haemostasis foundation 1-october 2010

8/8/2019 Haemostasis Foundation 1-October 2010

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Haemostasis

h s nagaraja


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Learning outcomes

State hemostasis

Describe hemostatic response

Describe the events in hemostasis Explain the structure and function of platelets

Describe the process of activation of platelets

Describe the intrinsic and extrinsic coagulationmechanism

Explain the anti-clotting systems


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A 35-year old female with

ecchymosis


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A 40-year old male with bleeding

spots


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Inherited Bleeding Disorders

Hemophilia A, B and Von Willebrand Disease

World Hemophilia Day falls

on 17thApril every year and is dedicated

to stepping up awareness of hemophilia

and other bleeding disorders.


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Haemostasis

The process of blood clotting and then the subsequentdissolution of the clot, following repair of the injuredtissue, is termed haemostasis

Haemostasis Normal physiologic process

Maintain blood in fluid, clot free state

Rapid, localized haemostatic plug

At the site of vessel injury


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H

aemostatic response: Primary Phase Blood vessel and platelets

Secondary Phase Coagulation Factors

Good haemostatic response :

i) quick,ii) carefully controlled

iii) localized to damaged region


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Hemostasis, composed of 4 major events that occur

in a set order following the loss of vascular integrity:

1. Vascular Constriction - The initial phase of the

process. This limits the flow of blood to the area ofinjury

2. Platelet plug formation - platelets become activated

by thrombin and aggregate at the site of injury,

forming a temporary, loose platelet plug


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3. Clot Formation - To insure stability of the initially loose

platelet plug, a fibrin mesh (also called the clot) forms

and entraps the plug

If the plug contains only platelets it is termed a white thrombus; if red bloodcells are present it is called a red thrombus

4. Fibrinolysis - The clot must be dissolved in order for

normal blood flow to resume following tissue repair

The dissolution of the clot occurs through the action ofplasmin


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Vascular Spasm

Damage to blood vessel stimulates pain receptors

Reflex contraction of smooth muscle of small blood vessels

Local reflex mechanism

Can reduce blood loss for several hours until other

mechanisms can take over

Vasoconstrictors released from platelets

Only for small blood vessel or arteriole


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PLATELETSSmallest of Formed Elements of Blood

Biconvex Disc; No nucleus; Life span 7-10 DaysNormal Count: 250,000/cu mm

Formed from megakaryocytes in bone marrow

Platelet Factors:

Glycoproteins, phospholipids

Actin, Myosin, Thrombasthenin

Von Willebrand Factor, Factor VIII, Factor V

Thromboxane A2, ADP, PDGF, Fibrinogen , serotonin

2 types of granules; i) Alpha granules contains fibrinogen, thrombospondin, clotting

factors), ii) Dense granules contains calcium, serotonin, ADP, ATP).


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PLATELETS


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Functions of Platelets:

1. Hemostasis Vasoconstriction and Platelet Plug

2. Blood Coagulation Phospholipids

3. For Clot Retraction Contractile Proteins

4. Repairof Ruptured Blood Vessels Growth Factor [PDGF]

5. Release Granules Chemotactic for Neutrophils

6. Defense Mechanism Phagocytic Activity


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The protein fibrinogen is primarily responsible for

stimulating platelet clumping

Platelets clump by binding to collagen that becomes

exposed following rupture of the endothelial lining of

vessels

Upon activation, platelets release adenosine-5'-diphosphate,

ADP and TXA2 (which activate additional platelets),

serotonin, phospholipids, lipoproteins, and other proteinsimportant for the coagulation cascade

In addition to induced secretion, activated platelets change

their shape to accommodate the formation of the plug

PLATELETPLUG


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1. Platelet Adhesion

Platelets stick to exposed collagen underlying damagedendothelial cells in vessel wall


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2. Platelet Release Reaction Platelets activated by adhesion

Extend projections to make contact with each other

Release thromboxane A2, serotonin & ADP activating other platelets

Serotonin & thromboxane A2 are vasoconstrictors decreasing blood flow

through the injured vessel. ADP causes stickiness


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3. Platelet Aggregation Activated platelets stick together and activate new platelets to form a mass

called a platelet plug

Plug reinforced by fibrin threads formed during clotting process


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Platelet Activation

In order for hemostasis to occur, platelets must adhere to

exposed collagen, release the contents of their granules,

and aggregate

The adhesion of platelets to the collagen exposed on

endothelial cell surfaces is mediated by von Willebrand

factor (vWF)

Inherited deficiencies of vWF are the causes of von

Willebrand disease, (vWD)


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The McGraw-Hill


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Shape of platelets:i) stimulated form discoid shape ( 2- 4 Qm)ii) unstimulated state spiny spheric shape


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HAEMOSTATICPLATELET REACTION

