S5) Haemostasis Flashcards
What are the principles of haemostasis?
- Prevent bleeding
- Prevent unnecessary coagulation (allow blood to flow)
- Make clot
- Control clotting
- Break it down
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What are the essentials for haemostasis?
- Pump: heart, venous valves, calf pump
- Blood vessels are important
- Platelets
- Coagulation factors
- Anticoagulant factors
What are platelets?
Platelets are components of blood produced by megakaryocytes in the bone marrow and bud from cytoplasm
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In three steps, outline platelet adhesion
⇒ Damage to the vessel wall
⇒ Exposure of underlying tissues
⇒ Platelets adhere to collagen via vWF/receptor
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In 3 steps, outline platelet activation
⇒ Platelets secrete ADP, thromboxane, etc to become activated and activate other platelets
⇒ Involved in activation of the clotting cascade
⇒ Provide some coagulation factors by secretion from internal stores
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What does platelet aggregation involve?
Platelet aggregation involves the cross linking of platelets to form a platelet plug
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Identify 6 mediating factors in haemostasis
- Von willebrand factor
- Fibrinogen
- Collagen
- ADP
- Thromboxane
- Thrombin
What is the clotting cascade?
- The clotting cascade is a controlled amplification system involving the activation of precursor proteins to generate thrombin (IIa)
- Thrombin converts soluble fibrinogen into insoluble fibrin
- Fibrin enmeshes the initial platelet plug to make stable clot
Describe the control of the clotting cascade
- Natural anticoagulants inhibit activation
- Clot destroying proteins are activated by the clotting cascade
Identify some coagulation factors
- Fibrinogen
- Prothrombin
- Factor V, VII - XIII
- Tissue factor
Identify some natural anticoagulants
- Protein C
- Protein S
- Antithrombin
- Tissue factor pathway inhibitor
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Describe the process of initiation in the clotting cascade?
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Describe the process of amplification in the clotting cascade?
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What is the role of Von Willebrand Factor?
VWF carries factor VIII and mediates platelet adhesion to the endothelium
Describe changes in the vessel wall during blood clotting
- Vasoconstriction
- Production of vWF (platelet adhesion, carrier of Factor 8)
- Exposure of collagen and tissue factor initiates activation of clotting factors
What is fibrinolysis?
Fibrinolysis is a process which prevents blood clots from growing and becoming problematic by breaking down fibrin clot, a product of coagulation
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What is the clinical relevance of understanding haemostasis?
- Bleeding disorders
- Arterial thrombotic disorders
- Venous thrombotic disorders
- Abnormal blood test results
- Drug therapy for pro- or anti-thrombotic purposes
What are bleeding disorders?
Bleeding disorders are inherited/acquired conditions arising due to abnormality in the vessel wall, platelets or coagulation factors