第一章Tounderstandthehumanbodyitisnecessarytounderstandhowitspartsareputtogetherandhowtheyfunction.Thestudyofthebody'sstructureiscalledanatomy;thestudyofthebody'sfunctionisknownasphysiology.Otherstudiesofhumanbodyincludebiology,cytology,embryology,histology,endocrinology,hematology,immunology,psychologyetc.了解人體各部分的組成及其功能，對于認(rèn)識人體是必需的。研究人體結(jié)構(gòu)的科學(xué)叫解剖學(xué)；研究人體功能的科學(xué)叫生理學(xué)。其他研究人體的科學(xué)包括生物學(xué)、細(xì)胞學(xué)、胚胎學(xué)、組織學(xué)、內(nèi)分泌學(xué)、血液學(xué)、遺傳學(xué)、免疫學(xué)、心理學(xué)等等。Anatomistsfinditusefultodividethehumanbodyintotensystems,thatis,theskeletalsystem,themuscularsystem,thecirculatorysystem,therespiratorysystem,thedigestivesystem,theurinarysystem,theendocrinesystem,thenervoussystem,thereproductivesystemandtheskin.Theprincipalpartsofeachofthesesystemsaredescribedinthisarticle.解剖學(xué)家發(fā)現(xiàn)把整個(gè)人體分成骨骼、肌肉、循環(huán)、呼吸、消化、泌尿、內(nèi)分泌、神經(jīng)、生殖系統(tǒng)以及感覺器官的做法是很有幫助的。本文描繪并闡述了各系統(tǒng)的主要部分。Theskeletalsystemismadeofbones,jointsbetweenbones,andcartilage.Itsfunctionistoprovidesupportandprotectionforthesofttissuesandtheorgansofthebodyandtoprovidepointsofattachmentforthemusclesthatmovethebody.Thereare206bonesinthehumanskeleton.Theyhavevariousshapes-long,short,cube-shaped,flat,andirregular.Manyofthelongboneshaveaninteriorspacethatisfilledwithbonemarrow,wherebloodcellsaremade.骨骼系統(tǒng)由骨、關(guān)節(jié)以及軟骨組成。它對軟組織及人體器官起到支持和保護(hù)作用，并牽動骨胳肌，引起各種運(yùn)動。人體有206根骨頭。骨形態(tài)不一，有長的、短、立方的、扁的及不規(guī)則的。許多長骨里有一個(gè)內(nèi)層間隙，里面充填著骨髓，這即是血細(xì)胞的制造場所。Ajointiswherebonesarejoinedtogether.Theconnectioncanbesoclosethatnomovementispossible,asisthecaseintheskull.Otherkindsofjointspermitmovement:eitherbackandforthinoneplane-aswiththehingejointoftheelbow-ormovementaroundasingleaxis-aswiththepivotjointthatpermitstheheadtorotate.Awiderangeofmovementispossiblewhentheball-shapedendofonebonefitsintoasocketattheendofanotherbone,astheydointheshoulderandhipjoints.關(guān)節(jié)把骨與骨連接起來。顱骨不能運(yùn)動，是由于骨與骨之間的連接太緊密。但其它的關(guān)節(jié)可允許活動，如一個(gè)平面上的前后屈伸運(yùn)動，如肘關(guān)節(jié)；或是繞軸心旋轉(zhuǎn)運(yùn)動，如樞軸點(diǎn)允許頭部轉(zhuǎn)動。如果一根骨的球形末端插入另一根骨的臼槽里，大輻度的運(yùn)動（如肩關(guān)節(jié)、髖關(guān)節(jié)）即成為可能。Cartilageisamoreflexiblematerialthanbone.Itservesasaprotective,cushioninglayerwherebonescometogether.Italsoconnectstheribstothebreastboneandprovidesastructuralbaseforthenoseandtheexternalear.Aninfant'sskeletonismadeofcartilagethatisgraduallyreplacedbyboneastheinfantgrowsintoanadult.軟骨是一種比一般骨更具韌性的物質(zhì)。它是骨連結(jié)的保護(hù)、緩沖層。它把肋骨與胸骨連結(jié)起來，也是鼻腔與內(nèi)耳的結(jié)構(gòu)基礎(chǔ)。