chpater12 Blood and Lymphatic and Immune System.docx

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chpater12BloodandLymphaticandImmuneSystem

Chapter12

BloodandtheLymphatic

AndImmuneSystem

PartI:

Blood

AnatomyandPhysiologyofBlood

Theaverageadulthasabout5litersofblood.Itcirculatesthroughoutthebodywithinthebloodvesselsofthecardiovascularsystem.Bloodisamixtureofcellsfloatinginwateryplasma.Asagroupthesecellsarereferredtoasformedelements,buttherearethreedifferentkinds:

erythrocytesorredbloodcells,leukocytesorwhitebloodcells,andplatelets.Bloodcellsareproducedintheredbonemarrowbyaprocesscalledhematopoiesis.Plasmaanderythrocytesareresponsiblefortransportingsubstances,leukocytesprotectthebodyfrominvadingmicroorganismandplateletsplayaroleincontrollingbleeding.

Plasma

Liquidplasmacomposesabout55percentofwholebloodintheaverageadultandis90to92percentwater.Theremaining8-10percentportionofplasmaisdissolvedsubstances,especiallyplasmaproteinssuchasalbumin,globulins,andfibrinogen.Albuminhelpstransportfattysubstancesthatcannotdissolveinthewateryplasma.Therearethreemaintypesofglobulins.Oneofthese,gammaglobulins,actsasantibodies.Fibrinogenisablood-clottingprotein.Inadditiontotheplasmaproteins,smalleramountsofotherimportantsubstancesarealsodissolvedintheplasmafortransport:

calcium,potassium,sodium,glucose,aminoacids,fats,andwasteproductssuchasureaandcreatinine.

Erythrocytes

Erythrocytesarealsocalledredbloodcells（RBCs）.Theyarebiconcavedisksandareenucleated,whichmeanstheynolongercontainanucleus.Redbloodcellsappearredincolorbecausetheycontainhemoglobin,whichisaniron-containingpigment.Hemoglobinisthepartoftheredbloodcellthatpicksupoxygenfromthelungsanddeliversittothetissuesofthebody.

Thereareabout5millionerythrocytespercubicmillimeterofblood.Thetotalnumberinanaverage-sizedadultis35trillion,withmaleshavingmoreredbloodcellsthanfemales.Erythrocyteshaveanaveragelifespanof120daysandthenthespleenremovestheworn-outanddamagedonesfromcirculation.Muchoftheredbloodcell,suchastheiron,canbereusedbutoneportion,bilirubin,isdisposedofbytheliver.

Leukocytes

Leukocytes,alsoreferredtoaswhitebloodcells（WBCs）,provideprotectionagainsttheinvasionofpathogenssuchasbacteria,viruses,andotherforeignmaterial.Ingeneral,WBCshaveasphericalshapewithalargenucleusandthereareabout8,000percubicmillimeterofblood.TherearefivedifferenttypesofWBCs,eachwithitsownstrategyforprotectingthebody.Thefivecanbesubdividedintotwocategories:

granulocytes（withgranulesinthecytoplasm）andagranulocytes（withoutgranulesinthecytoplasm）.ThenameandfunctionofeachtypeispresentedinTable12.1.

Table12.1LeukocyteClassification

Leukocyte

Function

Granulocytes

Basophils

Releasehistamineandheparintodamagedtissues

Eosinophils

Destroyparasitesandincreaseduringallergicreactions

Neutrophils

Importantforphagocytosis:

mostnumerousoftheleukocytes

Agranulocytes

Monocytes

Importantforphagocytosis

Lymphocytes

Provideprotectionthroughanimmunityacivity

Platelets

Plateletisthemoderntermforthrombocyte.Plateletsarethesmallestofalltheformedbloodelements.Theyarealsonotwholecells,butratherareformedwhenthecytoplasmofalargeprecursorcellshattersintosmallplate-likefragments.Therearebetween200,000and300,000percubicmillimeterinthebody.

Plateletsplayacriticalpartintheblood-clottingprocessorhemostasis.Theyagglutinateorclumptogetherintosmallclusterswhenabloodvesseliscutordamaged.Plateletsreleaseasubstancecalledthromboplastin,which,inthepresenceofcalcium,reactswithprothrombintoformthrombin.Thenthrombin,inturn,workstoconvertfibrinogentofibrin,whicheventuallybecomesthemesh-likebloodclot.SeeFigure12.1.

Figure12.1CompositionofBlood

Table12.2CompositionofBlood

Plasma55%

Constituent

Majorfunctions

Water

Solventforcarryingothersubstances

Salts

Sodium,Potassium,Calcium,Magnesium,Chloride,Bicarbonate

Osmoticbalance,pHbuffering,andregulationofmembranepermeability

Plasmaproteins

Albumin

Fibrinogen

Globulins

Osmoticbalance,pHbuffering

Clottingofblood

Defense（antibodies）andlipidtransport

Substancestransportedbyblood

Nutrients（e.g.,glucose,fattyacids,vitamins,aminoacids）

Wasteproductsofmetabolism（urea,uricacid）

Respiratorygases（O2andCO2）

Hormones

FormedElements（CellularComponents）45%

Celltype

Number（permm3ofblood）

Functions

Erythrocytes

（redbloodcells）

4-6million

Transportoxygenandhelptransportcarbondioxide

Leukocytes

（whitebloodcells）

4000-11,000

Defenseandimmunity

Platelets

250,000-500,000

Bloodclotting

BloodTyping

Eachperson’sbloodisdifferentfromothers’duetothepresenceofmarkerproteinsonthesurfaceofhisorhererythrocytes.Beforeapersonreceivesabloodtransfusionitisimportanttodoabloodtyping.Thisisalaboratorytesttodetermineifthedonatedbloodiscompatiblewiththerecipient’sblood.Therearemanydifferentsubgroupsofbloodmarkers,butthetwomostimportantonesaretheABOsystemandRhfactor.

