FUNCTIONS OF THE COAGULATION SYSTEM FUNCTIONS OF THE COAGULATION SYSTEM ACTION DESIRED RESULT Rapid formation of mechanically sound clot Stop bleeding quickly Prevent clot formation at non- injured sites Prevent thrombosis Gradual replacement of clot with viable tissue Wound healing
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FUNCTIONS OF THE COAGULATION SYSTEM ACTIONDESIRED RESULT Rapid formation of mechanically sound clot Stop bleeding quickly Prevent clot formation at non-injured.
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FUNCTIONS OF THE COAGULATION SYSTEMFUNCTIONS OF THE COAGULATION SYSTEM
ACTION DESIRED RESULT
Rapid formation of mechanically sound clot
Stop bleeding quickly
Prevent clot formation at non-injured sites
Prevent thrombosis
Gradual replacement of clot with viable tissue
Wound healing
BLOOD COAGULATIONBLOOD COAGULATION
Platelet plug
Fibrin clot
PLATELETSPLATELETS
WHAT PLATELETS DOWHAT PLATELETS DO
Stick to damaged blood vessels• requires von Willebrand factor
Spread out to cover damaged area Activate and release contents
• partly blocked by aspirin Aggregate Cause blood vessel constriction Cause retraction of clot to draw wound edges
together
VWF IS A VERY LARGE PROTEINVWF IS A VERY LARGE PROTEINELECTRON MICROSCOPIC IMAGES OF SINGLE MOLECULESELECTRON MICROSCOPIC IMAGES OF SINGLE MOLECULES
VWF UNFOLDS UNDER SHEAR STRESSVWF UNFOLDS UNDER SHEAR STRESSThe faster the blood flow, the stickier it gets
WHAT PLATELETS DO (2)
PLATELET ADHESION TOPLATELET ADHESION TOAREA OF VESSEL AREA OF VESSEL INJURYINJURY
PLATELET PLATELET SPREADINGSPREADING
Patel et al, Blood 2003;101:929-36
PLATELET AGGREGATIONPLATELET AGGREGATION
Tissue damage exposes blood to tissue factor Coagulation cascade: series of enzymatic
reactions leading to thrombin formation• takes place mainly on membrane surface,
eg platelet membrane Thrombin converts fibrinogen to fibrin Fibrin polymerizes and becomes crosslinked
FIBRIN CLOT FORMATIONFIBRIN CLOT FORMATION
Red blood cells trapped in a fibrin mesh
Ubiquitous lipoprotein (part of cell membrane) Initiates physiologic clotting process Highest concentration in brain, mucous
membranes, skin, and immediately outside blood vessels
Forms "hemostatic envelope" Not normally found on endothelial cells lining
Diminished production by bacteria in gut (antibiotic treatment)
Vitamin K antagonists• warfarin (Coumadin)• certain antibiotics
VITAMIN K DEFICIENCYVITAMIN K DEFICIENCY
Associated with many serious/lifethreatening diseases
Circulating blood exposed to excessive amount of tissue factor or other procoagulant
Breakdown of normal regulatory processes Formation of circulating (soluble) fibrin Consumption of clotting proteins and platelets Accelerated fibrinolysis – clots break down too
quickly Bleeding and/or intravascular clotting in severe