一個(gè)嬰兒的骨骼就是由軟骨組成，然后不斷生長、骨化，使嬰兒長大成人。Themuscularsystemallowsthebodytomove,anditscontractionsproduceheat,whichhelpsmaintainaconstantbodytemperature.Striatedmusclescanbeconsciouslycontrolled.Theendsofthesemusclesareattachedtodifferentbonesbyconnectivetissuebandssothatwhenthemusclecontracts,onebonemovesinrelationtotheother.Thismakesitpossibletomovethewholebody,aswhenwalking,ortomovejustonepartofthebody,aswhenbendingafinger.Contractionsoftheheartandsmoothmusclesarenotunderconsciouscontrol.Smoothmusclesarefoundinthewallsoforganssuchasthestomachandtheintestinesandservetomovethecontentsoftheseorgansthroughthebody.肌肉系統(tǒng)使軀體運(yùn)動，肌肉收縮產(chǎn)生的熱有助于維持一個(gè)恒定的體溫。人體能夠有意識地控制條紋肌。結(jié)締組織使肌肉末端附著于不同的骨面上，所以當(dāng)肌肉收縮時(shí)，兩骨彼此靠近而產(chǎn)生運(yùn)動。這也就使整個(gè)人體可以運(yùn)動起來，如走路，運(yùn)動軀體某個(gè)部位，如彎曲手指。心臟收縮和平滑肌收縮就不是被意識所控制的。器官壁內(nèi)層的平滑肌，如胃腸壁的平滑肌把胃腸中的物質(zhì)運(yùn)送到全身。Thecirculatorysystem.Allpartsofthebodymusthavenourishmentandoxygeninordertofunctionandgrow,andtheirwasteproductsmustberemovedbeforetheyaccumulateand物質(zhì)。Theliquidremainderofthefoodentersthelargeintestine,orcolon,whichisabout12feet(3.7meters)long.Itismorethantwiceaswideasthesmallintestine.Inthelargeintestinemostofthefluidisabsorbed,andtherelativelydryresiduesareexpelled.液狀的剩余食物進(jìn)入大腸，或結(jié)腸，它大約有12英尺（3.7米）長。大腸是小腸的兩倍多寬。大部分液體在大腸內(nèi)被吸收，相對干化的殘余物被排出體外。Theurinarysystemmaintainsnormallevelsofwaterandofcertainsmallmoleculessuchassodiumandpotassiuminthebody.Itdoesthisbypassingbloodthroughthekidneys,twoefficientfilteringorgansthatgetridofanyexcessofvariousmoleculesandconservethosemoleculesthatareinshortsupply.泌尿系統(tǒng)維持水分及體內(nèi)某些小分子物質(zhì)，如鈉、鉀的正常水平。身體是通過讓’腎過濾血液來做到這一點(diǎn)的。腎是兩個(gè)有效的過濾器官，它濾出各種多余的小分子物質(zhì)，保留那些供應(yīng)不足的小分子物質(zhì)。Thefluidthatleavesthekidneys,knownasurine,travelsthroughatubecalledtheuretertothebladder.Thebladderholdstheurineuntilitisvoidedfromthebodythroughanothertube,theurethra.從腎流出的液體，即尿，通過輸尿管人膀胱。膀胱起貯存尿液的作用，直到尿經(jīng)膀胱另一端的管道排出。Theendocrinesystem.Thetwosystemsthatcontrolbodyactivitiesaretheendocrinesystemandthenervoussystem.Theformerexertsitscontrolbymeansofchemicalmessengerscalledhormones.Hormonesareproducedbyavarietyofendocrineglands,whichreleasethehormonesdirectlyintothebloodstream.內(nèi)分泌系統(tǒng)。內(nèi)分泌和神經(jīng)是調(diào)控機(jī)體活動的兩個(gè)系統(tǒng)，前者依靠其化學(xué)信使——激素發(fā)揮作用。激素是由各種內(nèi)分泌腺體制造，并直接被釋放入血流Amajorglandisthepituitary,whichislocatedunderthebraininthemiddleofthehead.Itproducesatleasteighthormones,whichaffectgrowth,kidneyfunction,anddevelopmentofthesexorgans.Becausesomeofthepituitary'shormonesstimulateotherglandstoproducetheirownhormones,thepituitarycalledthemastergland.