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Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4087_Библиотеки_им_академика_М_И_Перельмана

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Chapter2—
WhatareVaricoseVeins?
Thischapterhelpsyoutounderstandwhatvaricoseveinsareandhowtheydevelop.Thisrequiressomeelementaryknowledgeaboutthecirculationofthebloodand
thestructureofbloodvessels.SowewillbejoggingyourmemorybacktoBiologylessonsatschool!
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Thereare,ofcourse,veinsalloverourbodies.Therearetwobasictypes:somearedeepwithinthetissuesandothers,thesuperficialveins,nearthesurfaceofour
skin.Likeanyotherorganofthebodytheytoocangowrong,anditseemsthattheveinsinourlegsaremorevulnerablethanthosealmostanywhereelseinourblood
circulatorysystem.
What,then,makesanordinarysurfacelegveinintoavaricosevein?Avaricoseveincanbedescribedasaveinthathaslostitselasticity.Inessence,ithasbecome
weakandflabby,anditexpands,ordilates,easily.Thefirstsignthatoneofyourveinsisvaricoseisthatwhenyoustanduptheveinbecomesobviouslyswollenwith
blood.Butwhy
Atypicalexampleofvaricoseveinsshowinghow
theyswellwhenyoustandup.
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shouldveinsbecomedilatedwhenyoustandup?Whyisitthatonlyveinsbecomevaricose?Toanswerthesequestionsandtohelpyouunderstandtheunderlying
causesforyourvaricoseveinsweshouldtakealookatthewaybloodcirculatesaroundourbodiesandtheparttheveinsplayintheprocess.
TheCirculationoftheBlood
Mostofyouwillprobablyneedyourmemoriesjoggedbacktoyourschooldayswhenyoudidalittleanatomyinyourbiologyclasses,orwhenyouweretaughtfirst
aid.
Theheart(seepreviouspage)isreallyjustapumpmadeofmuscle,roughlythesizeofyourfist.Actuallyit'sadoublepump,divideddownthemiddleintorightand
leftcompartments.Thesecompartmentsarefurtherdividedintotopandbottomchambers.Thetopchambers,knownasatria,arethinwalled;thebottomchambers,
knownasventricles,havethick,muscularwalls.
Theleftventriclehasthejobofpumpingoutbloodallaroundthebodyandsohasthicker,morepowerfulwallsthantherightventricle,whichonlyhastopumpblood
tothelungsnearby.Therightsideoftheheartreceivesbloodfromtheveins,whosejobitistoreturnbloodfromeverypartofthebody(apartfromthelungs)tothe
heart;thisbloodisalsopumpedintothelungs.Theleftsideoftheheartreceivesonlythebloodreturningfromthelungsandpumpsthisoutintoallpartsofthebody,
thuscompletingthecycle.
TheFunctionsoftheBlood
Thebloodthatenterstherightsideoftheheartfromtheveinshasalreadygivenupagooddealofitsoxygentothebody'stissuesandinturnithasreceivedwaste
productsproducedbythebody,particularlycarbondioxide.(Ineffect,thebloodactsasashuttle,takingoxygentothetissuesandtakingawaywasteproductssuch
ascarbondioxide,whichisthenexpelledviathelungs.)Thisbloodisdarkblueincolourbecauseitislowinoxygen(whichturnsbloodcellsred)andisknownas
venous,ordeoxygenated,blood.
Venousbloodthatistosaybloodfromtheveinsenterstherightatrium,passesthroughaonewayvalveandenterstherightventricle.Fromherethebloodis
pumpedthroughthepulmonary(orlung)valve,whichallowsonlyaonewayflowintothepulmonaryarteriesand
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Thecirculation
Thecirculationofbloodfromthebodythroughthehearttothelungs.From
thelungstheoxygenatedbloodreturnstotheheartandcirculatestotherest
ofthebody.
throughthemintothelungs.Onceinthelungs,thevenousbloodentersanetworkofminutehairlikebloodvesselsknownascapillarieswhichspreadthebloodthinly
overthesurfaceofthespongelikelungtissue.Thebloodgivesupitscarbondioxide,whichisbreathedoutintheexpiredair.Atthesametimeoxygenfromthe
breathedinairistakenintotheblood.Theoxygenatedbloodthenreturnstotheleftsideoftheheartintotheatrium,andfromhereitpassesintotheleftventri
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cle.Thisfreshlyoxygenatedbloodisthenpumpedoutthroughthemainartery,theaorta,crossingtheaorticvalve,whichpreventsthebloodfloodingbackintothe
heart,fordistributionthroughoutthebody.
