HEMOSTASIS/THROMBOSIS II Congenital/Acquired Hemorrhagic Disorders & Their Treatment.
Hemostasis/Thrombosis I - Columbia University to Hemostasis Tuesday, February 24, 2004 – 10:00 am...
Transcript of Hemostasis/Thrombosis I - Columbia University to Hemostasis Tuesday, February 24, 2004 – 10:00 am...
Platelets/Introduction to Hemostasis Tuesday, February 24, 2004 – 10:00 am
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Hemostasis/Thrombosis I
Normal Hemostasis/Thrombosis; Assessment of Clotting System
HEMOSTASIS & THROMBOSIS
• Platelets• Coagulation Cascade• Regulation of Coagulation
Platelets/Introduction to Hemostasis Tuesday, February 24, 2004 – 10:00 am
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CIRCULATORY SYSTEM• Low volume, high pressure system• Efficient for nutrient delivery to tissues• Prone to leakage 2º to endothelial surface
damage• Small volume loss large decrease in
nutrient delivery• Minimal extravasation in critical areas
irreparable damage/death of organism
HEMOSTASISPrimary vs. Secondary vs. Tertiary
• Primary Hemostasis– Platelet Plug Formation– Dependent on normal platelet number & function– Initial Manifestation of Clot Formation
• Secondary Hemostasis– Activation of Clotting Cascade Deposition & Stabilization of
Fibrin• Tertiary Hemostasis
– Dissolution of Fibrin Clot– Dependent on Plasminogen Activation
Platelets/Introduction to Hemostasis Tuesday, February 24, 2004 – 10:00 am
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HEMOSTATIC DISORDERSSuspicions
• Spontaneous bleeding• Prolonged or excessive bleeding after
procedures or trauma• Simultaneous bleeding from multiple sites
HEMOSTATIC DEFECTS
B l e e d i n gP r o b l e m
P l a t e le tD i s o r d e r
C o a g u l a t i o nA b n o r m a l i t y
P e t e c h ia e + -
B le e d in gS i t e s
M u c o u sM e m b r a n e
D e e p T is s u e
T im e o fo n s e t o fb le e d in g
I m m e d ia t e D e la y e d
E c c h y m o s e s/H e m a t o m a s
+ +
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HEMOSTATIC ABNORMALITIES"Screening Tests" (History)
• Dental Extractions• Prior Surgery/Biopsy• Easy bruising• Heavy menses• Deliveries• Blood transfusion
PLATELETS• Anucleate cellular fragments; multiple granules, multiple
organelles• Synthesis controlled by IL-6, IL-3, IL-11, &
thrombopoietin• Circulate as inactive, non-binding concave discs• On stimulation, undergo major shape change• Develop receptors for clotting factors• Develop ability to bind to each other & subendothelium
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PLATELET ACTIVATION
vWFRestingPlatelets Platelet
Adhesion
Initial Thrombin Formation
VIIa-TF
X XaII IIa
IIaTR
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PLATELET ACTIVATION
PlateletActivation
VIIa-TF
X XaII IIa
Platelet Release
TxA2, ADP, Serotonin, Fibrinogen, Thrombospondin
VIIa-TF
X XaII IIa
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PLATELET PLUG FORMATION
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COAGULATION CASCADEGeneral Features
• Zymogens converted to enzymes by limited proteolysis
• Complex formation requiring calcium,phospholipid surface, cofactors
• Thrombin converts fibrinogen to fibrin monomer
• Fibrin monomer crosslinked to fibrin• Forms "glue" for platelet plug
Platelets/Introduction to Hemostasis Tuesday, February 24, 2004 – 10:00 am
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COAGULATION CASCADE