腦垂體是一個(gè)主要腺體，它位于頭中部腦下方。它至少分泌八種激素，這些激素對人體生長、肝功能及性器官發(fā)育有影響。因?yàn)槟X垂體分泌的一些激素促進(jìn)其他腺體分泌激素，所以腦垂體是主要腺體。Anothergland,thethyroid,islocatedbetweenthecollarbones.Itshormonecontrolstherateofthebody'smetabolism.Thesexorgans(ovariesendtestes)makethesexcellsandalsomakehormonesthatcontrolcertaincharacteristicsofmalesandfemales.Locatedontopofeachkidneyistheadrenalgland,whichproducescortisoneandadrenaline.Thepancreasproducesnotonlydigestiveenzymesbutalso3insulinandglucagon,whichcontrolthebody'suseofsugarandstarches.另一個(gè)腺體，甲狀腺，位于鎖骨之間。甲狀腺激素調(diào)控著機(jī)體新陳代謝的速度。性器官（卵巢、睪丸）分泌性細(xì)胞和性激素，這些激素控制著男性和女性的某些特征。每邊腎上方是腎上腺，它分泌可的松和腎上腺激素。胰腺不僅分泌消化酶，而且分泌胰島素和高血糖素，這兩種激素控制機(jī)體的糖分及淀粉的消耗。Thenervoussystem.Thebrain,thespinalcordandthenerve-alsocontrolsbodyactivities.Thelowerpartsofthebraincontrolbasicfunctionssuchasbreathingandheartrateaswellasbodytemperature,hunger,andthirst.Abovetheseregionsarethecentersforsight,sound,touch,smell,andtaste,andtheregionsthatdirectvoluntarymuscularactivitiesofthearmsandlegs.Performedherearethehigherfunctionsofintegratingandprocessinginformation.神經(jīng)系統(tǒng)——腦、脊髓及神經(jīng)，也調(diào)控機(jī)體活動。腦的偏下部位控制著諸如呼吸、心跳、體溫、饑渴的基本活動。而腦的偏上部位則是視覺、聽覺、觸覺、嗅覺及味覺中心，也是指揮臂、腿隨意肌肉運(yùn)動的區(qū)域。神經(jīng)系統(tǒng)更高級的功能是整合、處理信息。Thebrainreceivesandsendsinformationbymeansofnerves,manyofwhichliepartlyinthespinalcord.Thespinalcordisprotectedbythespinalcolumn.Nervesenterandleavethespinalcordateachlevelofthebody,travelingtoandfromthearms,legs,andtrunk.Thesenervesbringinformationfromthevarioussenseorgans.Theinformationisprocessedbythebrain,andthenmessagesarecarriedbacktomusclesandglandsthroughoutthebody.腦通過神經(jīng)收集并傳送信息，許多神經(jīng)部分地分布在脊髓里。脊髓由脊柱保護(hù)。在機(jī)體每一級，神經(jīng)傳人、傳出脊髓，往返于臂、腿、軀體。這些神經(jīng)輸送來自各種感覺器官的信息。信息經(jīng)腦處理后輸送回全身及腺體Thereproductivesystemisconstructeddifferentlyformalesandfemales.Themalereproductivesystemisresponsibleforproducing,transportingandmaintainingviablesperm(themalesexcell).Italsoproducesthemalesexhormone,testosterone,whichregulatesthedevelopmentofabeard,pubichair,adeepvoiceandotherbodilycharacteristicsoftheadultmale.男、女性的生殖系統(tǒng)不同。男性生殖系統(tǒng)產(chǎn)生、輸送、維持能存活的精子（男性性細(xì)胞）。它也分泌男性激素、睪酮，以此調(diào)節(jié)胡須、陰毛、深沉嗓音極其他成年男子身體發(fā)育的特征。Thefemaleproductivesystemisresponsibleforproducingandtransportingova(thefemalesexcells),eliminatingovafromthebodywhentheyarenotfertilizedbysperm,nourishingandprovidingaplaceforgrowthofanembryowhenanovumisfertilizedbysperm,andnourishinganewbornchild.Thefemalereproductivesystemalsoproducesthefemalesexhormones,estrogenandprogesterone,whichregulatethedevelopmentofbreastsandotherbodilycharacteristicsofthematurefemale.