Theheartisoneofthosestructuresthatamazesbothdoctorsandengineers.Itcarriesoutasteadyrhythmicactivity,contractingabout70timesaminute,yearin,year
out,oftenfor70yearsormorewithoutanytrouble.Itpumpsabout4000gallons(or18200litres)ofblooddailythroughsomethinglike60000miles(or96500
kilometres)ofbloodvesselsinanetworkthroughoutthebody.Ithastheabilityaccuratelytoadjustitsrateandtoforcetoyourbody'sneeds,increasingduring
exercise,slowingwhileyousleep.Ifaninventorcouldcreateamachineanywherenearapproachingtheheart'ssimplicityandefficiencytheworldwouldbeathisfeet!
TheArteries,CapillariesandVeins
Themuscularpumpthatistheheartprovidesthemotivepowertodrivethebloodoutintoallthemainarteriesandaroundthebody.Thisdrivingforceineachofusis
measuredasourbloodpressure,whichinahealthy,youngadultispowerfulenoughtoraiseacolumnofmercury(aheavyliquidmetal)about120millimetreshigh.
Thisiswhatthedoctormeasuresinmillimetresofmercury(mmHg)whenaninflatablecuffiswrappedaroundyourarmandyourbloodpressureistaken.
Thefunctionofthearteriesistodistributeoxygenatedbloodthroughoutourbodies.Theirtough,partlyelastic,partlymuscular,smoothwalledtubesprogressively
divide,ratherlikethebranchesorrootsofatree,intosmallerandsmallerchannels,thesmallestbeingcapillaries.Theseminutetubes,thethicknessofasinglecell,are
oftenonlywideenoughtoallowthebloodcells(orcorpuscles)tosqueezealongthemoneatatime.Youcangetsomeideaofjusthowsmalltheyarewhenyou
realizethat7000bloodcorpuscleswouldsidebysideonlymeasure1millimetreindiameter.
Itisatthecapillarylevelthatthebloodcarriesoutitsvitaljobofnourishingthetissuesofourbodies.Oxygenandessentialnutrients,suchassugar,arepassedthrough
thecapillarywallstothetissues,whilecarbondioxideandchemicalssuchasureathewasteproductsofcellactivitypassbackintothebloodandareeventually
passedout
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Arteriesaretough,thickwalledtubes.Veinsarethinandflimsyin
comparison,andtheirlackofmusclemakesthemsusceptibletoswelling.
ofourbodies,thecarbondioxidepassesoutofourlungsasagaswhiletheureaisdilutedwithwaterinourbodiesandispassedoutasurine.
Thecapillarynetworkthenreforms,firstintotinytubesknownasvenules,whichthenjoinupwitheachothertoformthebiggerveins.Theveinshaveonlyone
purposeandthatistocarrybloodbacktotheheart.Incontrastwiththethickwalled,musculararterieswhichhavetotakethebloodaroundthebody,yourveinsare
thintubes,mostlymadeupofsupportingconnectivetissue,andtheyhaveonlysmallamountsofmuscleintheirwalls.
KeepingBloodMovingintheVeins
Asthebloodtricklesthroughthenetworkofcapillaries,thepressurefallstoonlyafewmmHg,sowhatistheforcethatgetsthebloodbackalongtheveinstothe
heart?Whenweliedowntheforceofgravity
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Arteriescarrybloodtothetinycapillarieswhereitgivesupitsoxygenandnutrients.
Thebloodiscarriedbacktotheheartbytheveins.
helpstheflowalongbutwhataboutwhenwestandupandbloodhastobeforceduphillfromtheveinsinthefeetbacktotheheart?
