The Physiology of The Physiology of coagulationcoagulation

How to clotHow to clot

But not too muchBut not too much

BasisBasis

Blood flows through intact vesselsBlood flows through intact vessels– Resting state is designed to keep blood Resting state is designed to keep blood

flowingflowing– Arteries: rapid flow. Injury requires a plugArteries: rapid flow. Injury requires a plug

Rapid, localised, controlled. Rapid, localised, controlled. minimise blood flow compromiseminimise blood flow compromise

– Veins: slower, intermittent flowVeins: slower, intermittent flow Systemic anticoagulantSystemic anticoagulant clot dissolving systemclot dissolving system

Complex activating and inhibition Complex activating and inhibition systemsystem

Five componentsFive components– VesselsVessels– PlateletsPlatelets– Coagulation factors (clot forming) Coagulation factors (clot forming) – Coagulation inhibitors (clot controlling)Coagulation inhibitors (clot controlling)– Fibrinolysis (clot dissolving)Fibrinolysis (clot dissolving)

HaemostasisHaemostasis

1.1. VasoconstrictionVasoconstriction

2.2. Platelets activated by thrombin Platelets activated by thrombin form a platelet plugform a platelet plug

3.3. Fibrin mesh forms via activation Fibrin mesh forms via activation of the coagulation system to of the coagulation system to strengthen the clotstrengthen the clot

4.4. Clot dissolution via plasminClot dissolution via plasmin

5.5. Normal blood flow past the clotNormal blood flow past the clot

Platelet shape changePlatelet shape change

Pseudopod formationPseudopod formation Interact with adjacent plateletsInteract with adjacent platelets Contract later to consolidate the Contract later to consolidate the

platelet plug in process of clot platelet plug in process of clot retractionretraction

Platelet adhesionPlatelet adhesion

Platelet receptors (integrins)Platelet receptors (integrins)– Glycoprotein Glycoprotein Ib/IXIb/IX– Glycoprotein Ia/IIaGlycoprotein Ia/IIa

Ligands interact with receptorsLigands interact with receptors– Von Willebrand factorVon Willebrand factor

Large (high molecular weight) Large (high molecular weight) multimersmultimers

– collagencollagen

Platelet release Platelet release reaction reaction StimuliStimuli

– Adrenaline, collagen, ADP, thrombinAdrenaline, collagen, ADP, thrombin Release of preformed active substances Release of preformed active substances

from granulesfrom granules– ADP, serotonin, lysozyme,factor V, ADP, serotonin, lysozyme,factor V,

thrombospondin thrombospondin Activate the prostaglandin pathwayActivate the prostaglandin pathway

– Thromboxane A2 via cyclooxygenaseThromboxane A2 via cyclooxygenase Calcium releaseCalcium release Glycoprotein IIb/II activationGlycoprotein IIb/II activation

Platelet

Phospholipid

Arachadonic acid

Endoperoxidases

Thromboxane A2

Calcium flux

Phospholipase A2

Cyclooxygenase

Thromboxane synthase

Phosphodiesterase

Platelet aggregationPlatelet aggregation

Platelet receptorPlatelet receptor– Glycoprotein Glycoprotein IIb/IIIaIIb/IIIa

LigandsLigands– Von Willebrand factorVon Willebrand factor– FibrinogenFibrinogen

IRREVERSIBLE aggregation -> PlugIRREVERSIBLE aggregation -> Plug

Coagulation forms Coagulation forms fibrin meshfibrin mesh Biological amplification system which Biological amplification system which

converts soluble fibrinogen to an converts soluble fibrinogen to an insoluble fibrin meshwork which coverts insoluble fibrin meshwork which coverts the primary platelet plug to a firm, the primary platelet plug to a firm, definitive stable clot.definitive stable clot.

Required local concentration of clotting Required local concentration of clotting factors at site of injuryfactors at site of injury

Surface mediated reactions on exposed Surface mediated reactions on exposed collagen, platelet phospholipid or tissue collagen, platelet phospholipid or tissue factorfactor

General conceptsGeneral concepts Coagulation factors act as proteases Coagulation factors act as proteases

when activated (serine proteases)when activated (serine proteases) Zymogens (inactive eg fibrinogen) Zymogens (inactive eg fibrinogen)

converted to enzymes/proteins by limited converted to enzymes/proteins by limited proteolysisproteolysis

Complex formation requiring calcium,Complex formation requiring calcium,phospholipid surface, cofactorsphospholipid surface, cofactors

Thrombin converts fibrinogen to fibrin Thrombin converts fibrinogen to fibrin monomermonomer

Fibrin monomer crosslinked to fibrinFibrin monomer crosslinked to fibrin Forms "glue" for platelet plugForms "glue" for platelet plug

Cascade effect -> Cascade effect -> amplificationamplification

XIIa

XIa

XI a

IX a

IX a

IX a

IX a

Xa

Xa

Xa

Xa

Xa

Xa

Xa

II a

II a

II a

II a

II a

II a

II a

II a

II a

II a

II a

II a

2x108mol

Fibrin

mesh

1 mol

Coagulation cascadeCoagulation cascade

XII

XI

IX

XVIII

Prothrombin (II)

thrombin

fibrinogen fibrin

STABILISED FIBRIN

V, Ca, P/L

VII

Intrinsic pathway

Extrinsic pathway

XIII

APTT

PT

VIIa

TF X Xa

II (Prothrombin)

IIa (Thrombin)

Va

VIIIa

VaXIa

INITIATION

IXa

AMPLIFICATION

Xa-Va-II

Prothrombinase

Platelet

IXa- VIIa-X

“tenase”

