blood coagulation
TRANSCRIPT
Presented by Dr SHARMILA G S
INTRODUCTIONCoagulation is a complex process by which
blood forms clot. It is an important part of hemostasis(the cessastion of blood loss from damaged vessels) wherein a damaged blood vessel wall is covered by a platelet and fibrin containing clot to stop bleeding and begin the repair of damaged vessels.
INTRODUCTIONWhen blood is shed out or collected in a
container,it looses its fluidity and jelly like mass after few min’s.this process is called coagulation or clotting of blood.
The clot is a mesh of thin fibrils entangling the blood cells.these fibrils consist of fibrin .the fibrin is formed from fibrinogen.
BasisBlood flows through intact vessels
Resting state is designed to keep blood flowingArteries: rapid flow. Injury requires a plug
Rapid, localised, controlled. minimise blood flow compromise
Veins: slower, intermittent flow Systemic anticoagulant clot dissolving system
Complex activating and inhibition system
Five componentsVesselsPlateletsCoagulation factors (clot forming) Coagulation inhibitors (clot controlling)Fibrinolysis (clot dissolving)
Haemostasis1. Vasoconstriction2. Platelets activated by thrombin form a
platelet plug3. Fibrin mesh forms via activation of the
coagulation system to strengthen the clot4. Clot dissolution via plasmin5. Normal blood flow past the clot
HISTORYJOHANNES MULLER(180 1-1858) described
fibrin,substance of thrombus.RUDOLF VIRCHOW(1821-1902) named
fibrinogen and it was isolated chemically by PROSPER SYLVIAN DENIS.
ALEXANDER SCHIMOIT suggested fibrinogen fibrin is a
enzymatic process and labelled hypothetical enzyme thrombin and its precurssor prothrombin
ARTHUS in 1890 discovered ca is essential for coagulation.
Platlets ---------1865 & their functions were explained by GIULIO BIZZOZERO in 1882
The theory thrombin is generated by presence of tissue factors was consolidated by PAUL MORAWITZ IN 1905
NOMENCLATUREThe usage of roman numerals rather than
eponyms or systamatic names was agreed upon during annual conferences(starting 1955)of hemostasis experts.
In 1962 consensus was achieved on the numbering of factors I-XII.
This committee evolved into the present day international committee on thrombosis and hemostasis
Assignement of numerals ceasedin 1963.
General conceptsCoagulation factors act as proteases
when activated (serine proteases)Zymogens (inactive eg fibrinogen)
converted to enzymes/proteins by limited proteolysis
Complex formation requiring calcium,phospholipid surface, cofactors
Thrombin converts fibrinogen to fibrin monomer
Fibrin monomer crosslinked to fibrinForms "glue" for platelet plug
FACTORS INVOLVED IN BLOOD CLOTTINGI FIBRINOGENII PROTHROMBINIII THROMBOPLASTINIV CALCIUMV LABILE /PROACCELERIN/ACCELATOR
GLOBULINVI presence has not been provedVII STABLE FACTORVIII ANTIHEMOPHILIC FACTOR
IX CHRISTMAS FACTORX STUART POWER FACTORXI PLASMA THROMBOPLASTIN
ANTECEDENTXII HEGMAN FACTORXIII FIBRIN STABALIZING FACTOR
I FIBRINOGENSoluble plasma protienGlobulin in natureMol.wt is 3,40,000 daltonSynthesized in liver6 polypeptide chainPlasma concen 0.3gm/100mlConverted into fibrin in the presence of
enzyme thrombin
II PROTHROMBINAlpha 2 globulin,plasma protienInactive precursor of thrombinMol.wt is 69,000daltonSynthesized in liver in the presence of vit kConcen in adult is 40mg/100ml,in new born
babies is low, lower in liver diseases
III THROMBOPLASTINTissue factorReleased by extrinsic pathway of formation of
prothrombin activator VI CALCIUM ionic calcium is essential for blood coagulation
V PROACCELERINUnstable factorRequired for formation of prothrombin
activator & thus conversion of prothrombin to thrombin in both extrinsic as well as intrinsic mech of bllod coagulation.
Is consumed during clotting hence absent in serum.
VII STABLE FACTOR/ AUTOPROTHROMBIN IStable protien synthesized in liver in the
presence of vit kRequired for activation of fac x in extrinsic
pathway.It is not consumed during clotting and
therefore present in serum as well as plasma.