Therearethreethingsthathelp(seediagramonpreviouspage).Thefirstisthepressurefrombehind,theslightpressurepushingbloodonwardsfromthecapillaries
intothevenules.Althoughthisissufficientwhenweliedown,itistotallyinadequatewhenwearestandingorwalking.Secondisthesuctioneffectofthelungs;when
wetakeadeepbreathanegativepressure,ratherlikeavacuum,iscreatedinthechestthathelpstodrawbloodupwardstotheheart.Thethird,however,isthemost
importantofall.Infact,itisabrilliantmechanism:thepumpingactionofthelegmuscles.Thesemusclesareenclosedinadensesheathoffibroustissue(calledthe
deepfascia).Whenyouwalkabout,themusclescontractandtheveinscontainedinthefibroussheatharesqueezed.Atintervalsalongtheinsidesoftheveinsare
beautifullyconstructedvalves,consistingoftwoflapsthatmeeteachotherexactly.Thoughverysimpletheyarequitesufficientneverthelesstomakesurethatthe
bloodcanbesqueezedinonedirectiononly—backtotheheart.
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Thethreeforceshelpingtokeepbloodmovinginthelegveins.
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1.Thetwovalvecuspscometogether,preventingbackflowofblood.
2.Thesevalvesonlyopentoallowbloodtotraveltowardstheheart.
Nowwhileallthisseemslikeacleversolutiontopumpthebloodinourveinsbacktoourheartsthereremainsoneproblemandthatishowtogetbloodbackfrom
theskinandthefattytissuesofthelegthatlieoutsidethisfibroussheath.
Again,aningeniouspieceofdesignisusedthatwouldmakeanyengineerproud.Theveinsthatdrainthesesuperficialtissuesarelinkedupwiththedeepveinsthrough
anumberofperforationsinthefibroussheath.Eachlinkingorcommunicationveinisguardedbyaonewayvalve.Aswewalk,themusclepumpsqueezesthedeep
veinsinourlegs;bloodispushedupwardstowardstheheart;andthenegativepressurewithinthedeepveinssucksinbloodthroughthecommunicatingveinsfromthe
skinandthefat.AsweshallseeinChapter3,itiswhenthisbrilliantbutdelicatepieceofapparatusisunabletodoitsjobforsomereasonthatvaricoseveinsdevelop.
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Page14
WhichVeinsBecomeVaricose?
Thesuperficialorsurfaceveinsofourlegs,andthesearetheonesthatdevelopintovaricoseveins,arecalledlongandshortsaphenousveins.Theword`saphenous'
comesfromtheArabicwordmeaning`easilyvisible',andcertainlythelowermostpartoftheveinsoftheleg,aroundtheankleandonthefrontofthefoot,arevisible
inperfectlynormalpeople.Thelongsaphenousveincanbeseenjustinfrontofyouranklejointonitsinnerside.Theveinrunsupwardsalongtheinnersideofyour
leg,behindthekneecapintothethigh.Itthenpassesthroughthefibroussheathofyourlegatthegrointoenterthefemoral(thigh)vein.Thisisthemostimportantof
themanylinkingveinsbetweenthesurfaceanddeepveinsoftheleganditisherethatthesurgeonoftenhastooperateinthosepatientswithseverevaricoseveins
(seepage50).
Theshortsaphenousveinbeginsbehindtheoutersideofyourankleandrunsupbehindthelegtothebackofyourknee.Hereittoopenetratesthroughthefibrous
sheathofyourlegtoenteralargedeepveincalledthepopliteal,whichchangesitsnameintothefemoralalittlehigherinthethigh.Aswellasthesetwomajorlinking
veins,atthegroinandbehindtheknee,therearemanyotherconnectionsbetweenthesurfaceanddeepveins,andeachisguardedbyavalvethatallowsbloodto
flowonlyfromthesurfacetothedeepveins—wheneverythingisworkingnormally,thatis.
TheFineStructureofVeins
Ifyoulookatalegveinunderamicroscope(seephotographonpage16),youwillseethatitismadeupofthreelayers.Theinnermostlayerisasmooth,shining
membranemadeupofflattenedcellswithirregularoutlinesthatfittogetherratherlikethepiecesofajigsawpuzzle.Themiddlelayercontainstheelastictissuethat
allowstheveintostretch,andtherearealsosomemusclefibresthatallowtheveintocontract.Theoutermostlayerisreallyjustacoatofaconnectivetissue.
Thesurfaceveinshavequiteaconsiderableamountofsmoothmuscleintheirwalls,farmorethaninthedeepveins.Thismeansthatthesurfaceveinscancontractin
responsetoinjuryorcoldandmayexpandinresponsetoheatandtochemicals,suchasthefemalesexhormones.Thedeepveins,ontheotherhand,aremuchmore
likepassivetubes
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