Haemostasis Flashcards
What cell components are involved when you form a clot?
1 - Platelets
2 - Von Willebrand Factor
3 - Coagulation factors
Why blood clots not spread past the site of injury?
Natural anticoagulants
What blood system is responsible for the blood clot vanishing 1 week after the injury?
Fibrinolytic system
What sorts of things can cause platelets and coagulation factors to become activated to form a clot?
Abnormal vessel surface
Physiological activator
Heparans and prostacyclin are both found within the endothelial surface of blood vessels to prevent what from happening?
Clotting
How do platelets react to vessel damage?
They are attracted to the non-sticky surface of the sub-endothelium which has been exposed by the damage
The platelets stick to the collagen on the surface of the subendothelium
What are the roles of platelets in haemostasis?
1 - Adhere
2 - Activation
3 - Aggregation
What are the 3 major steps of haemostasis?
1 - Vasoconstriction
2 - Temporary blocakge by a platelet plug
3 - Coagulation
What molecules are responsible for causing vasoconstriction following damage to a vessel?
Paracrines
Once platelets have adhered to the collagen on the exposed sub-endothelium surface, what happens next?
Cytokines are released which reinforce vasoconstriction and attract more platelets which aggregate and form a platelet plug
How does the formation of the blood clot begin?
Tissue factor attaches to collagen and sets off the coagulation cascade
Once the coagulation cascade has been activated, what happens?
1 - Thrombin formation
2 - Thrombin converts fibrinogen to fibrin
3 - Fibrin reinforces the platelet plug already formed
What is the final product of the coagulation cascade?
Fibrin
How are blood clots dissolved once the tissue has been repaired?
Plasmin dissolves the fibrin in the blood clot
What is the 1st enzyme activated in the coagulation cascade in the intrinsic pathway?
Factor XII
What is the 1st enzyme activated in the coagulation cascade in the extrinsic pathway?
III (Tissue Factor)
Tissue Factor activates which enzyme to begin the extrinsic coagulation cascade?
VII
What is the common goal of the extrinsic and intrinsic pathways of the coagulation cascade?
To produce Thrombin
What is the function of Thrombin?
Convert fibrinogen into fibrin
What enzyme converts fibrin into a more stable version that stabilizes the clot?
XIII
How is plasmin (breaks down fibrin) formed?
Thrombin + Tissue plasminogen activator
What is a breakdown product of fibrin?
D-dimer
What can D-dimer be used for?
Detection of:
DVT
Pulmonary Embolism
What are the 2 mechanisms that prevent clots from growing indefinitely?
1 - Inhibition of platelet adhesion
2 - Inhibition of coagulation cascade & fibrin production
What are the three anticoagulants produced by the body?
1 - TFPI
2 - Antithrombin III
3 - Protein C & S
If clots have formed in the body due to diseases (e.g. MI’s, DVT’s, PE’s), what are the medication options for dissolving the clots?
1) Fibrinolytic/Throbolytic drugs
2) Antiplatelets
3) Anticoagulants
What are examples of thrombolytic drugs?
1) Streptokinase
2) Alteplase (tissue plasminogen activator)
What are examples of anticoagulant drugs?
1) LMWH
2) Warfarin
What are examples of antiplatelet drugs?
1) Aspirin
2) Clopidogrel
3) Ticagrelor
What is the target of thrombolytic/fibrinolytic drugs?
Fibrin
What is the action of aspirin?
Inhibits cyclooxygenase (COX)
What is the action of clopidogrel and ticagrelor?
ADP receptor inhibitor
What is the mechanism of action of warfarin?
Prevents prothrombin production by antagonising Vitamin K
What is the mechanism of action of LMWH?
Binds to antithrombin making it more active
Blocks Xa coagulation factor
What are the 5 DOAC’s most commonly used?
1 - Rivaroxaban
2 - Edoxaban
3 - Apixaban
4 - Dabigatran
What are the 2 main actions of the DOAC’s?
1 - Thrombin inhibition
2 - Factor Xa inhibition