VIII ANTI HEMOPHILIC FACTORProtien of beta 2 globulin synthesized in liverRequired for activation of x &formation of
prothrombin activator in intrinsic pathway.Consumed during clotting and therefore
absent from the serum.Congenital deficiency causes classical
hemophilia. Clotting time is prolonged.
IX CHRISTMAS FACTORAlso called plasma thromboplastin
component./auto prothrombin 2Protien synthesized in liver independent of
vit k.It is activated by active factor xi in the
presence of calcium.Essential for formation of prothrombin
activator in intrinsic pathway.Deficiency causes hemophilia B
X STUART POWER FACTORProtein plasma & synthesized in liverActivated by fac ix in the presence of
VIII,Ca,& phospholipids.Activated factor X along with active factor
V ,Ca, and pospholipids forms a complex called prothrombin activator in both pathways.
XI PLASMA THROMBOPLASTIN ANTECEDENTActivated by factor XII required for activation of
factor IX in the presence of calcium in intrinsic pathway.
Deficiency causes hemorrhagic state.
XII HAGEMAN FACTORIs activated to XII a when it comes in contact
wirh negatively charged surface,foreign substance or rough surface.
Its activation in the blood initiates intrinsic pathwayby activating XI to Xia
Activated factor XII also activates prekallikrein to kellikerin which in turn activates XII to XIIa(feedback activations)
XIII FIBRIN STABALIZING FACTOR
Ca2+Plasma protein stabilization
fibrin polymers
PLATLATLET PHOSPHOLIPIDS(PPL)Essential for clotting in the absence of tissue
extract
intrinsic pathway
MECHANISM OF COAGULATIONClot formation is initiated under following
situations1.Trauma to the vascular wall and adjacent
tissues2.Trauma to blood3.Contact of blood with damaged endothelial
cells or collagen or other tissue elements outside the vessel.
the process of coagulation involves a cascade of reactions in which activation of one factor leads to activation of next clotting factor.
The process can be divided into three stepsFormation of prothrombin activatorConversion of prothrombin to thrombinConversion of fibrinogen into fibrin
FORMATION OF PROTHROMBIN ACTIVATOREXTRINSIC PATHWAYINTRINSIC PATHWAY
Extrinsic PathwayExtrinsic Pathway
Tissue traumaTissue trauma
Leakage of Tissue FactorLeakage of Tissue Factor
XX XaXa
Prothrombin activatorProthrombin activator
CaCa+2+2,, factor VII factor VII
CaCa+2+2
Prothrombin Prothrombin ThrombinThrombin(factor II)(factor II)
CaCa+2+2
Intrinsic PathwayIntrinsic Pathway
Blood trauma/ contact with collagenBlood trauma/ contact with collagen
Activation of factor Activation of factor XII, IX, VIIIXII, IX, VIII
XX XaXa
CaCa+2+2
ProthrombinProthrombin activatoractivator
Prothrombin Prothrombin Thrombin Thrombin(factor II)(factor II)
Activation of certain factors (VII, II, X and protein C and S) is essential for coagulation. This activation requires vit K (reduced form)
ThrombinThrombin
FibrinogenFibrinogen Fibrin MonomersFibrin Monomers
Fibrin threadsFibrin threads
CaCa+2+2, factor XIII, factor XIII
EXTRINSIC PATHWAYIt includes following 3 basic stepsRelease of tissue thromboplastin
X XaEffect of activated factor X to form
prothrombin activator
INTRINSIC PATHWAYIT BEGINS IN THE BLOOD ITSELFActivation of factorXIIActivation of factorXIACTIVATION OF FACTOR IXActivation of factor XFormation of prothrombin activator
CONVERSION OF PROTHROMBIN TO THROMBINCaused by prothrombin activator in the
presence of calciumSurface of platelets which forms
platelet plug at the site of injuryThe rate of formation of thrombin is directly
proportional to quantity of prothrombin activator available which in turn is proportional to the degree of trauma to the vessel wall or blood
THROMBINProteolytic enzymeAmt of thrombin produced during clotting of 1ml of
blood is sufficient to coagulate 3 lt of bloodFUNCTIONSConversion of fibrinogen to fibrinPositive feedback role of thrombin accelarate the rate of formation of prothrombin
activator by activating factor VIII,V,XIII.in this way thrombin itself can cause further conversion of thrombin to prothrombin(amplification affect)
Activates protien c(anticoagulant)
Conversion of fibrinogen to fibrin1. Proteolysis Thrombin(proteolytic enzyme) removes
fibrinogen(4 low mol wt peptide chains)
fibrin monomer
2. Polymerization fibrin monomer polymerizes long fibrin threads
which forms reticulum of the clotInitially the clot is weak because the fibrin
threads are not crosslinked with each other
3. stabilization of fibrin polymersFibrin stabalizing factor (XIII) is activated by
thrombin in the presence of calcium,which causes formation of covalent crosslinkages between fibrin threads adding strength to fibrin meshwork.the fibrin meshwork trapes remaining components of plasma and blood cells to form solid mass called clot.
