医学专业英语 Chapter 5 Respiratory System教案资料Word文档下载推荐.docx
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RespiratorySystem
Inthispassageyouwilllearn:
●Theorgansoftherespiratorysystem
●Thestructureandfunctionoftheseorgans
●Themechanismofbreathing
●Thegastransportandcleaningsystem
Alllivinganimalsmusttakeinoxygenandgetridofcarbondioxide.Inthevertebrates——animalswithbackbones——thatgettheiroxygenfromtheair,bothtasksareperformedbyspecialgas-exchangeorganscalledlungs.Thelungsprovideaplacewhereoxygencanreachthebloodandcarbondioxidecanberemovedfromit.Theyareequippedwithtubesandabellowssystemfordrawinginairfromtheoutside,whilethepulmonaryveinsandarteriescirculatebloodthroughfrominside.Thelungsalsohaveacleaningsystemthattraps,ejects,ordestroysirritantsandotherharmfulsubstancesthattravelinwiththeair.
Inthesimplercold-bloodedamphibiansandreptiles,thelungsaretwoballoon-likesacs.Inactiveanimalsthatrequirelargeamountsofoxygen,especiallythewarm-bloodedbirdsandmammals,thelungsareaspongylabyrinthofsacsthatsupplyanenormoussurfaceareaforthetransferofgases.Intheadulthumanthetotallungsurface,ifflattenedout,wouldbelargerthanabadmintoncourt,about100squareyards(83squaremeters).
Airentersthebodythroughthenoseandpassesthroughthenasalcavity,whichislinedwithamucousmembraneandfinehairs(cilia)tohelpfilteroutforeignbodies,aswellastowarmand
moistentheair.Paranasalsinusesarehollow,air-containingspaceswithintheskullthatcommunicatewiththenasalcavity.They,too,haveamucousmembraneliningandfunctiontoprovidethelubricatingfluidmucus.aswellastolightenthebonesoftheskullandhelpproducesound.
Afterpassingthroughthenasalcavity,theairnextreachesthepharynx(throat).Thereare
threedivisionsofthepharynx.Thenasopharynxisthefirstdivision,anditisnearesttothenasal
cavities.Itcontainstheadenoids,whicharemassesoflymphatictissue.Theadenoids(alsoknownasthepharyngealtonsils)aremoreprominentinchildren,andifenlarged,theycanobstructairpassageways.Belowthenasopharynxandclosertothemouthistheseconddivisionofthepharynx,theoropharynx.Thepalatinetonsils,tworoundedmassedoflymphatictissue,arelocatedintheoropharynx.Thethirddivisionofthepharynxisthehypopharynx(alsocalledthelaryngopharynx).
Itisinthehypopharyngealregionthatthepharynx,servingasacommonpassagewayforfoodfromthemouthandairfromthenose,dividesintotwobranches,thelarynx(voicebox)andtheesophagus.
Theesophagusleadsintothestomachandcarriesfoodtobedigested.Thelarynxcontainsthevocalcordsandissurroundedbypiecesofcartilageforsupport.Soundsareproducedasairisexpelledpastthevocalcords,andthecordsvibrate.Thetensionofthevocalcordsdeterminesthehighorlowpitchofthevoice.
Sincefoodenteringfromthemouthandairenteringfromthenosemixinthepharynx,whatpreventsthepassingoffoodordrinkintothelarynxandrespiratorysystemafterithasbeenswallowed?
Evenwithasmallquantityofsolidorliquidmatterfindingitswayintotheairpassages,breathingcouldbeseriouslyblocked.Aspecialdeterrenttothiseventisprovidedforbyaflapofcartilageattachedtotherootofthetonguethatactslikealidoverthelarynx.Thisflapofcartilageiscalledtheepiglottis.Theepiglottisliesovertheentrancetothelarynx.Intheactofswallowing,whenfoodandliquidmovethroughthethroat,theepiglottisclosesoffthelarynx,sothatthesethingscannotenter.
Onitswaytothelungs,airpassesfromthelarynxtothetrachea(windpipe),averticaltube
about4
incheslongand1inchindiameter.Thetracheaiskeptopenby16-20C-shapedringsofcartilageseparatedbyfibrousconnectivetissuethatstiffensthefrontandsidesofthetube.Intheregionofthemediastinum,thetracheadividesintotwobranchescalledbronchi.Eachbronchusleadstoaseparatelunganddividesandsubdividesintosmallerandfinertubes,somewhatlikethebranchesofatree(seeFigure6-1).
Diaphragm
Figure6-1
Thesmallestofthebronchialbranchesarecalledbronchioles.Attheendofthebronchiolesareclustersofairsacscalledalveoli.Eachalveolusismadeofaone-celllayerofepithelium.Theverythinwallallowsfortheexchangeofgasesbetweenthealveolusandthecapillariesthatsurroundandcomeinclosecontactwithit.Thebloodthatflowsthroughthecapillariesacceptstheoxygenfromthealveolusanddepositscarbondioxideintothealveolustobeexhaled.Oxygeniscombinedwithahemoglobininerythrocytesandcarriedtoallpartsofthebody.
Eachlungisenvelopedinadouble-foldedmembranecalledthepleura.Theouterlayerofthepleura,nearest