TF IX

VIIa

THROMBIN (IIa) FIBRIN

Fibrinogen -> fibrinFibrinogen -> fibrin

Thrombin cleaves fibrinogen Thrombin cleaves fibrinogen Fibrinopeptide releaseFibrinopeptide releaseFibrin monomersFibrin monomersSpontaneously link to form a loose Spontaneously link to form a loose

polymerpolymerFibrin meshwork is stabilised by Fibrin meshwork is stabilised by

factor XIIIa (activated by thrombin factor XIIIa (activated by thrombin and calcium)and calcium)

Inhibitors: ANTI-Inhibitors: ANTI-coagulantscoagulants Antithrombin IIIAntithrombin III

– Directly inactivates serine proteasesDirectly inactivates serine proteases– Thrombin and Xa. Also: IXa and XiaThrombin and Xa. Also: IXa and Xia– Potentiated by heparinPotentiated by heparin

Protein CProtein C– Inhibits (cleaves) the cofactors VIIIa and Inhibits (cleaves) the cofactors VIIIa and

VaVa– Significantly decreases the rate of clot Significantly decreases the rate of clot

formationformation– Needs to be activatedNeeds to be activated

Protein S:Protein S:– Enhances activity of protein CEnhances activity of protein C

ThrombomodulinThrombomodulin– Activated by thrombinActivated by thrombin– Binds to thrombin to alter its Binds to thrombin to alter its

conformationconformation– Complex activates protein CComplex activates protein C

Tissue pathway factor inhibitorTissue pathway factor inhibitor– Inhibits FVIIa-tissue factor complexInhibits FVIIa-tissue factor complex

AnticoagulantsAnticoagulants

Too little or ineffectiveToo little or ineffective– Extensive clotExtensive clot

Too muchToo much– BleedingBleeding

TherapeuticsTherapeutics– HeparinHeparin– Activated protein CActivated protein C– TPFI inhibitorTPFI inhibitor

FibrinolysisFibrinolysis

Prevents excessive fibrin Prevents excessive fibrin depositiondeposition

Allows closely coupled with fibrin Allows closely coupled with fibrin formationformation

Localised surface bound Localised surface bound phenomenon that is catalysed by phenomenon that is catalysed by fibrin formationfibrin formation

Components: Components: fibrinolysisfibrinolysis Plasminogen -> plasminPlasminogen -> plasmin

Plasminogen activatorsPlasminogen activators

Inactivators of plasminogenInactivators of plasminogen

Inhibitors of plasminInhibitors of plasmin

                                                                         

Effect of plasminEffect of plasmin

Lyses factor V and VIIILyses factor V and VIII Proteolysis of fibrinogenProteolysis of fibrinogen

– Removes small peptidesRemoves small peptides Degradation of fibrinDegradation of fibrin

– Fibrin degradation products (FDP)sFibrin degradation products (FDP)s– D-DimersD-Dimers

Blood Vessel: Blood Vessel: endotheliumendothelium ActiveActive Haemostasis factorsHaemostasis factors

– Von Willebrand factorVon Willebrand factor– Tissue factor – expressed after injuryTissue factor – expressed after injury

Anticoagulant factors Anticoagulant factors – ATIII, protein S, thrombomodulinATIII, protein S, thrombomodulin

FibrinolysisFibrinolysis– Tissue plasminogen activatorTissue plasminogen activator

Haemostatic responseHaemostatic response

1.1. VasoconstrictionVasoconstriction1.1. Initial slowing of blood flow to injured Initial slowing of blood flow to injured

areaarea2.2. Smooth muscle in arteriolesSmooth muscle in arterioles3.3. Vasoactive substancesVasoactive substances

2.2. Platelet primary plug formationPlatelet primary plug formation1.1. Collagen/VWFCollagen/VWF2.2. Glycoprotein Ib/IX and IIb/IIIaGlycoprotein Ib/IX and IIb/IIIa3.3. Aggregation with arachadonic acid Aggregation with arachadonic acid

pathwaypathway

Haemostatic responseHaemostatic response

3.3. Stabilsation of the platlelet plug Stabilsation of the platlelet plug with fibrinwith fibrin

1.1. Tissue factor activation of Tissue factor activation of coagulation cascadecoagulation cascade

2.2. Thrombin burstThrombin burst

3.3. Formation of fibrin meshworkFormation of fibrin meshwork

Haemostasis reactionHaemostasis reaction

4.4. Regulation of fibrin clotRegulation of fibrin clot1.1. Activation of fibrinolysisActivation of fibrinolysis

2.2. Tissue plasminogen activatorTissue plasminogen activator

3.3. Plasmin -> FDPsPlasmin -> FDPs

A test tube is not a A test tube is not a personperson Coagulation in vivoCoagulation in vivo

– TemperatureTemperature– pHpH– CalciumCalcium

That is: hypothermic , acidotic, That is: hypothermic , acidotic, hypocalcaemic patients don’t clothypocalcaemic patients don’t clot

-CARBOXYGLUTAMIC ACID

-carboxy Glu

COO-COO-

COO-

CH

CH2

CHNH3+

COO-

COO-

CH2

CH2

CHNH3+

Glu

O2,CO2

Vit KCarboxylase

VITAMIN K DEFICIENCY

• Almost always hospitalized patients• Require both malnutrition & decrease in

gut flora• PT goes up 1st, 2º to factor VII's short

half-life• Treatment: Replacement Vitamin K• Response within 24-48 hours

FIBRIN FORMATIONA

B

A

B

F XIIIa

T