女性生殖系統(tǒng)產(chǎn)生、輸送卵子（女性性細(xì)胞），將未受精的卵子排出體外，而當(dāng)精、卵結(jié)合時(shí)，女性生殖系統(tǒng)培養(yǎng)、提供胚胎生長場所，并孕育新生兒。女性生殖系統(tǒng)也分泌女性性激素——雌激素和孕酮，以此調(diào)節(jié)乳房及其他成熟女性身體發(fā)育的特征。Theskinisacompletelayerthatprotectstheinnerstructuresofthebody,anditisthelargestofthebody'sorgans.Itkeepsoutforeignsubstancesandpreventsexcessivewaterevaporation.Thenervesintheskinprovidetactileinformation.Theskinalsohelpskeepthebody'stemperaturecloseto37°C,heatisconservedbyreducingbloodflowthroughtheskinorisexpendedbyincreasingbloodflowandbyevaporationofsweatfromtheskin.Hairandnailsareaccessorystructuresoftheskin.皮膚是保護(hù)肌體內(nèi)層結(jié)構(gòu)的完整層，也是機(jī)體的最大器官。皮膚防御外來侵襲，防止過多水分蒸發(fā)。皮膚上的神經(jīng)提供觸覺信息。皮膚也能將體溫維持到98.6華氏度（約37攝氏度）。通過皮膚的血流量降低時(shí)，熱量就被儲存起來，通過皮膚的血流增加及汗液蒸發(fā)時(shí)，熱量就散發(fā)。頭發(fā)及指甲是皮膚的附屬結(jié)構(gòu)。第二章HumanDiseasesThebriefsurveyofthehumanbodyinChapterOnehasgivenusaglimpseintotwodifferentstudiesthatareconsideredthefundamentalsofmedicalsciences,namelyanatomyandphysiology.However,thepictureisnotcompletewithoutconsideringpathology,thesciencethatdealswiththestructuralandfunctionalchangesproducedbythedisease.Infact,themodernapproachtothestudyofdisorderemphasizesthecloserelationshipofthepathologicalandphysiologicalaspectsandtheneedtounderstandthefundamentalsofeachintreatinganybodydiseases.第一章中，通過對人體的概論，即解剖學(xué)與生理學(xué)，我們對兩種被認(rèn)為是醫(yī)學(xué)基礎(chǔ)的不同學(xué)科有了一個(gè)大致的印象。然而如果我們不考慮病理學(xué)，這門涉及由疾病帶來的結(jié)構(gòu)和功能變化的學(xué)科，上述的人體概論就不是完整的。實(shí)際上，現(xiàn)代對疾病的研究方法強(qiáng)調(diào)了病理學(xué)與生理學(xué)方面的密切關(guān)系，強(qiáng)調(diào)了我們在治療任何人體疾病方面需要了解病理學(xué)與生理學(xué)基礎(chǔ)的重要性。Thenwhatisadisease?Itmaybedefinedasaconditionthatimpairstheproperfunctionofthebodyorofoneofitsparts.Everylivingthing,bothplantsandanimals,cansuccumbtodisease.People,forexample,areofteninfectedbytinybacteria,butbacteria,inturn,canbeinfectedbyevenmoreminuteviruses.那么什么是疾病呢？它可能被定義為正常的功能或是部分功能遭受損害時(shí)的一種狀態(tài)。每一種生物、植物和動物，都會受制于疾病。例如，人類常常被微小的細(xì)菌所感染，但是，反過來說，細(xì)菌又能夠被甚至更加微小的病毒所感染。Hundredsofdifferentdiseasesexist.Eachhasitsownparticularsetofsymptomsandsigns,cluesthatenableaphysiciantodiagnosetheproblem.Asymptomissomethingapatientcandetect,suchasfever,bleeding,orpain.Asignissomethingadoctorcandetect,suchasaswollenbloodvesseloranenlargedinternalbodyorgan.許多種疾病存在于世。每一種都有其特定的癥狀、征兆和線索，醫(yī)生能以此診斷疾病之所在。癥狀是病人自己就能覺察到的，比如，高燒、流血，或是疼痛。