医学专业英语 Chapter 5 Respiratory System教案资料Word文档下载推荐.docx

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