医学专业英语chapter5respiratorysystem.docx
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医学专业英语chapter5respiratorysystem.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.
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