而征兆則是醫(yī)生能夠觀察到的，比如，血管擴(kuò)張或是體內(nèi)器官腫大。Diseasescanbeclassifieddifferently.Forinstance,anepidemicdiseaseisonethatstrikesmanypersonsinacommunity.Whenitstrikesthesameregionyearafteryearitisanendemicdisease.Anacutediseasehasaquickonsetandrunsashortcourse.Anacuteheartattack,forexample,oftenhitswithoutwarningandcanbequicklyfatal.Achronicdiseasehasaslowonsetandrunsasometimesyears-longcourse.Thegradualonsetandlongcourseofrheumaticfevermakesitachronicailment.Betweentheacuteandchronic,anothertypeiscalledsubacute.疾病可以劃分為不同的種類，例如，流行病是一種在某一社區(qū)內(nèi)侵襲許多人的疾病。當(dāng)它年復(fù)一年地襲擊同一社區(qū)，就成了一種地方病。急性病發(fā)作快，但病程短，舉個(gè)例子來說，急性心臟病發(fā)作常常沒有前兆，而且會很快致命。慢性病發(fā)作則慢，但病程有時(shí)會長達(dá)幾年之久。風(fēng)濕熱正是由于發(fā)病慢、病程長而成為一種慢性失調(diào)病（慢性?。６橛诩毙耘c慢性之間的另一種類型，就被稱為亞急性。Diseasescanalsobeclassifiedbytheircausativeagents.Forinstance,aninfectious,orcommunicable,diseaseistheonethatcanbepassedbetweenpersonssuchasbymeansofairbornedropletsfromacoughorsneeze.Tinyorganismssuchasbacteriaandfungicanproduceinfectiousdiseases.Socanviruses.Socantinyworms.Whateverthecausativeagentmightbe,itsurvivesinthepersonitinfectsandispassedontoanother.Sometimes,adisease-producingorganismgetsintoapersonwhoshowsnosymptomsofthedisease.Theasymptomaticcarriercanthenpassthediseaseontosomeoneelsewithoutevenknowinghehasit.疾病也可以依其病原體來劃分，例如，傳染病也叫作可傳播的疾病，就是一種通過咳嗽和打噴嚏造成的空氣小粒來傳播的疾病。極小的有機(jī)體，如，細(xì)菌和真菌可導(dǎo)致傳染病。病毒和小蟲子也不例外。不論病原體會是什么樣，只要它存活于人體內(nèi)就能夠傳染給別人。有時(shí)，一個(gè)致病的有機(jī)體侵人人體后，該人卻沒有顯示帶病的癥狀。于是無癥狀的病原攜帶者甚至在自己也不知情的情況下就把疾病傳染給了他人。Noninfectiousdiseasesarecausedbymalfunctionsofthebody.Theseincludeorganortissuedegeneration,erraticcellgrowth,andfaultybloodformationandflow.Alsoincludedaredisturbancesofthestomachandintestine,theendocrinesystem,andtheurinaryandreproductivesystems.Somediseasescanbecausedbydietdeficiencies,lapsesinthebody'sdefensesystem,orapoorlyoperatingnervoussystem.非傳染性疾病是由身體功能失調(diào)引起的。這包括血管或組織退化、異常細(xì)胞生成，以及異常的血液生成和血液循環(huán)。當(dāng)然其中也包括胃、腸、內(nèi)分泌系統(tǒng)和泌尿生殖系統(tǒng)的紊亂。一些疾病也可能是由飲食不足、身體抵抗力下降、或是神經(jīng)系統(tǒng)工作不造成的。Disabilityandillnessescanalsobeprovokedbypsychologicalandsocialfactors.Theseailmentsincludedrugaddiction,obesity,malnutrition,andpollution-causedhealthproblems.心理因素和社會因素也會引發(fā)殘廢和疾病，這些病包括吸毒成性、肥胖、營養(yǎng)不良和由污染造成的健康問題。Furthermore,athousandormoreinheritablebirthdefectsresultfromalternationsingenepatterns.Sincetinygenesareresponsibleforproducingthemanychemicalsneededbythebody,missingorimproperlyoperatinggenescanseriouslyimpairhealth.Geneticdisordersthataffectbodychemistryarecalledinbornerrorsofmetabolism.Someformsofmentalretardationarehereditary.