WEEK 2: HEMOSTASIS AND COAGULATION Flashcards
(37 cards)
What is hemostasis?
Stop bleeding from an injured vessel.
State the 3 components that are involved in hemostasis.
Blood vessel wall
Platelets
Plasma factors: Coagulation factors, anti-coagulation factors
Fibrinolytic factors
Describe the two types of hemostasis.
PRIMARY HEMOSTASIS: Complex defense reaction which involves platelets and vessel wall.
Vasoconstriction and Platelet aggregation.
SECONDARY HEMOSTASIS
Proteolytic cleavage of plasma factors forming BLOOD CLOT.
What is blood clotting?
Transformation of blood from into a solid gel consisting mainly of fibrin.
Describe the endothelial cells
*They form the inner coating of vessel wall.
*They have an anti-platelet and anti-coagulant function.
Describe the anti-platelet function of endothelial cells.
They release prostacyclin and nitric oxide which induce relaxation of perivascular smooth muscles which inhibit platelet aggregation.
Describe the anti-coagulant role of endothelial cells.
*They release Thromboxane A2: Platelet activator and vasoconstriction.
*Von Willebrand factor: The most adhesion molecules of platelets.
Outline the 2 main events of primary hemostasis.
1.Vasular spasm
2.Platelet plug formation
Describe what happens in vascular spasm process of primary hemostasis.
*There is narrowing of blood vessels caused by persistent contraction
-This reduces blood flow through an injured vessel and minimize blood loss.
Describe the process of platelet plug formation.
State the function of ADP and Thromboxane A2 released by activated platelets.
1.Platelet adhesion
*Von Willebrand factor bind to the exposed collagen and the platelets adhere to the binding sites on the vWF.
*The hemostatic foundation of platelet plug is formed.
2.Platelet activation and aggregation
*Collagen activates the platelets.
*Platelets change from their normal disc shaped with smooth surface to SPICKY PROCESSES WHICH HELP THEM ADHERE TO THE COLLAGEN AND OTHER PLATELETS.
3.Platelet aggregation.
*Activated platelets release ADP and Thromboxane A2.
ADP: Causes the surface of nearby circulating platelets to become sticky and adhere to first layer of aggregated platelets.
Thromboxane A2: Directly promote platelet aggregation.
*Enhances it indirectly by triggering the release of more ADP from platelet granules.
Why does the platelet plug not continue to form on the adjacent normal vessel lining?
ADP stimulates release of PROSTACYCLIN and NITRIC OXIDE from the adjacent normal endothelium which inhibit platelet aggregation.
State the main events in secondary hemostasis.
1.Clot formation
2.Clotting cascade
What are the events of clot formation?
To convert fibrinogen to fibrin which is catalyzed by Thrombin.
Fibrin-stabilizing factor, factor XIII then stabilizes the fibrin mesh.
The clotting cascade helps in the conversion of prothrombin into thrombin which is used in clot formation.
What is a clotting cascade?
Sequential reactions of specific factors in the clotting sequence with the aim of activating prothrombin into thrombin.
State the 2 pathways of the clotting cascade.
Intrinsic pathway
Extrinsic pathway
State the difference between the intrinsic pathway and extrinsic pathway.
INTRINSIC PATHWAY
*Slow
*Precipitates clotting within the blood vessel and blood samples in test tubes
*Factor VIII, IX and XII involved.
*Activated by internal trauma
EXTRINSIC PATHWAY
*Fast
*Precipitates clotting in damaged external surface
*Factor VII involved
*Activated by external trauma
Name the pathway that combine both the intrinsic and extrinsic pathway.
Where does it combine the 2?
The common pathway.
At the activation of factor X
State the names for all the factors of the clotting cascade.
Factor I: Fibrinogen
Factor 2: Prothrombin
Factor 3: Tissue thromboplastin
Factor 4: Calcium ion
Factor 5: Labile factor
Factor 6: UNASSIGNED
Factor 7: Stable factor
Factor 8: Antihemophilic factor
Factor 9: Christmas factor
Factor 10: Stuart factor
Factor 11: Plasma thromboplastin antecedent
Factor 12: Hageman factor
Factor 13; Fibrin stabilizing factor
Outline the clotting cascade.
Outline the roles of thrombin.
*Stimulate the conversion of fibrinogen into fibrin.
*It activates factor XIII which stabilizes fibrin meshwork of the clot.
*It enhances the activation of prothrombin via negative feedback.
*It enhances platelet aggregation
*Through positive feedback , platelets secrete PF3 , which stimulates the clotting cascade that results in thrombin activation.
What is clot retraction?
Describe what happens in clot retraction.
*Clot retraction is the process of shrinking a blood clot over a number of days, which brings the edges of the blood vessel wall at the point of injury together to repair the damage.
Platelets shrink the fibrin mesh, pulling the edges of the damaged vessels closer together.
Fluid is squeezed from the clot.
Describe vessel repair.
The aggregated platelets secrete a chemical that helps promote the invasion of fibroblasts from the surrounding connective tissue into the wound area of the vessel.
Fibroblasts form a scar at the vessel defect.
Describe clot dissolution.
What are the 2 products obtained from fibrin dissolution?
Plasminogen is converted to plasmin bt tissue thromboplastin which was trapped in the clot.
Fibrin dissolves and slowly, the fibrins dissolve into fibrinogen and D-dimer.
How the body prevent inappropriate clot formation.
Tissue plasminogen activator quickly activates plasmin to dissolve any small amount of fibrinogen converted to fibrin in absence of any wound.
