HEMATOLOGY

PhysiologyUnit3

RegulationofErythrocyteProduction

• Erythropoietin– Secretedbykidney,liver– Actsonbonemarrowtostimulateproductionoferythrocytes

– IncreasedsecretionwhenlessO2 deliveredtokidneys

– Testosteronealsostimulatesreleaseoferythropoietin

Leukocytes

• Producedbybonemarrow• Monocytesandmanylymphocytesundergofurtherdevelopmentoutsidethebonemarrow

Platelets

• Fragmentsoflargecellscalledmegakaryocytes

• Involvedinbloodclotting

• Clotformationcannotoccurwithoutplatelets

BloodCellProduction

Hemostasis

• Preventionofbloodloss(stoppageofbleeding)• Injuriestosmallvessels(arterioles,capillaries,venules)• Immediateresponsetoinjuryisvasoconstriction– Reducesflowtothearea– Pressestogetherthesidesoftheendothelium

• Inducesstickiness• “glues” theendotheliumtogether

• Requires2processes1. Plateletplugformation2. Bloodcoagulation(clotting)

FormationofaPlateletPlug1. Plateletadhesion

– Exposedcollageninconnectivetissue

– vonWillebrandfactor• Secretedbyendothelialcellsandplatelets

2. Triggersplateletactivation– Releasecontentsofsecretory

vesiclesthatactlocally

3. Triggersplateletaggregation– Formationofplateletplug

PlateletPlugLocalization

• Adjacent,undamagedendothelialcellsreleaseprostacyclin(PGI2)– Stronginhibitorofplateletaggregation

• Adjacent,undamagedendothelialcellsalsoreleaseNO– Vasodilator– Inhibitsplateletadhesion,activationandaggregation

BloodCoagulationClotFormation

• Thetransformationofbloodintoasolidgelcalledaclot orthrombus– Consistsmainlyoffibrin

• Clottingoccurslocallyaroundtheplateletplug• Functionistosupportandreinforcetheplateletplugandtosolidifybloodthatremainsinthewoundchannel

ClottingPathwayRoleofThrombin

• Cascadeofeventsleadstotheconversionofprothrombin (plasmaprotein)tothrombin

• Thrombincatalyzesthesplitoffibrinogen toloosefibrin– Fibrinnetworkthenbecomesstabilized

• Thrombinalsostimulatesplateletactivation

ClottingPathway

ClottingPathwayRoleofPlatelets

• Clottingcannotoccurintheabsenceofplatelets

• Activatedplateletsareessentialbecauseseveralofthecascadereactionstakeplaceonthesurfaceofactivatedplatelets

• Activatedplateletsdisplayspecificmembranereceptorsthatbindseveraloftheclottingfactorswhichpermitsthereactionstooccur

ClottingPathway

• Intrinsicpathway– Everythingnecessaryforthispathwayisintheblood

• Extrinsicpathway– Acellularelementoutsidethebloodisneeded

– Tissuefactor• Notaplasmaprotein• Locatedontheouterplasmamembraneoffibroblasts

Thrombin Burst

DissolvingtheClotFibrinolyticSystem

• Afibrinclotisatemporaryfixuntilthebloodvesselisrepaired

• Plasminogen isactivatedtoplasmin

• Plasmin digestsfibrinwhichdissolvestheclot