而且，有上千種乃至為數(shù)更多的遺傳性出生缺陷是由于基因變化而造成的。由于小小的基因負(fù)責(zé)著生產(chǎn)許多身體所需的化學(xué)物質(zhì)，它的遺失或是工作狀態(tài)不良都會嚴(yán)重?fù)p害健康。因基因失調(diào)而被影響了的身體化學(xué)反應(yīng)被稱之為先天性代謝失調(diào)。一些眢力發(fā)育遲緩就是因遺傳而造成的。HowGermsInvadetheBody病菌是怎樣侵襲身體Humansliveinaworldwheremanyotherlivingthingscompeteforfoodandplacestobreed.Thepathogenicorganisms,orpathogens,oftenbroadlycalledgerms,thatcausemanydiseasesareabletoinvadethehumanbodyanduseitscellsandfluidsfortheirownneeds.Ordinarily,thebody'sdefensesystemcanwardofftheseinvaders.人類生活在有一個(gè)有許多其它生物競爭食物和求得繁衍的世界里。很多致病的有機(jī)體或病原體，通常被我們廣義地稱為病菌的東西能侵入人體并利用其細(xì)胞和組織液來供它們自身的需求。一般來講，身體防御系統(tǒng)能夠阻止這些入侵者。Pathogenicorganismscanenterthebodyinvariousways.Some-suchasthesethatcausethecommoncold,pneumonia,andtuberculosis-arebreathedin.Others-suchasthosethatcausevenerealdiseases-enterthroughsexualcontactofhumanbodies.Stillothers-suchasthosethatcausehepatitis,colitis,cholera,andtyphoidfever-getinthebodythroughcontaminatedfood,waterorutensils.病原有機(jī)體能通過多種方式進(jìn)入身體。它們的一些是被呼吸進(jìn)體內(nèi)的，比如那些引起普通感冒、肺炎和肺結(jié)核的病菌；其它的是通過人體性接觸進(jìn)入的，比如那些引起花柳病的病原體；還有另外的一些是通過污染了的食物、水或器皿進(jìn)入體內(nèi)的，比如那些引起肝炎、霍亂和傷寒熱的病原體。Insectscanspreaddiseasebyactingasvectors,orcarriers.Fliescancarrygermsfromhumanwasteorothertaintedmaterialstofoodandbeverages.Germsmayalsoenterthebodythroughthebiteofamosquito,louse,orotherinsectvector.昆蟲作為媒介動物或是病原攜帶者會傳播疾病。蒼蠅能將病菌從人類的廢物或其它腐爛的材料中帶到食物和飲料中去。通過蚊子、虱子或其它媒介動物的叮咬，病菌也可能進(jìn)入體內(nèi)。HowtheBodyFightsDisease身體是怎樣抵抗疾病的Asafirstlineofdefense,ahealthybodyhasanumberofphysicalbarriersagainstinfection.Theskinandmucousmembranescoveringthebodyorliningitsopeningsofferconsiderableresistancetoinvasionbybacteriaandotherinfectiousorganisms.Ifthesephysicalbarriersareinjuredorburned,infectionresistancedrops.Inminorcases,onlyboilsorpimplesmaydevelop.Inmajorcases,however,largeareasofthebodymightbecomeinfected.作為第一條防線，一個(gè)健康的身體有許多屏障來抵御感染的發(fā)生。覆蓋在體表或者器官開口處的皮膚和粘膜能在很大程度上抵抗細(xì)菌或其它感染體的入侵。如果這些屏障遭到了損壞或燒傷，身體對感染的抵抗力就會下降。在一些病情較輕的病例中，疥子和小膿胞可能會發(fā)生。在病情較重的病例中，身體的大面積區(qū)域則可能會被感染。Breathingpassagesareespeciallyvulnerabletoinfection.Fortunately,theyarelinedwithmucus-secretingcellsthattraptinyorganismsanddustparticles.Also,minutehairscalledcilialinethebreathingpassages,wavelikeafieldofwheat,andgentlysweepmatteroutoftherespiratorytract.Inaddition,foreignmatterinthebreathingpassagescanoftenbeejectedbynoseblowing,coughing,sneezing,andthroatclearing.Unfortunately,repeatedinfection,smokingandothercausescandamagetherespiratorypassagewaysandmakethemmoresusceptibletoinfection.