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

Chapter5

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,whatpreventsthepassingoffoodordrinkintothelarynxandrespiratorysystemafterithasbeenswallowedEvenwithasmallquantityofsolidorliquidmatterfindingitswayintotheairpassages,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,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.Thisthirdimportantcleaningdevice——likebreathing,underpartialvoluntarycontrol——isarapidmusclecontractionandbronchial-tubeconstrictionthatgeneratesawindforcefarstrongerthanatornado.Smallharmfulsubstancesthatmaketheirwayintothealveoliaredestroyedbythefourthlineofdefense,themacrophages.Thesearepatrollingcellsthat"swallowup"foreignparticlesordestroythemwithenzymes.

NewWordsandPhrases

Exercises

A.Discussthefollowingtopics:

1.Imagineyouwerelecturinginfrontofruralhealthworkersonthetopicofrespiratorysystem,drawapicturetoillustratethewholesystem.

2.Describetheirstructuresandfunctions.

3.Howcanepiglottispreventthepassingfoodanddrinkintotherespiratorysystem

4.Whatroledoesthediaphragmplayintheprocessofbreathing

5.WhatarethefourcomponentsofthecleaningsystemHowdotheyfunction

B.Fillintheblankswiththewordsgivenbelowandchangetheirformsifnecessary.

alveoluscapillary

diaphragmhemoglobin

thoraciccavity

gasexchange

parietalpleura

visceralpleura

mediastinumpleuralspace

Thelungsaretwocone-shaped,spongyorgansconsistingofalveoli,bloodvessels,elastictissueandnerves.Eachofthetwolungsconsistsofsmallerdivisionscalledlobes;theleftlunghastwolobes,whiletherightlungisdividedintothreelobes.Inthelungs,

（1）aresurroundedbyanetworkoftinybloodvesselscalledcapillaries;oxygenfromthelungspassesintothese

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