医学专业英语 Chapter 5 Respiratory System.docx

医学专业英语 Chapter 5 Respiratory System.docx

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医学专业英语Chapter5RespiratorySystem

医学专业英语Chapter5RespiratorySystem

Chapter5RespiratorySystemInthispassageyouwilllearn:

●Theorgansoftherespiratorysystem●Thestructureandfunctionoftheseorgans●Themechanismofbreathing●ThegastransportandcleaningsystemAlllivinganimalsmusttakeinoxygenandgetridofcarbondioxide.Inthevertebratesanimalswithbackbonesthatgettheiroxygenfromtheair,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,aswellastowarmandmoistentheair.Paranasalsinusesarehollow,air-containingspaceswithintheskullthatcommunicatewiththenasalcavity.They,too,haveamucousmembraneliningandfunctiontoprovidethelubricatingfluidmucus.aswellastolightenthebonesoftheskullandhelpproducesound.Afterpassingthroughthenasalcavity,theairnextreachesthepharynx（throat）.Therearethreedivisionsofthepharynx.Thenasopharynxisthefirstdivision,anditisnearesttothenasalcavities.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）,averticaltubeabout421incheslongand1inchindiameter.Thetracheaiskeptopenby16-20C-shapedringsofcartilageseparatedbyfibrousconnectivetissuethatstiffensthefrontandsidesofthetube.Intheregionofthemediastinum,thetracheadividesintotwobranchescalledbronchi.Eachbronchusleadstoaseparatelunganddividesandsubdividesintosmallerandfinertubes,somewhatlikethebranchesofatree（seeFigure6-1）.DiaphragmFigure6-1Thesmallestofthebronchialbranchesarecalledbronchioles.Attheendofthebronchiolesareclustersofairsacscalledalveoli.Eachalveolusismadeofaone-celllayerofepithelium.Theverythinwallallowsfortheexchangeofgasesbetweenthealveolusandthecapillariesthatsurroundandcomeinclosecontactwithit.Thebloodthatflowsthroughthecapillariesacceptstheoxygenfromthealveolusanddepositscarbondioxideintothealveolustobeexhaled.Oxygeniscombinedwithahemoglobininerythrocytesandcarriedtoallpartsofthebody.Eachlungisenvelopedinadouble-foldedmembranecalledthepleura.Theouterlayerofthepleura,nearesttheribs,istheparietalpleura,andtheinnerlayer,closesttothelung,isthevisceralpleura.Thepleuraismoistenedwithaseroussecretionthatfacilitatesthemovementsofthelungswithinthethorax.Thetwolungsarenotquitemirrorimagesofeachother.Therightlung,whichistheslightlylargerofthetwo,isdividedintothreelobes,ordivisions,andtheleftlungisdividedintotwolobes.Itispossibleforonelobeofthelungtoberemovedwithoutdamagetotherest,whichcancontinuetofunctionnormally;Theuppermostpartofthelungiscalledtheapex,andthelowerareaisthebase.Thehilumofthelungisthemidlineregionwherebloodvessels,nerves,andbronchialtubesenterandexittheorgan.Thelungsextendfromthecollarbonetothediaphragminthethoraciccavity.Thediaphragmisamuscularpartitionthatseparatesthethoracicfromtheabdominalcavityandaidsintheprocessofbreathing.Thediaphragmcontractsanddescendswitheachinhalation（inspiration）.Thedownwardmovementofthediaphragmenlargestheareainthethoraciccavityandreducestheinternalairpressure,sothatairflowsintothelungstoequalizethepressure.Whenthelungsarefull,thediaphragmrelaxesandelevates,makingtheareainthethoraciccavitysmaller,andthusincreasingtheairpressureinthethorax.Airthenisexpelledoutofthelungstoequalizethepressure;thisiscalledexhalation（expiration）.Otherpartsarealsoinvolvedintheprocess.Thecycleofrespirationreallybeginswhenthephrenicnervestimulatesthediaphragmtocontractandflatten.Also,theintercostalmusclesbetweentheribsaidininspirationbypullingtheribsupandout.Themeasureofhoweasilythelungsexpandunderpressureiscompliance.Breathingisregulatedunconsciouslybycenterinthebrainstem.Thesecentersadjusttherateandrhythmofbreathingaccordingtochangesinthecompositionoftheblood,especiallytheconcentrationofcarbondioxide.GasTransport.Oxygeniscarriedinthebloodboundtohemoglobininredbloodcells.Theoxygenisreleasedtothecellsasneeded.Carbondioxideiscarriedinseveralways,butismostlyconvertedtoanacidcalledcarbonicacid.Theamountofcarbondioxidethatisexhaledisimportantinregulatingtheacidityoralkalinityoftheblood.Iftoomuchcarbondioxideisexhaledbyhyperventilation,bodyfluidstendtobecomemorealkaline,aconditiontermedalkalosis.Iftoolittlecarbondioxideisexhaledasaresultofhypoventilation,bodyfluidstendtobecomemoreacid,aconditiontermedacidosis.Thecleaningsystemofthelungshasfourmaincomponents.Liningthetracheaandbronchialtreearecellsthatsecretemucus,whichtrapspollutantsandbacteria.Alsointhebronchiarecellscontainingtinycilia,thatprojectintotheblanketofmucusandwithconstantwavelikemotionspushthemucusupoutoftheairways.Irritatingchemicals,stagnantandexcessivemucus,andlargebitsofforeignmatterareforciblyejectedassputumfromthebronchibyacough.Thisthirdimportantcleaningdevicelikebreathing,underpartialvoluntarycontrolisarapidmusclecontractionandbronchial-tubeconstrictionthatgeneratesawindforcefarstrongerthanatornado.Smallharmfulsubstancesthatmaketheirwayintothealveoliaredestroyedbythefourthlineofdefense,themacrophages.Thesearepatrollingcellsthatswallowupforeignparticlesordestroythemwithenzymes.NewWordsandPhrasesExercisesA.Discussthefollowingtopics:

1.Imagineyouwerelecturinginfrontofruralhealthworkersonthetopicofrespiratorysystem,drawapicturetoillustratethewholesystem.2.Describetheirstructuresandfunctions.3.Howcanepiglottispreventthepassingfoodanddrinkintotherespiratorysystem?

4.Whatroledoesthediaphragmplayintheprocessofbreathing?

5.Whatarethefourcomponentsofthecleaningsystem?

Howdotheyfunction?

B.Fillintheblankswiththewordsgivenbelowandchangetheirformsifnecessary.alveoluscapillarydiaphragmhemoglobinthoraciccavitygasexchangeparietalpleuravisceralpleuramediastinumpleuralspaceThelungsaretwocone-shaped,spongyorgansconsistingofalveoli,bloodvessels,elastictissueandnerves.Eachofthetwolungsconsistsofsmallerdivisionscalledlobes;theleftlunghastwolobes,whiletherightlungisdividedintothreelobes.Inthelungs,

（1）aresurroundedbyanetworkoftinybloodvesselscalledcapillaries;oxygenfromthelungspassesintothese

（2）fordistributiontotissuecells,whilecarbondioxidefromthebloodpassesintothelungstobeexpelledbyexhalation.Onceabsorbedintobloodcells,oxygenbecomesattachedto（3）andisreleasedtotissuecellsasneeded.Thus,theprimaryfunctionofthelungsistobringairintoclosecontactwithblood,whichallows（4）tooccur.Thelungsaresurroundedbyamembranecalledthe（5