BLOOD CLOT RETRACTIONBlood clot meshwork of fibrin threads
blood cells platelets plasma
The fibrin threads adhere to damaged surface of blood vessels.
Clot begins to contract and squeeze out most of the fluid called serum(plasma- fibrinogen and other clotting factors)---------- 30-60mins
Platelets are essential for clot retraction. platelet thrombosthenin Actin, myosin contractile protiens present in cytoplasm of platlets causes strong
contraction of platlet spicules attached to fibrin fibres
Activated by thrombin and calcium ions
ROLE OF CALCIUM IN BLOOD COAGULATIONREQUIRED FOR PROMOTION OF ALL THE
REACTION except 1st two reactions in intrinsic pathway.
ROLE OF VITAMIN KComplex naphthoquinone deravativeSource absorbed Food bacterial flora gut
liver
ade amt of
bile salts small intestine
In liver synthesis of following factors are dependent on vit k
Coagulant like prothrombinVII,IX,XCirculatory anticoagulant protien
VITAMIN K DEFICIENCYEFFECTSProthrombin time and blood clotting time is
prolonged.CAUSESObstructive jaundiceNew born babiesChronic diarrhoeaSide effects of antibiotics
ROLE OF LIVERPlays a significant role1.Synthesis of procoagulants
V,VII,IX,X,Prothrombin &fibrinogen2.Removal of activated procoagulant3.Synthesis of anticoagulants like
heparin,antithrombin III &protein c
Liver failure causes1.Bleeding disorders due to hypocoagubility of
the blood.2.Uncontrolled extensive clotting inside the
blood vessels
Role of blood vesselsEndothelium plays both anticoagulatry as well as
coagulatory roles.Anticoagulatory roles1.Acts as a barrier between the thrombogenic
subendothelial tissue and the blood.2.Produce heparin and alpha 2 macroglobulin
which are coagulation inhibitors3.Smoothness of uninjured endothelial cells
prevents platelet aggregation4.Produce prostaglandin which opposes platelet
aggregation
Clotting mechanism1.Secreates von willebrands factor it initiates
platlet aggregation and hemostasis.2.Tissue factors released during trauma
initiates the extrinsic pathway
Subendothelial tissueCollagen fibersPlatlet aggregation is initiated when blood
comes in contact with Intrinsic coagulation pathway is initiated
when factor XII is activated.VASCULAR SMOOTH MUSCLECauses vasoconstriction initiated by
mechanical injuries to muscle.
Circulating blood does not clotVelocity of circulation constant velocity. decrease in velocity causes intravascular
clotting.Surface effects of endothelium1.Smoothness of endo lining inhibits platlet
adeshion2.A layer of glycocalyx absorbed to the inner
surface of endothelium being negatively charged repels clotting factors and platlets and thereby prevents clotting.
Intact endothelium acts as a barrier between the thrombogenic subendothelial collageneous tissue and the blood.
CIRCULATORY ANTICOAGULANTSNatural anticoagulant present in the blood
they are1.Heparin2.Antithrombin III3.Alpha 2 macroglobulin4.Protein c
Fibrinolytic mechanismProtein c is naturally occurring
anticoagulant which inactivates factor V ,VII also inactivates an inhibitor of tissue plasminogen activator increasing the formation of plasmin which acts as fibrinolytic.
Removal of activated clotting factors liver plays a important role
ANTIHEMOSTATIC MECHANISMSThe factors which balance the tendency of
the blood to clot invivo constitute the antihemostatic factors. These can be grouped as
1.Factors preventing platelet aggregation2.Factors preventing coagulation3.Factors causing fibrinolysis
Factors preventing platelet aggregationProstacyclinIs a endogenous factor which inhibit platelet
aggregation by inhibiting thromboxane A 2 formation
CIRCULATORY ANTICOAGULANTSHeparin Anti thrombin IIIPROTEIN C
anticoagulantsSubstance which delay or prevent the
coagulation of the bloodTYPESENDOGENOUSEXOGENOUSEndogenous are those present inside the body
naturallyHeparinAntithrombin IIIProtein c
Exogenous anticoagulantHeparinCalcium sequestersVitamin k antagonistDefibrination substance
HEPARINPowerful naturally acting anticoagulantFirst isolated from liverPolysaccharide containing many sulphate
groupsMol wt is 15,000-18,000 dalton SECRETIONSecreated by basophils and mast cells
Mechanism of actionPresent on luminal surface of endothelium it
acts by following mechanismPrevents of activation of prothrombin to
thrombinInhibits the action of thrombin on fibrinogen Facilitates the action of anti thrombin III ,i.e.
