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Blood clots

Blood clots. Objectives. Why does blood clot? How does blood clot? Controlling blood clots Pharmaceutical intervention. Why does blood clot?. Virchow’s Triad... Endothelial injury Stress, turbulent flow, scarred valves Increased collagen exposure Altered blood flow

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Blood clots

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  1. Blood clots

  2. Objectives • Why does blood clot? • How does blood clot? • Controlling blood clots • Pharmaceutical intervention

  3. Why does blood clot? Virchow’s Triad... • Endothelial injury • Stress, turbulent flow, scarred valves • Increased collagen exposure • Altered blood flow • Turbulence, due to plaques, aneurysms, sickle-cell • Hypercoaguability • Genetic or acquired • Mutations in factors, MI, heparin, AF, COCP, sickle cell

  4. Howdoesbloodclot? • Vascular Spasm • Platelet Plug Formation • Coagulation Cascade

  5. Vascular Spasm • Damage to arteries = Circular muscle contraction • Caused by - platelet secretions - nociceptor inhibition

  6. Platelet Plug Formation • Damaged endothelium exposes ECM • Platelets adhere via von Willebrand factor • Thromboxane A2 + Serotonin  Vasoconstriction • Thromboxane A2 + ADP  Platelet Aggregation *Primary Haemostatic Plug Thromboxane A2 Clotting factors Fibrin-stabilising factor (XIII) ADP Serotonin

  7. CoagulationCascade Damaged cells... Damaged tissue... TF + Ca2+ Thrombin(IIa) catalyses the conversion of... V Va VIII  VIIIa TF - VIIa VII XII XIIa X Xa +Va XI XIa XIII II IIa VIIIa + IX IXa XIIIa I Ia X Clot retraction

  8. Controlling blood clots • Fibrinolytic system • Dissolves clots via fibrinolysis • Thrombin, XIIa, tissue plasminogen activator (t-Pa) activate plasminogen  plasmin • Plasmin breaks down fibrin and inactivates Ia, IIa, Va, XIIa • WBC/endothelium secrete prostcyclin (inhibit thromboxane A2) • Antithrombin inhibits IIa, Xa, XIIa • PC + Thrombomodulin inactivates Va & XIIIa

  9. Damaged cells... Damaged tissue... TF + Ca2+ Plasmin VII TF - VIIa XII XIIa Antithrombin X Xa +Va XI XIa Activated Protein C XIII II IIa VIIIa + IX IXa XIIIa I Ia X

  10. Anticoagulants • Heparin • Speeds up antithrombin action • Immediate action • 2 types: unfractioned and LMWH • Use for DVT prophylaxis post-op • Warfarin • Inhibits vitamin K reductase, so inactivates clotting factors • 3 days before action • Use as long term anticoagulant, e.g. Prophylaxis, AF, hip surgery, prosthetic heart valves.

  11. Thrombolytics • Used within 12hours of MI, thromboembolic stroke, arterial clots • Streptokinase • Catalyses conversion of plasminogen to plasmin • Increased risk of bleeds and allergic reaction • Alteplase • Cleaves plasminogen into plasmin • Increased risk of stroke

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