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Therespiratorysystemcanbedividedintotwoparts:Theupperrespiratorytracts:mouth,nose&nasalcavity,pharynxandlarynxThelowerrespiratorytracts:trachea,bronchi,bronchioles,alveoli,diaphragmandlungsFunctionTransportsairintothelungsandfacilitatesthediffusionofoxygenintothebloodstream.Italsoreceiveswastecarbondioxidefromthebloodandexhalesit.Mouth,nose&nasalcavity:Thefunctionofthispartofthesystemistowarm,filterandmoistentheincomingair.Pharynx:Herethethroatdividesintothetrachea(windpipe)andesophagus(foodpipe).Thereisalsoasmallflapofcartilagecalledtheepiglottiswhichpreventsfoodfromenteringthetrachea.Larynx:Thisisalsoknownasthevoiceboxasitiswheresoundisgenerated.Itcontainsthevocalcords.Italsohelpsprotectthetracheabyproducingastrongcoughreflexifanysolidobjectspasstheepiglottis.TheUpperRespiratoryTractsTracheaMuscularcartilaginoustractthatisacontinuationofthelarynx;itdividesintotwomainbronchi,eachofwhichendsinalung,andallowsairtopass.Theinnermembraneofthetracheaiscoveredintinyhairscalledcilia,whichcatchparticlesofdustwhichwecanthenremovethroughcoughing.BronchiThetracheadividesintotwotubescalledbronchi,oneenteringtheleftandoneenteringtherightlung.Bronchibranchintosmallerandsmallertubesknownasbronchioles.Bronchiolesterminateingrape-likesacclustersknownasalveoli.Alveoliaresurroundedbyanetworkofthin-walledcapillaries.Bronchioles:Tertiarybronchicontinuetodivideandbecomebronchioles,verynarrowtubes.Thereisnocartilagewithinthebronchiolesandtheyleadtoalveolarsacs.Alveoli:Individualhollowcavitiescontainedwithinalveolarsacs(orducts).Alveolihaveverythinwallswhichpermittheexchangeofgasesoxygenandcarbondioxide.Theyaresurroundedbyanetworkofcapillaries,intowhichtheinspiredgasespass.Thereareapproximately3millionalveoliwithinanaverageadultlung.TheLowerRespiratoryTractsThelungstakeinoxygen,whichallcellsthroughoutthebodyneedtoliveandcarryouttheirnormalfunctions.Thelungsalsogetridofcarbondioxide,awasteproductofthebody'scells.Thelungsareapairofcone-shapedorgansmadeupofspongy,pinkish-graytissue.Theytakeupmostofthespaceinthechest,orthethorax(thepartofthebodybetweenthebaseoftheneckanddiaphragm).Thelungsareseparatedfromeachotherbythemediastinum,anareathatcontainsthefollowing:heartanditslargevesselstrachea(windpipe)esophagusthymuslymphnodesTherightlunghasthreesections,calledlobes.Theleftlunghastwolobes.Whenyoubreathe,theair:entersthebodythroughthenoseorthemouthtravelsdownthethroatthroughthelarynx(voicebox)andtrachea(windpipe)goesintothelungsthroughtubescalledmain-stembronchionemain-stembronchusleadstotherightlungandonetotheleftlunginthelungs,themain-stembronchidivideintosmallerbronchiandthenintoevensmallertubescalledbronchiolesbronchiolesendintinyairsacscalledalveoliDiaphragmlocatedbelowthelungs,attachingtothelowerribs,sternumandlumbarspineandformingthebaseofthethoraciccavity,isthemajormuscleofrespiration.Itisalarge,dome-shapedmusclethatcontractsrhythmicallyandcontinually,andmostofthetime,involuntarily.Uponinhalation,thediaphragmcontractsandflattensandthechestcavityenlarges.Thiscontractioncreatesavacuum,whichpullsairintothelungs.Uponexhalation,thediaphragmrelaxesandreturnstoitsdomelikeshape,andairisforcedoutofthelungs.