呼吸通道尤其容易受到感染，幸運(yùn)的是，呼吸道內(nèi)覆蓋滿了能分泌粘液的細(xì)胞，它們能捕捉微小的有機(jī)體和塵粒。另外，被叫做纖毛的細(xì)小的毛發(fā)也覆蓋了呼吸道，它們象微風(fēng)下麥田里的小麥一樣舞動著，輕輕地將異物掃出呼吸道。除此之外，呼吸道內(nèi)的異物還常常因?yàn)檫┍翘?、咳嗽、打噴嚏和清喉嚨而被彈出。不幸的是反?fù)感染、抽煙或其它別的原因會損壞呼吸道，并且使它們?nèi)菀资艿礁腥綧anypotentialinvaderscannotstandbodytemperature(98.6°For37°C).Eventhosethatthriveatthattemperaturemaybedestroyedwhenthebodyassumeshigher,fevertemperatures.很多潛在的人侵者不能在華氏98.6度或攝氏37度下生存。如果體溫再升高一點(diǎn)，達(dá)到高燒溫度，甚至一些在先前溫度下能蓬勃繁殖的病菌也可能會因此而遭到毀滅。Waxintheouterearcanalsandtearsfromeyeductscanslowthegrowthofsomebacteria.Andstomachacidcandestroycertainswallowedgerms.外耳道里的蠟質(zhì)和淚管里的眼淚能減緩一些細(xì)菌的生長速度，而胃酸也能毀掉某種吞食進(jìn)去的病菌。Thebody'ssecondlineofdefenseisinthebloodandlymph.Certainwhitebloodcellsflocktoinfectedareasandtrytolocalizetheinfectionbyformingpus-filledabscesses.Unlesstheabscessbreaksandallowsthepustodrain,theinfectionislikelytospread.Whenthishappens,theinfectionisfirstblockedbylocallymphglands.Forexample,aninfectioninthehandtravelsupthearm,producingredstreaksandswollen,tenderlymphglandsinthearmpit.Unlesstheinfectionisbroughtundercontrol,itwillresultinbloodpoisoning.身體的第二條防線是在血液和淋巴里。某些白細(xì)胞群聚集在被感染區(qū)，并通過形成膿塊使感染局部化。如果膿塊不破裂，里面的膿不排除掉，感染很可能會擴(kuò)大。當(dāng)這發(fā)生時(shí)，感染首先被該區(qū)域的淋巴腺擋住。例如，手上的感染在向上傳到手臂時(shí)，手臂上會出現(xiàn)紅線條，腋窩處會腫脹，有觸痛。如果不及時(shí)控制住感染的上傳，將會導(dǎo)致血液中毒。Phagocytesarelocatedatvarioussitestominimizeinfection.Onetypeinthespleenandliverkeepsthebloodclean.Othersinsuchhigh-riskareasasthewallsofthebronchiandtheintestinesremovecertainbacteriaandshatteredcells.吞噬細(xì)胞處于身體多種不同的部位而使得感染的機(jī)會變小。位于肝脾內(nèi)的一類能使身體的血液保持干凈。其它的位于像支氣管壁和腸壁這樣高危險(xiǎn)區(qū)的類型能清除某類細(xì)茵和已解體的細(xì)胞。HowWeBecomeImmunetoDisease我們是怎樣變得對疾病有免疫力的身體處理感染有其特殊的方法。Thebodyhasaspecialwayofhandlinginfection.Ithasasystemthatfendsoffthefirsttracesofaninfectioussubstanceandthen,througha"memory,"givesthebodyalong-lastingimmunityagainstfutureattacksbythesamekindofinvader.它有一個(gè)系統(tǒng)，能夠一開始就阻止感染性物質(zhì)的侵襲，然后通過“記憶”，它能給身體—個(gè)長期的免疫力來抵抗將來由同種入侵者引起的侵襲。Manysubstancescouldharmthebodyiftheyeverenteredit.Thesesubstances,orantigens,rangefrombacteriaandpollentoatransplantedorgan(viewedbythebodyasaninvader).Tofightthemthebodymakesspecialchemicalsknownasantibodies.許多物質(zhì)對身體有害，如果它們一旦進(jìn)入身體的話。這些物質(zhì)，或稱為抗原，包括從細(xì)菌，花粉到被移植的器官都被身體視為人侵者。為了抵抗它們身體制造出了特殊的化學(xué)物質(zhì)，這就是抗體。