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TRANSCRIPT
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Week 5: Primary Hemostasis
Hemostasis
Platelet function
Platelet anatomy
Megakaryocyte
Platelet kinetics
Platelet count
Aggregation studies
Von Willebrands
Bernard-Soulier
Aspirin (salicylate)
Vascular problems
Allergy
Viral infection
Collagen disorders
Vitamin C deficiency
Ehlers-Danlos
Render-Osler-Weber
telangiectasia
Petechiae, ecchymoses
Bleeding time
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Vascular Injury
Serotonin and thrombaxane A2 (TxA2) for
vasoconstriction
Prostacyclin PGI-2 for arteriole relaxationto increase blood flow
Exposure of basement membrane and
collagen (negatively charged surface)
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Inside of a vessel SEM x 2,500
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Process of Hemostasis
Vascular injury
Platelet adhesion and activation
Platelet aggregation (1o hemostatic plug)
Fibrin formation via cascade (2o
hemostasis)
Clot retraction (thrombasthenin)
Fibrinolysis and healing
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Role of Platelets
Surveillance for
vascular integrity
Formation of 1ohemostatic plug
Activation of 2o
hemostasis
Healing
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Platelet Formation
Megakaryoblast undergoes endomitosis
Intermiediate stage promegakaryocyte
without granules
Megakaryocyte (2N to 64N) with over
100 diameter
IL3, GM-CSF, thrombopoietin
20% of platelet stored in spleen
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Platelet
2 - 4 diameter
Round or oval
Hyalomere - clear peripheral zone
Granulomere - highly stained area with
granules
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Platelet Anatomy
Peripheral zone with glycoproteinreceptors
Structural zone with contractilemicrotubules (thrombasthenin)
Organelle zone with granules
Membrane with open cananicular andtubule systems for increased surface areaand rapid release
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Electron micrograph of a platelet x 25,000
Longitudinal peripheral microtubule (brown), endoplasmic reticulum
(blue), mitochondria (green), glycogen (black)
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Platelet Function
Adhesion to basement membrane or collagen withvWF and GP-Ib
Activation
Shape change from discoid to distorted
Exposure of GP-IIb/IIIa and other receptors
TxA2 synthesis (cyclo-oxygenase dependent)
Membrane phospholipid Arachidonic acid
Arachidonic acid TxA2 and prostaglandins
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Platelet Function:
Glycoprotein Group or Gene Families Integrins
Leucine rich glycoprotein family
Selectin family
Quadraspanin family
Immunglobulin supergene family
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Integrins
Integral to membrane
Ca++ dependent GPIIb/IIIa most abundant
Cell-cell or cell-substrata interaction
Receptor to Fib, vWF, vitronectin,
fibronectin
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Leucine Rich GP Family
Adhesion to subendothelial collagen (COL)
mediated by vWF by transmembrane
complex GPIb/IX Stabilizes PLT membrane by interaction
with cytoskeleton
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Selectin Family
GMP-140 mediates adhesion of neutrophils
and monocytes to PLT
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Quadraspanin Family
Plasma membrane protein p24/CD9
interacts with GPIIb/IIIa, modulating
adhesion molecules Leads to Ca++ increase and subsequent PLT
activation and aggregation
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Immunoglobulin Supergene Family
Functional role unclear
Has role in cellular interactions
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Platelet Activation
1o aggregation with agonists: ADP, epinephrin,serotonin, PF4 (anti-platelet)
Release or secretion facilitated by TxA2
Dense body for 2o aggregation andvasoconstriction (ADP, Ca++, serotonin)
-granule for heparin neutralization and clot
Platelet derived growth factor (PDGF) forhealing
Retraction
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Signs and Symptoms of 1o
Hemostasis Problems Ecchymoses
Petechiae
Mucus membrane bleeding
Hematoma
Prolonged bleeding after minor surgery
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Hereditary Vascular Problems
Hereditary (spider) telangiectasis (Osler-
Rendu-Weber): dilated superficial
capillaries Ehlers-Danlos: collagen disorder
Marfan syndrome: connective tissue
Osteogenesis imperfecta
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Acquired Vascular Problems
Senile purpura (Batemans): altered
connective tissue support
Cushing syndrome: metabolic
Scurvy: abnormal collagen
Allergy: vascular inflammation
Viral infection
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Bleeding Time
For vascular and platelet functions
Duke (1910) on earlobes
Ivy (1941) on arm with 1mm x 3mm
incision
Mielke (1969) with 1mm x 10mm template
1980s: disposable devices (e.g., Simplate,
Surgicutt)
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Bleeding Time
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Quantitative Platelet Disorders
Thrombocytopenia
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About Thrombotic Thrombocytopeneic
Purpura (TTP) Disorder of systemic platelet aggregation in
microvasculature
Stimulus: unusually large vWf
In children: likely to be deficiency in vWfmetalloproteinase to break down vWf
In adults: vWf metalloproteinase inhibited by
autoantibodies Low PLT count, intravascular hemolysis, RBC
fragmentation, high LDH
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Quantitative Platelet Disorders
Thrombocytopenia due to decreased production
Aplastic anemia (e.g., Fanconis)
Fibrosis
Acute leukemia Megaloblastic anemia
Hereditary (e.g., May-Hegglin, Wiscott-Aldrich,Bernard-Soulier)
Splenic sequestration
HELLP syndrome (hemolysis, elevated liver enzyme,low PLT) in pre-eclampsia
Dilution (massive transfusion)
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Platelet Satellitosis in EDTA
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Quantitative Platelet Disorders
Thrombocytosis
Primary with dysfunctions (e.g., CML,
ET)
Post splenectomy: also see HJ, etc.
Hemolytic anemia
Acute hemorrhage and surgery
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Pseudo Thrombocytosis
Red cell abnormalities
HJ bodies
Clumped Pappenheimer bodies nRBC
Malaria
Microspherocytes and schistocytes
White cell abnormalities
Unlysed WBC
WBC fragments and necrobiotic cells
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Platelet Count
Rees-Ecker with brilliant cresyl blue
Brecker-Cronkite with ammonium oxalate
Unopette: similar to BC
Electronic counters
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Qualitative Platelet Disorders
Berhard-Soulier: GP-Ib deficiency, adhesionproblem
Von Willebrands: vWF deficiency, adhesionproblem
Glanzmanns thrombasthenia: GP-IIb/IIIadeficiency, aggregation problem -- cannot bindvWF and Fib
Storage pool disease: dense body defect, secretionproblem
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Qualitative Platelet Problems
Aspirin: inhibits cyclo-oxygenase (COX),secretion problem, no TxA2
Plavix (Clopidogrel) inhibits ADP receptor Other medications affect GPIIa/IIIb
interaction with Fib
Uremia, secretion problem Gray platelet syndrome: -granule defect
Hypofibrinogenemia
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Aggregation Studies
ADP
reversible 1o wave
if ADP is released, then 2o wave
abnormal with aggregation and release problems
Epinephrin
similar to ADP
Collagen
direct release so only one wave of aggregation
Ristocetin
antibiotic
aggregation only with vWF and GP-Ib
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Platelet Aggregometry
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Platelet
Aggregation