HAEMOSTASIS AND THROMBOSIS Regulation of coagulation Vessel wall injury Vasoconstriction, local blood pressure drop Activation of platelets Activation of plasmatic coagulation Activation of fibrinolysis Regulation by inhibitors and endothelial cells Formation of fibrin-platelet-thrombus Wound closure / cessation of bleeding Tissue regeneration / wound healing Disturbed coagulation may lead to bleeding, thromboembolism and/or impaired wound healing!

What is haemostasis? Coagulation Fibrinolysis Maintains blood in a fluid state in circulation and provides defence mechanism against bleeding when injury occurs Vasoconstriction of the damaged vessel Coagulation Fibrinolysis Platelet plug formation primary haemostasis Key messages: Haemostasis is a physiological mechanism – normal state of blood and defense Vasoconstriction: In order to minimize blood loss. Vasoconstrictors produced by endothelium Adrenergic vasoconstriction (epinephrine) Platelet plug formation: Caused by interaction between platelet and blood vessel wall/wound Caused by effect of the functions of platelets (thrombocytes) Platelet glycoproteins: GP Ib binds to vWF lack of Bernard Soulier GP Ia/IIa binds to collagen GP IIb/IIIa binds to fibrinogen, vWF and other lack of Glanzmann For normal primary haemostasis the following is needed: normal vWF, amount and function adequate number and function of thrombocytes, see above normal activation of thrombocytes, can be blocked with thrombocyte function inhibitors (ASA, dipyridamol, clopidogrel) normal aggregation of thrombocytes normal collagen pharmacological interaction: heparin inhibits binding of GP Ib binding to vWF GP IIb/IIIa inhibitors inhibits binding of GP IIb/IIIa to fibrinogen and vWF ASA, dipyridamol, clopidogrel metabolic inhibition of activiation of thrombocytes Fibrin clot formation secondary haemostasis Fibrinolysis tertiary haemostasis

What is the function of thrombin? Necessary for haemostasis Activates platelets Activates FVIII and FV Activates FXIII necessary for the formation of fully stabilized fibrin clots/plugs Activates FXI (feed-back loop leading to more thrombin formation via FIX) Activates TAFI (thrombin activatable fibrinolysis inhibitor) TAFI (carboxypeptidase) prevents the conversion of GLU-plasminogen into LYS-plasminogen

Summary Initiation Amplification Propagation TF complexes with FVIIa, which activates FX to FXa FXa generates small amount of thrombin on surface of TF-bearing cells with FVa as co-enzyme FVIIa also activates FIX to FIXa Amplification Thrombin activates platelets Thrombin cleaves FVIII from vWF and FVIII is activated to FVIIIa Thrombin activates FXI and FV Propagation FIXa-FVIIIa complex generates FXa on the surface of activated platelets This FXa generates a huge thrombin burst Thrombin converts fibrinogen to fibrin

Platelet Function Adherence Only Aggregation & Release Direction of Blood Flow

Bernard-Soulier Syndrome Platelet Adherence von Willebrand Disease vWF Gp Ib vWF Bernard-Soulier Syndrome Gp Ib vWF vWF

Platelet Release Function Wiskott-Aldrich syndrome ADP Hermansky-Pudlak syndrome ß-thromboglobulin Platelet factor 4 DenseGranule Platelet-derived Growth Factor Alpha-granule Gray platelet syndrome Lysosome Fibrinogen Chédiak- Higashi anomaly Factor V Hydrolase

Platelet Aggregation IIIa IIIa IIIa Release Defects Thrombasthenia ADP vWF IIIa IIb Gp Ib Release Defects Dense Granule ADP Thrombasthenia Fibrinogen E D IIIa IIb IIIa IIb Afibrinogenemia

Antithrombotic Properties of the Endothelium Anti-platelet properties Healthy endothelium does not bind platelets Produce PGI-2 (prostacyclin) and NO (Nitric Oxide), which inhibit platelet binding Produce ADP-ase which counters the platelet aggregating effects of ADP

Antithrombotic Properties of the Endothelium (cont Antithrombotic Properties of the Endothelium (cont.) Anticoagulant properties Produce Heparin-like proteoglycans which activate anti-thrombin Produce Thrombomodulin which make a complex with thrombin (TM.T complex ) and activates protein C , Produce tPA which activates fibrinolysis by activating plasminogen to plasmin

Prothrombotic Properties of the Endothelium Synthesis of von Willebrand factor Release of tissue factor Production of plasminogen activator inhibitors (PAI) Membrane phospholipids bind and facilitate activation of clotting factors via Ca++ bridges

Procoagulant Anticoagulant

Procoagulant Anticoagulant

Virchow’s Triad Endothelial injury Abnormal blood flow Pathogenesis of a Thrombus Endothelial injury Abnormal blood flow Hypercoagulability Genetic acquired

Intrinsic pathway XIIa Extrinsic Pathway XIa TF Prothrombin IXa VIIa VIII VIIIa Xa Va V Soft clot Thrombin Fibrinogen Fibrin XIIIa Hard clot Fibrin

Folate and Homocysteine Metabolic Pathways