Antibodiesareaclassofproteinscalledimmunoglobulins.Eachantibodyismadeofaheavychainofchemicalsubunits,oraminoacids,andalightchainofthem.Thelightchainhasspecialsiteswheretheaminoacidscanlinkwiththeircomplementsontheantigenmolecule.Whenanantibodyhooksupwithanantigen,itoftenputstheantigenoutofactionbyinactivatingorcoveringakeyportionoftheharmfulsubstance.Insomecases,throughtheprocessofopsonization,antibodies"butter"thesurfaceofsomeantigensandmakethem"tastier"tophagocytes,whichengulftheantigens.Sometimesanantibodyhookstoabacterialantigenbutneedsanintermediate,orcomplement,toactuallydestroythebacterium.Astheantibody-antigencomplexcirculatesintheblood,thecomplex"fixes"complementtoit.Inturn,thecomplementcausespowerfulenzymestoeatthroughthebacterialcellwallandmaketheorganismburst.抗體是一類被稱為免疫球蛋白的蛋白質(zhì)。每一個(gè)抗體由一條化學(xué)亞單位（即氨基酸）的重鏈和一條輕鏈所構(gòu)成。這條輕鏈上有特別的部位，在那里，氨基酸能使其補(bǔ)體和抗原分子相連。當(dāng)一個(gè)抗體與一個(gè)抗原粘和上以后，氨基酸常通過使抗原失去活性或覆蓋，它的關(guān)鍵有害部分來使抗原失去其作用。在某些情況下，通過調(diào)理素作用的過程，抗體在抗原表面涂抹上一些“奶油”，讓吞噬細(xì)胞更喜歡吞噬它們。在另一些情況下，抗體和一個(gè)細(xì)菌抗原粘和上以后，卻需要一個(gè)中間體，或補(bǔ)體來實(shí)施對該細(xì)菌的消滅。于是，當(dāng)抗體和抗原的結(jié)合體隨血液循環(huán)時(shí)，該結(jié)合體會有一個(gè)補(bǔ)體附體。結(jié)果是補(bǔ)體產(chǎn)生一種強(qiáng)烈的酶，咬穿了細(xì)菌的細(xì)胞壁，細(xì)菌有機(jī)體就爆開了。Thereareseveralkindsofimmunoglobulins-IgM,thelargest;IgG,themostplentifulandversatile;andIgA,thenextmostplentifulandspeciallyadaptedtoworkinareaswherebodysecretionscoulddamageotherantibodies.Otherimmunoglobulinsaretiedinwithallergicreactions,IgMismadeatthefirstsignsofanantigen,anditislatersupplantedbythemoreeffectiveIgG.抗體有若干種免疫球蛋白：體積最大的是igM，數(shù)量最多、用途最多的是IgG，而IgA的數(shù)量次多，但它特別適合在其它抗體易被身體內(nèi)分泌物殺死的部位工作，還有其它的免疫球蛋白專門在過敏物質(zhì)出現(xiàn)時(shí)啟動。一有抗原出現(xiàn)，igM首先被產(chǎn)生，稍后被更有效的IgG所取代。Wheninfectionfirststrikes,theimmunitysystemdoesnotseemtobeworking.Duringthefirstdayorso,antibodiesagainsttheinfectioncannotbefoundintheblood.Butthisisonlybecausethebasiccellsinvolvedinantibodyproductionhavebeentriggeredbythepresenceofantigentomultiplythemselves.Theantibodylevelstartstoriseonabouttheseconddayofinfectionandthenzoomsupward.Bythefifthdaytheantibodylevelhasrisenathousandfold.當(dāng)傳染病首次進(jìn)攻，免疫系統(tǒng)似乎沒有運(yùn)轉(zhuǎn)起來。在第一天左右，血液中沒有發(fā)現(xiàn)對付傳染病的抗體。但是，這只是因?yàn)樯婕翱贵w制造的基本細(xì)胞已被當(dāng)前的抗原存在所觸發(fā)而正準(zhǔn)備開始繁殖。大約在感染的第二天，抗體水平開始升高，接著直線上升，大約在第五天抗體水平已升高了千倍。Thefirstantibodies,thelargeIgMtype,arenotthebestqualifiedtofightawiderangeofantigens,buttheyareparticularlyeffectiveagainstbacteria.ThemoreversatileIgGiscirculatinginthebloodonaboutthefourthdayofinfection.ItsproductionisstimulatedbytherisinglevelofIgMintheblood.Atthistime,IgMproductiondropsoffandtheimmunitysystemsconcentratesonmakingIgG.TheIgGtypeofantibodystickswelltoantig