VascularInjury

Sub endothelial Collagen

Adhesion

Shape Change

Release Reaction

Vasoconstriction Aggregation

Thrombin

Coagulation

Haemostatic Plug

Fibrin

TXA2, 5HT

TXA2 ADP


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Platelet Aggregation:Membrane Phospholipids

Arachidonic Acid

PGH2

Thrmobaxane A2

Prostacyclin (PGI2)

AGGREGATION

cAMP cytosolic Ca 2+ cAMP cytosolic Ca 2+

Platelets Endothelium

Cyclo oxygenase 1 / 2

Phospholipase C / A2

++


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Blood Clotting

Two pathways

Extrinsic and Intrinsic

Initiated by two distinct mechanisms

Converge on a Common Pathway

Formation of a clot in response to an abnormal vessel

wall in the absence of tissue injury is the result of the

intrinsic pathway

Clot formation in response to tissue injury is the result

of the extrinsic pathway


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Extrinsic Pathway:

A Cellular element outside the blood is needed

Begins with activation of tissue factor

Tissue factor In the walls of blood vessels

Tissue factor binds to factor VII and activates it

Intrinsic Pathway:

Everything necessary for it is in the blood

Activated when plasma comes in contact with constituents ofsub endothelial tissues

Collagen fibrils, negatively charged surfaces

Factor XII, Factor XI, Pre Kalikrein and HMWK are involved


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Factor Trivial Name(s) Pathway

Prekallikrein

(PK) Fletcher factor Intrinsic

High molecular

weight

kininogen

(HMWK)

contact activation cofactor Intrinsic

I Fibrinogen Both

II Prothrombin Both

III Tissue Factor Extrinsic

IV Calcium Both

V Proaccelerin, labile factor Both

VI (same as

Va)Accelerin Both

VII Proconvertin, serum prothrombin conversion accelerator (SPCA) Extrinsic

VIII Antihemophiliac factorA Intrinsic

IX Christmas Factor, antihemophilic factor Intrinsic

X Stuart-ProwerFactor Both

XI Plasma thromboplastin antecedent (PTA) Intrinsic

XII HagemanFactor Intrinsic

XIII Protransglutaminase, fibrin stabilizing factor (FSF), fibrinoligase Both

BLOOD CLOTTINGFACTORS


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Regulatory/Other

ProteinsActivities

vonW

illebrand factor

associated with subendothelial connective tissue; serves as a

bridge between platelet glycoproteinGPIb/IX and collagen

ProteinCactivated to proteinCa by thrombin bound to thrombomodulin; then

degrades factors VIIIa and Va

Protein S acts as a cofactor of proteinC

Thrombomodulinprotein on the surface of endothelial cells; binds thrombin,which

then activates proteinC

AntithrombinIIImost important coagulation inhibitor, controls activities of

thrombin, and factors IXa,Xa,XIa and XIIa

Regulatory Proteins


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ClottingCascade

The intrinsic cascade (which has less in vivo significance than the extrinsic

cascade) is initiated when contact is made between blood and

exposed negatively charged surfaces

The extrinsic pathway is initiated upon vascular injury which

leads to exposure of tissue factor (TF- also identified as factorIII),

a subendothelial cell-surface glycoprotein that binds

phospholipid

The two pathways converge at the activation of factor X to

Xa


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Contact Tissue Factor + VII

XIIIXIIIaa

XIIIXIII

ThrombinThrombin

FibrinFibrin

(strong)(strong)

FibrinogenFibrinogen FibrinFibrin

(weak)(weak)

IXIX

XIXI

XIXIaa

IXIXaa

XXaa

VVaa

XIIXIIaa

ProthrombinProthrombin

TF-VIIa

PLPL

PLPLVIIIVIIIaa

PLPL

XX

Intrinsic Pathway

HKHKaa

Extrinsic Pathway

Common Pathway

TF Pathway

Coagulation PathwaysCoagulation Pathways

Protein C, Protein S,

Antithrombin III


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Intrinsic Pathway

Less significant to hemostasis under normal physiological

conditions than is the extrinsic pathway

Pathway requires the clotting factors VIII, IX, X, XI, and XII

Also required are the proteins prekallikrein (PK) and high-

molecular-weight kininogen (HK orHMWK), as well as

calcium ions and phospholipids secreted from platelets

Initiation of the intrinsic pathway occurs when prekallikrein,high-molecular-weight kininogen, factor XI and factor XII are

exposed to a negatively charged surface - termed the

contact phase


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What is the significance of intrinsic

pathway?