THROMBIN• Serine protease• Cleaves fibrinogen to fibrin• Activates V to Va, VIII to VIIIa• Activates platelets-cleaves thrombin receptor• Activates XIII to XIIIa• In presence of thrombomodulin activates
Protein C to APC
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COAGULATION CASCADE
Platelet Release
TxA2, ADP, Serotonin, Fibrinogen, Thrombospondin
VIIa-TF
X XaII IIa
VIIa-TF
IX IXa
VIII VIIIa
V Va
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Tenase/Prothrombinase complex assembly
VIIIa RVIIIa/IXa
X Xa
Va/XaVa R
II IIa
FIBRIN FORMATIONA
B
A
B
F XIIIa
T
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VITAMIN K DEPENDENT CARBOXYLASE• Post-translational modification• Factors II, VII, IX, X; proteins C & S• Converts 1st 7-12 glutamic acids toγ-carboxyglutamic acid
• Confers calcium binding and lipid binding on these proteins
• Without vitamin K, secrete des-γ-carboxyglutamic acid containing proteins(inactive in coagulation)
γ -CARBOXYGLUTAMIC ACID
γ-carboxy Glu
COO-COO-
COO-
CH
CH2
CHNH3+
COO-
COO-
CH2
CH2
CHNH3+
Glu
O2,CO2
Vit KCarboxylase
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PLATELET FUNCTION STUDIES
• Bleeding Time• Platelet Count• Platelet Aggregation Studies
BLEEDING TIME vs. PLATELET COUNT
050
100150200250300350400
3.5 4 4.5 5 5.5 7 9 12 15 25 30
Minutes
Plat
elet
cou
nt (x
100
0)
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COAGULATION CASCADE
Clotting Tests• Recalcification times• Blood collected in sodium citrate, a weak
calcium chelator• Amount designed to drop calcium
concentration to < 1 mM• At that level, blood won’t clot spontaneously• RBC’s & platelets centrifuged off, leaving
plasma (unclotted liquid portion of blood)
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Prothrombin Time
• Mixture of: – 50% patient’s platelet poor plasma– 25% Mixture of Tissue Factor & phospholipid
species– 25% Calcium chloride (to bring final calcium
concentration to c. 3-5 mM)– Time to clot formation measured
COAGULATION CASCADE
Va/Xa/PLVa/Xa/PL
VIIa/TFVIIa/TF
TF FVII
FGF
FVIIaCa+2
V VaT
Ca+2FXFXa Ca+2
Ca+2PTTCommon Pathway
Middle Components
EXTRINSIC PATHWAY
ProthrombinTime (PT)
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aPTT (activated partial thromboplastin time)
• 50% patient’s platelet-poor plasma• 25% mixture of phospholipid & surface active
agent (Celite, Kaolin)• 25% Calcium Chloride to bring calcium
concentration to 3-5 mM• Time to clot formation measured
COAGULATION CASCADE
Va/Xa/PLVa/Xa/PL
VIIIa/VIIIa/IXaIXa/PL/PL
FXIIFXIIa
FGF
HMWKFXIFXIa
Ca+2FIXFIXa Ca+2
VIII VIIIaT
V VaT
Ca+2FXFXa Ca+2
Ca+2PTTCommon Pathway
Middle Components
Surface Active Components
INTRINSIC PATHWAY
aPTT
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COAGULATION CASCADEContact Phase
F XII
F XIIa
HMWK
F XI
F XIa
Prekallikrein
Kallikrein
COAGULATION CASCADEIntermediate Phase
IXa/VIIIa/PL
VIIa/TF/PLF IX
F IXa
Ca+2
Ca+2
Ca+2
XIa
F VII/TF
F VIIa/TF
Ca+2
VIII VIIIa +T
F XF Xa
Tenase Complex
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COAGULATION CASCADECommon Pathway
IXa/VIIIa/PL VIIa/TF/PL
F Xa
F XF X
V Va + Xa/Va/PL
PT
TFibrinogen
Fibrin monomer
Prothrombinase ComplexCa+2
Ca+2 Ca+2
CLOTTING ASSAYSSpecific factors/Inhibitors
• Deficiency states of every clotting protein described• 50% of any clotting factor will yield normal PT
and/or aPTT• Mix 1/2 patient plasma with 1/2 factor deficient
plasma; then perform PT and/or aPTT• Factor deficient plasma with missing factor will
prolonged clotting time; all others WNL• If more than one clotting assay prolonged, implies
inhibitor to clotting protein