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Coagulation Hemostasis &

Fibrinolysis

Hemostasis retains blood in vascular systemif with injury; localizes rxs involved to the siteof injury, repairs & reestablishes blood flow

through injured blood vessel Hemorrhage lack of procogulant; excess of

fibrinolysis

Thrombosis (clot)

lack of fibrinolysis; excessprocoagulant

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Primary hemostasis

Vasoconstriction of damaged blood vesselsplatelet plug (platelet adhesion, secretion,aggregation)

Involves platelets and endothelium Platelet adhesion w/ vascular injury

platelet adheres to subendothelium (collagen,

fibronectin), due to vWF and glycoprotein Ib,IIb & IIIa

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Primary hemostasis

Platelet secretion shape change due to

microtubules; disk spherical w/ pseudopods;

granules go out

Platelet aggregation

PG formation causes plateletaggregation & plt release; arachidonic acid +

cyclooxygenase TXA2 (vasoconstrictor; plt

stimulator) & PGI2 (inhibitor of platelet function)

Clot retraction

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Primary hemostasis

Endothelium

Endothelial injuryvasoconstriction; Factor

XII activation smooth muscle contraction

Normal intact endothelium produces PGI2 to

prevent platelet aggregation w/o coagulant

properties

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Endothelial cells

Assist in platelet activation

Limits coagulation mechanism

Clot dissolution

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Secondary Hemostasis

Clotting factors

Platelets provides surface, plays part in

contact system, XXa, PTT, Vit K dependent

factors in surface of activated platelet,

thrombasthenin (platelet protein) promotes

clot retraction

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Limiting Mechanisms of Hemostasis

Normal blood circulation

Inhibitors (naturally occurring)

Fibrinolysis

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Platelets

60% proteins, 30% lipids, 8% CHO

Minerals, water, nucleotide, glycogen

Glucose

main energy source Function hemostasis, maintenance of

capillary integrity

2/3 in blood; 1/3 in spleen (young)

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Platelets

Cytoplasm:

Chromomere central granular

Hyalomere peripheral non granular

Parts:

Peripheral zone

Sol gel zone

Organelle zone Membranous system

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Peripheral zone DMS; plt adhesion

and aggregation

Glycocalyx made of glycoproteins; reacts w/

vWF

Plasma membrane bilayer, arachidonic acid

Sub-membranous zone receives message

from outside

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Sol-gel zone shape, contractile

Microfilaments (actin, myosin,

thrombasthenin for clot retraction)

Microtubules (tubulinshape)

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Organelle zone

Alpha granules - most numerous, PDGF

Dense bodies ADP, ATP, Ca, serotonin,

pyrophosphate platelet aggregation

Mitochondria ATP synthesis for platelet

metabolism

Lysosomal granules ACP, hydrolytic enzymes

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Membranous System

Dense tubular system from SER holds

calcium, makes PG

Surface connecting system open canalicular

system

system for release of granule

constituents to the outside