The intrinsic pathway has low significance under normalphysiological conditions

Most significant clinically is the activation of the intrinsic

pathway by contact of the vessel wall with lipoproteinparticles, VLDLs and chylomicrons

This process clearly demonstrates the role ofhyperlipidemiain the generation of atherosclerosis

The intrinsic pathway can also be activated by vessel wallcontact with bacteria


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The McGraw-Hill


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Intrinsic Pathway-

- Is switched on when endothelial cells (i.e. inner-most

lining) of blood vessels are damaged. And this results

in exposure of;

a) Collagen

b) damaged platelets causing the release of

phospholipids


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Extrinsic Clotting Cascade

Activated factor Xa is the site at which the intrinsic and

extrinsic coagulation cascades converge

Pathway is initiated at the site of injury in response to the

release of tissue factor (factorIII) and thus, is also known as

the tissue factor pathway

Tissue factoris a cofactor in the factor VIIa-catalyzed

activation of factor X


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The McGraw-Hill


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Factor VIIa, a serine protease, cleaves factor X to factor Xa in

a manner identical to that of factor IXa of the intrinsic

pathway

The activation of factor VII occurs through the action of

thrombin or factor Xa A major mechanism for the inhibition of the extrinsic

pathway occurs at the tissue factor-factor VIIa-Ca2+-Xa

complex The protein, TFPI and was formerly named anticonvertin,

specifically binds to this complex


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Factor Xa has a role in the further activation of factor VII to

VIIa

Active factor Xa hydrolyzes and activates prothrombin to

thrombin.

Thrombin can then activate factors XI, VIII and V furthering

the cascade

Ultimately the role of thrombin is to convert

fribrinogen to fibrin and to activate factor XIII

toXIIIa

Factor XIIIa (also termed transglutaminase) cross-links fibrin

polymers solidifying the clot


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The common point in both pathways is the activation

of factor X to factor Xa

Factor Xa activates prothrombin (factorII) to

thrombin (factorIIa)

Thrombin, in turn, converts fibrinogen to fibrin

The activation of thrombin occurs on the surface of

activated platelets and requires formation of a

prothrombinase complex [prothrombin activator]


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Final Common Pathway

Prothrombinase and Ca+2

catalyze the conversion of prothrombin to thrombin

Thrombin

in the presence of Ca+2 converts soluble fibrinogen to

insoluble fibrin threads

activates fibrin stabilizing factor XIII

positive feedback cycle


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Clot Retraction & Blood Vessel Repair

Clot plugs ruptured area ofblood vessel

Platelets pull on fibrin threadscausing clot retraction andexpelling serum

Edges of damaged vessel are

pulled together Fibroblasts & endothelial cells

repair the blood vessel


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Role of Vitamin K in Clotting

Normal clotting requires adequate vitamin K

fat soluble vitamin absorbed if lipids are present

absorption slowed if bile release is insufficient

Required for synthesis of 4 clotting factors by

hepatocytes

Produced by bacteria in large intestine


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ANTI - CLOTTING SYSTEMS

Limits clot formation and dissolves clot

Natural anti coagulant mechanisms

Defect in these mechanisms high incidence of

thrombosis [hyper coagulability]


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THROMBIN

PROTEINC ACTIVATOR

THROMBOMODULIN

PROTEINC ACTIVATED PROTEINC

FACTOR Va & VIIIa INACTIVATED

Endothelium

Receptor

1.

PROTEIN S

INACTIVATES INHIBITORS

OFTISSUEPLASMINOGEN

ACTIVATOR [t-PA]

Factor Xa


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2. Anti-thrombinMechanism:

Antithrombin III Plasma and endothelium

Inactivates Thrombin and other clotting factorsHeparin binding to Antithrombin III activation

Prevents spread of clot

FIBRINOLYTIC SYSTEM:

Dissolves clot

Fibrin broken down to fibrin degradation products by Plasmin

Checks and balances coagulation system Prevents intravascular clotting [Thrombosis]

Plasmin formed from inactive precursor Plasminogen

PLASMINOGEN ACTIVATORS


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PLASMINOGEN PLASMIN

FIBRINOGEN FIBRIN

DEGREDATIONPRODUCTSFIBRIN DEGRADATION PRODUCTS

PLASMINOGEN ACTIVATORS

Intrinsic activators:

Kallikrein

XIIa

Extrinsic Activators:

Tissue PlasminogenActivator [t-PA]

Urokinase Type PA [u-PA]

Streptokinase

++

+

+


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Clinical Application

Thrombocytopenia bleeding time increased

Hemophilia hereditary clotting disorder

increased clotting time

Disseminated intravascular clotting

increased bleeding due to depletion of

coagulation factors

Thrombophilia - hypercoagulability


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NORMAL HEMOSTASISNORMAL HEMOSTASIS


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BLOOD VESSELINJURY

VASOCONSTRICTIONPLATELETS

INTRINSIC CLOTTING

EXTRINSIC CLOTTING

ADHESION

AGGREGATION

PLATELET PLUG

HEMOSTATICPLUG

THROMBIN

FIBRIN

PLASMIN

PLASMINOGEN

ANTIPLASMINS

ANTITHROMBINS

NORMAL HEMOSTASISNORMAL HEMOSTASIS

summary

haemostasis foundation 1-october 2010

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