasoconstriction</a></li> <li><a href="/wiki/Pulmonary_shunt" title="Pulmonary shunt">pulmonary shunt</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Interactions</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ventilation_(physiology)" class="mw-redirect" title="Ventilation (physiology)">ventilation (V)</a></li> <li><a href="/wiki/Perfusion" title="Perfusion">Perfusion</a> (Q) <ul><li><a href="/wiki/Ventilation/perfusion_ratio" title="Ventilation/perfusion ratio">Ventilation/perfusion ratio</a></li> <li><a href="/wiki/Ventilation/perfusion_scan" title="Ventilation/perfusion scan">V/Q scan</a></li></ul></li> <li><a href="/wiki/Zones_of_the_lung" title="Zones of the lung">zones of the lung</a></li> <li><a href="/wiki/Gas_exchange" title="Gas exchange">gas exchange</a></li> <li><a href="/wiki/Pulmonary_gas_pressures" title="Pulmonary gas pressures">pulmonary gas pressures</a></li> <li><a href="/wiki/Alveolar_gas_equation" title="Alveolar gas equation">alveolar gas equation</a></li> <li><a href="/wiki/Alveolar%E2%80%93arterial_gradient" title="Alveolar–arterial gradient">alveolar–arterial gradient</a></li> <li><a href="/wiki/Hemoglobin" title="Hemoglobin">hemoglobin</a></li> <li><a href="/wiki/Oxygen%E2%80%93hemoglobin_dissociation_curve" title="Oxygen–hemoglobin dissociation curve">oxygen–hemoglobin dissociation curve</a> (<a href="/wiki/Oxygen_saturation" title="Oxygen saturation">Oxygen saturation</a></li> <li><a href="/wiki/2,3-Bisphosphoglyceric_acid" title="2,3-Bisphosphoglyceric acid">2,3-BPG</a></li> <li><a href="/wiki/Bohr_effect" title="Bohr effect">Bohr effect</a></li> <li><a href="/wiki/Haldane_effect" title="Haldane effect">Haldane effect</a>)</li> <li><a href="/wiki/Carbonic_anhydrase" title="Carbonic anhydrase">carbonic anhydrase</a> (<a href="/wiki/Chloride_shift" title="Chloride shift">chloride shift</a>)</li> <li><a href="/wiki/Oxyhemoglobin" class="mw-redirect" title="Oxyhemoglobin">oxyhemoglobin</a></li> <li><a href="/wiki/Respiratory_quotient" title="Respiratory quotient">respiratory quotient</a></li> <li><a href="/wiki/Arterial_blood_gas" class="mw-redirect" title="Arterial blood gas">arterial blood gas</a></li> <li><a href="/wiki/Diffusion_capacity" class="mw-redirect" title="Diffusion capacity">diffusion capacity</a> (<a href="/wiki/DLCO" class="mw-redirect" title="DLCO">DLCO</a>)</li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Insufficiency</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Effects_of_high_altitude_on_humans" title="Effects of high altitude on humans">high altitude</a> <ul><li><a href="/wiki/Death_zone" title="Death zone">death zone</a></li></ul></li> <li><a href="/wiki/Oxygen_toxicity" title="Oxygen toxicity">oxygen toxicity</a></li> <li><a href="/wiki/Hypoxia_(medical)" class="mw-redirect" title="Hypoxia (medical)">hypoxia</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374" /><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235" /><style data-mw-deduplicate="TemplateStyles:r1038841319">.mw-parser-output .tooltip-dotted{border-bottom:1px dotted;cursor:help}</style></div><div role="navigation" class="navbox authority-control" aria-label="Navbox601" style="padding:3px"><table class="nowraplinks hlist navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Help:Authority_control" title="Help:Authority control">Authority control databases</a>: National 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