Physiology of coagulation

1. Applied Sciences Lecture Course Physiology of coagulation Mahesh Nirmalan MD, FRCA, PhD Consultant, Critical Care Medicine Manchester Royal Infirmary

2. Hemostasis • Blood must be fluid • Must coagulate (clot) at appropriate time • Rapid • Localized • Reversible Thrombosis…inappropriate coagulation

3. Natural heparin like molecules that inactivate thrombin Fibrinogen → Fibrin Thrombin • Thrombomodulin • When bound to thrombin • Activates Protein C • Inactivates clotting factors Fibrinolysis Breakdown of fibrin Plasmin (Plasminogen) tPA Anti-thrombotic mechanisms Thrombosis

4. Clotting or thrombosis Rudolph Virchow

5. COAGULATION PROTEINS Endothelium Platelets Components of haemostasis

6. Endothelium

7. ANTICOAGULANT PROCOAGULANT Plasminogen activator inhibitors Plasminogen activators Fibrinolytic inhibitors Protein C→ Activated Protein C Thrombin/Thrombomodulin Thrombin/Thrombomodulin Tissue Factor inhibitors Prostacyclin Von Willibrand Factor Tissue Factor

8. Pro-coagulant role of the damaged endothelium • Synthesises tissue factor when damaged • Acquires the tissue factor from macrophages • Tissue factor, when bound to VIIa is the major activator of the extrinsic pathway • Major site for the synthesis and storage of vWF • Increased Platelet adhesion • Carrier protein for Factor VIII • Inhibition of Fibrinolysis • Thrombin activated fibrinolytic inhibitor • Plasminogen activator inhibitor

9. Platelets • Anucleate sub-cellular fragments • Arise from megakaryocytes in the marrow • Normal count: 200-400 thousand/μl • Several surface receptors • Activated by contact with extra-cellular matrix • Aggregation to form a platelet plug • Stabilisation by the formation of a fibrin clot

10. Platelets-2 • Contact with collagen • Swelling and pseudopod formation • Contractile proteins contract forcefully • Release of platelet granules • Increased adhesion • Adhere to collagen and vWF • ADP and Thromboxane production • Cascade of events lead to a platelet plug

11. Anti-platelet agents • Inhibition of COX mediated Thromboxane synthesis: Aspirin • ADP receptor inhibition: Clopidogrel • Platelet phosphodiesterase inhibition: Dipyridamole

12. Haemostasis • Primary • Vasoconstriction • Platelet plug formation • Secondary • Coagulation • Organisation of clot

13. www.homepage.montana.edu/~awmsg/Coagulation.ppt

14. www.homepage.montana.edu/~awmsg/Coagulation.ppt

15. Secondary haemostasis&Coagulation proteins

16. Newer models of coagulation: beyond the scope of this lecture Traditional models of coagulation

17. Fibrinogen Fibrin

18. Thrombin Fibrinogen Fibrin

19. Factor 2 Produced in the Liver Vit K dependant Post translational modification Prothrombin (II) Xa Va Thrombin (IIa) Fibrinogen Fibrin

20. Extrinsic Pathway TF Prothrombin VIIa Xa Va Thrombin Fibrinogen Fibrin

21. Intrinsic pathway XIIa Extrinsic Pathway XIa TF Prothrombin IXa VIIa VIIIa Xa Va Thrombin Fibrinogen Fibrin

22. Intrinsic pathway XIIa Extrinsic Pathway XIa TF Prothrombin IXa VIIa VIIIa Xa Va Thrombin Unstable clot Fibrinogen Fibrin XIIIa Stable clot Fibrin

23. APTT/ACT Prothrombin time + + Intrinsic pathway XIIa Extrinsic Pathway XIa TF Prothrombin IXa VIIa VIIIa Xa Va Soft clot Thrombin Fibrinogen Fibrin XIIIa Hard clot Fibrin

24. Hemophilia A Deficiency or nonfunctional VIII X linked recessive Females: asymptomatic careers 1:5-10,000 male births Hemophilia B Deficiency or nonfunctional IX X linked recessive Females: asymptomatic careers 1:20-30,000 male births

25. Physiologic Inhibitors of coagulation • Antithrombin III • Activated Protein C + protein S • Inactivates Va and VIIIa (via proteolysis) • Thrombomodulin (EC glycoprotein) • Binds to thrombin • Decreases ability to produce fibrin • Increases ability to activate Protein C

26. Heparin • Naturally occurring mucopolysaccharide • Very acidic • A heterogeneous group of substances • Inactivates thrombin and Xa • High affinity bonding with Anti-thrombin-3 • Neutralised by Protamine • Chemical neutralisation • PT and APTT will be prolonged • Monitored through APTT • More functional tests available: Heparinase test

27. Role of vitamin K • Some clotting factors require a post-translational modification before they are active in clotting • These factors are II, VII, IX, X, proteins C and S • This PTM involves the addition of a COO- to certain Glutamate residues in the clotting factors • Gamma-carboxyglutamate residues • Essential for Ca2+ binding • This PTM requires vitamin K

28. Inhibitors of coagulation • Vitamin K antagonists (in vivo only) • Ca chelators (in vitro only) • EDTA • Citrate • Oxalate • Heparin (in vivo and in vitro)

29. Disseminated intravascular coagulation • Uncontrolled coagulation • Concurrent Fibrinolysis • Depletion of all clotting factors→bleeding • Consumptive coagulopathy • Increase in products of fibrin breakdown • Severe sepsis, massive trauma/tissue breakdown, burns, pancreatitis, obstetric (placental abruption), amniotic fluid embolism

30. Clot removal

31. Fibrinolysis Plasmin Fibrin Fibrin degradation Products (FDP)

32. Thrombolytic agents • Streptokinase • Urokinase • tPA • Alteplase: Recombinant natural tPA • MI, acute stroke, PE Fibrinolysis Plasminogen tPA Plasmin Fibrin Fibrin Split Products (FSP)

33. Inhibitors of fibrinolysis Plasminogen activator inhibitors (PAIs) In excessive bleeding DIC after CPB Bleeding after prostatectomy • Tranexamic acid • α2-antiplasmin (serpin) Should be used only after functional assays of clotting: Thrombo Elasto Graphy (TEG) Poor clotting or excessive clot lysis

34. Clotting studies • FBC: Platelet count & platelet function studies • PT • APTT • Fibrinogen level • FDP • D-Dimers • Individual factor assays • Anti-Xa activity : for monitoring LMWH

35. Figures obtained from freely accessible internet sites. No personal or Institutional credit is claimed.

36. ??