acts as its cofactor and thereby inhibits the active forms of clotting factors IX, X,XI,XII
Calcium sequesters/decalcyfing agentsInvitro blood clotting can be prevented by
substance which remove calcium from the blood.these include
Substance which forms insoluble salts with calcium such as sodium citrate and sodium oxalate
Calcium chelators which bind calcium such as ethylene diaminetetraacetic acid(EDTA)
Vitamin k antagonistUsed orally and thus can prevent coagulation
effectively. these includeCoumarian derivatives,e.g. dicoumarol and
warfarinMechanism of actionThese agents occupy vitamin k receptor sites in
the liver and prevent vitamin k to carry out its normal physiological functions.thus these substance inhibit synthesis of vit k dependent factor,i.e. factors VII,IX, AND X
DEFIBRINATION SUBSTANCEDestruction of fibrinogen . These includeMalaysian pit viper venom.Arvin or ancord-purified preparation of snake
venom. It is a glyco protien and is administered by injections.
COLDTemp maintained is 5-10 degree c
Inhibitors: ANTI-coagulantsAntithrombin III
Directly inactivates serine proteasesThrombin and Xa. Also: IXa and XiaPotentiated by heparin
Protein CInhibits (cleaves) the cofactors VIIIa and VaSignificantly decreases the rate of clot
formationNeeds to be activated
Protein S:Enhances activity of protein C
ThrombomodulinActivated by thrombinBinds to thrombin to alter its conformationComplex activates protein C
Tissue pathway factor inhibitorInhibits FVIIa-tissue factor complex
AnticoagulantsToo little or ineffective
Extensive clotToo much
Bleeding
TherapeuticsHeparinActivated protein CTPFI inhibitor
FibrinolysisPrevents excessive fibrin depositionAllows closely coupled with fibrin formationLocalised surface bound phenomenon that is
catalysed by fibrin formation
Components: fibrinolysisPlasminogen -> plasmin
Plasminogen activators
Inactivators of plasminogen
Inhibitors of plasmin
PHYSIOLOGICAL ROLE OF FIBRINOLYSIS SYSTEMPlasmin play following roleCleaning the minute clots of tiny vesselsPromote normal healing processLiquefaction of menstrual clotLiquefaction of sperms in epididymisRole in inflammatory response
TESTS FOR COAGULATIONBLEEDING TIME-the time lapse between the skin prick and
arrest of bleeding is known as bleeding time.Normal rangeBy dukes method-1-6min’sProlonged BT occurs in purpura while its
normal in hemophilia
Clotting timeThe time interval from oozing of blood after
acut or injury till the formation of clot is called clotting time
Normal range is 3-8min’sProlonged in hemophilia
XII
XI
IX
XVIII
Prothrombin (II)
thrombin
fibrinogen fibrin
STABILISED FIBRIN
V, Ca, P/L
VII
Intrinsic pathway
Extrinsic pathway
XIII
APTT
PT
Intrinsic pathway test-PTTActivated partial thromboplastin timeMax activation of contact factorsXII,XI, prekallirein,high mol.wt kinogenMore consistant and reproducableEliminates leangthy contact activation phaseNormal valuesPTT-40-100sec(>120 abnormal)aPTT-25-35sec
Time required for blood to coagulate is called PT
Performed by adding a mixture of calcium and thromboplastin to citrated plasma
As a control, a normal blood sample is tested continuously
PT ratio (PTR) = Patient’s PT Control PT
EXTRINSIC PATHWAY TEST PROTHROMBIN TIME
PROBLEMS WITH PT/PTRThromboplastins are extracts from brain,
lung or placenta of animalsThromboplastins from various manufacturers
differ in their sensitivity to prolong PTMay result in erratic control of anticoagulant
therapy
REFERENCESGuyton and hall; text book of medical
physiology-10th edition.Text book for human physiology for dental
students- indu khuranaWright (1962) “the nomen clature of blood
clotting factors” can med assoc j86 373-4 PMID 14008442
Essential of medical physiology –k sembulingam
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