ABOSystem

IntheABObloodsystemtherearetwopossibleRBCmarkers,AandB.ApersonwithanAmarkerissaidtohavetypeAblood.TypeAbloodproducesanti-Bantibodies.ThepresenceofaBmarkergivestypeBbloodandanti-Aantibodies.TheabsenceofeitheranAoraBmarkerresultsintypeOblood,whichcontainsbothanti-Aandanti-Bantibodies.Ifbothmarkersarepresent,thebloodistypeABanddoesnotresultinanyantibodies.

BecausetypeOblooddoesnothaveeithermarkerAorB,itwillnotreactwithanti-Aoranti-Bantibodies.ForthisreasonapersonwithtypeObloodisreferredtoasauniversaldonor.Inanemergency,typeObloodmaybegiventoapersonwithanyoftheotherbloodtypes.Similarly,typeABbloodistheuniversalrecipient.ApersonwithtypeABbloodhasnoantibodiesagainsttheotherbloodtypesand,therefore,inanemergency,canreceiveanytypeofblood.SeeTable12.3.

Table12.3ABOSystem

ABO

BloodType

Antigen

A

Antigen

B

 Antibody

anti-A

 Antibody

Anti-B

A

yes

no

no

yes

B

no

yes

yes

no

O

no

no

yes

yes

AB

yes

yes

no

no

RhFactor

RhfactorisnotasdifficulttounderstandastheABOsystem.ApersonwithRhfactoronhisorherredbloodcellsissaidtobeRh-positive（Rh+）.Sincethispersonhasthefactor,heorshewillnotmakeanti-Rhantibodies.ApersonwithouttheRhfactorisRh-negative（Rh-）andwillproduceanti-Rhantibodies.Therefore,anRh+personmayreceivebothanRh+andanRh-transfusion,butanRh-personcanreceiveonlyRh-blood.

PartII:

TheLymphaticandImmuneSystem

AnatomyandPhysiology

OftheLymphaticandImmuneSystem

Thelymphaticandimmunesystemsconsistofanetworkoflymphaticvessels,lymphnodes,spleen,thymusgland,andtonsils.Thissystemperformsseveralquitediversefunctionsforthebody.First,itcollectsexcesstissuefluidthroughoutthebodyandreturnsittothecirculatorysystem,purifyingitasitpassesthroughthesystem.Fluidwithinlymphaticvesselsisreferredtoaslymph.Lymphiscomposedofwater,whitebloodcells,nutrients,hormones,saltscarbondioxide（CO2）,oxygen（O2）,andurea.Therefore,thissystemassiststhecirculatorysystemintransportingsubstancesthroughoutthebody.Next,itservesasthebody’sprimarydefensesystemagainsttheinvasionofpathogens.Finally,lymphvesselsaroundthesmallintestinesareabletopickupabsorbedfatsfortransport.

LymphaticVessels

Thelymphaticvesselsformanextensivenetworkofvesselsthroughouttheentirebody.However,unlikethecirculatorysystem,thesevesselsarenotaclosedloop.Instead,theyserveasone-waypipesconductinglymphfromthetissuestowardthethoraciccavity.Thesevesselsbeginasverysmalllymphaticcapillariesinthetissues.Excessivetissuefluidentersthesecapillariestobeginthetripbacktothecirculatorysystem.Thecapillariesmergeintolargelymphaticvessels.Thesevesselshavevalvesalongtheirlengthtoensurethatlymphcanonlymoveforwardtowardthethoraciccavity.Thesevessels’finallydrainintooneoftwolargelymphaticducts,therightlymphaticductorthethoracicduct.Thesmallerrightlymphaticductdrainstherightarmandtherightsideoftheneckandchest.Thisductemptieslymphintotherightsubclavianvein.Thelargerthoracicducthastheresponsibilityofdraininglymphfromtherestofthebodyandemptyingintotheleftsubclavianvein.Seefigure12.2.

LymphNodes

Lymphnodesaresmallorganscomposedoflymphatictissuelocatedalongtherouteofthelymphaticvessels.Thesenodes,whicharealsoreferredtoaslymphglands,haveseveralfunction,includingthefollowing:

1.Removingimpuritiesfromthelymphasitpassesthrough

2.Manufacturinglymphocytes

3.Producingantibodiestofightdisease

Oncelymphisdrainedfromthetissue,itisfilteredinthenodetoremoveimpurities.Lymphnodesalsoservetotrapanddestroycellsfromcanceroustumors.Lymphnodesarefoundthroughoutthebody,butareparticularlyconcentratedinseveralregions.Forexample,lymphnodesconcentratedintheneckregiondrainlymphfromthehead.SeeTable12.4foralistofsomeofthemostimportantsitesforlymphnodesandFigure12.3.

Figure12.2LymphaticVessels

Table12.4SitesforLymphNodes

Name

Location

Function

Axillary

Armpits