bleeding time 1

7/28/2019 Bleeding Time 1

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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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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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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

bleeding time 1

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