hematology - mt. sac
TRANSCRIPT
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HEMATOLOGY
PhysiologyUnit3
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RegulationofErythrocyteProduction
• Erythropoietin– Secretedbykidney,liver– Actsonbonemarrowtostimulateproductionoferythrocytes
– IncreasedsecretionwhenlessO2 deliveredtokidneys
– Testosteronealsostimulatesreleaseoferythropoietin
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Leukocytes
• Producedbybonemarrow• Monocytesandmanylymphocytesundergofurtherdevelopmentoutsidethebonemarrow
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Platelets
• Fragmentsoflargecellscalledmegakaryocytes
• Involvedinbloodclotting
• Clotformationcannotoccurwithoutplatelets
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BloodCellProduction
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Hemostasis
• Preventionofbloodloss(stoppageofbleeding)• Injuriestosmallvessels(arterioles,capillaries,venules)• Immediateresponsetoinjuryisvasoconstriction– Reducesflowtothearea– Pressestogetherthesidesoftheendothelium
• Inducesstickiness• “glues” theendotheliumtogether
• Requires2processes1. Plateletplugformation2. Bloodcoagulation(clotting)
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FormationofaPlateletPlug1. Plateletadhesion
– Exposedcollageninconnectivetissue
– vonWillebrandfactor• Secretedbyendothelialcellsandplatelets
2. Triggersplateletactivation– Releasecontentsofsecretory
vesiclesthatactlocally
3. Triggersplateletaggregation– Formationofplateletplug
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PlateletPlugLocalization
• Adjacent,undamagedendothelialcellsreleaseprostacyclin(PGI2)– Stronginhibitorofplateletaggregation
• Adjacent,undamagedendothelialcellsalsoreleaseNO– Vasodilator– Inhibitsplateletadhesion,activationandaggregation
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BloodCoagulationClotFormation
• Thetransformationofbloodintoasolidgelcalledaclot orthrombus– Consistsmainlyoffibrin
• Clottingoccurslocallyaroundtheplateletplug• Functionistosupportandreinforcetheplateletplugandtosolidifybloodthatremainsinthewoundchannel
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ClottingPathwayRoleofThrombin
• Cascadeofeventsleadstotheconversionofprothrombin (plasmaprotein)tothrombin
• Thrombincatalyzesthesplitoffibrinogen toloosefibrin– Fibrinnetworkthenbecomesstabilized
• Thrombinalsostimulatesplateletactivation
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ClottingPathway
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ClottingPathwayRoleofPlatelets
• Clottingcannotoccurintheabsenceofplatelets
• Activatedplateletsareessentialbecauseseveralofthecascadereactionstakeplaceonthesurfaceofactivatedplatelets
• Activatedplateletsdisplayspecificmembranereceptorsthatbindseveraloftheclottingfactorswhichpermitsthereactionstooccur
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ClottingPathway
• Intrinsicpathway– Everythingnecessaryforthispathwayisintheblood
• Extrinsicpathway– Acellularelementoutsidethebloodisneeded
– Tissuefactor• Notaplasmaprotein• Locatedontheouterplasmamembraneoffibroblasts
Thrombin Burst
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DissolvingtheClotFibrinolyticSystem
• Afibrinclotisatemporaryfixuntilthebloodvesselisrepaired
• Plasminogen isactivatedtoplasmin
• Plasmin digestsfibrinwhichdissolvestheclot