Hemostasis. Coagulation vs anticoagulation

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1 Hemostasis is a process of forming clots in the wall of damaged blood vessels and preventing blood loss while maintaining blood in fluid state within the vascular system. Coagulation vs anticoagulation Dr. Gabriella Kékesi 21. Primary hemostasis. Elaborate the role of primary hemostasis, enlist and characterize the significance of its major processes (vasoconstriction, activation and aggregation of platelets). Describe the role of endothelial cells in hemostasis. What is the difference between hemostasis and blood coagulation? Compare the white and the red thrombus. What is the normal value of thrombocyte count? Describe the most important morphological features of the thrombocytes, size and types of granules. Explain the adhesion, aggregation and activation of thrombocytes. Enlist the factors that activate thrombocytes and their origin (site of production). What is the role of the endothelial cells in the regulation of hemostasis? Bleeding time. Normal values: thrombocyte count: /µL, bleeding time (Ivy's method): 3-5 min 22. Secondary hemostasis: blood clotting (coagulation). Inhibition of clotting (in vitro and in vivo). Fibrinolysis. Define the coagulation factors, their nomenclature, site of synthesis, and the mechanism of their action. Describe the extrinsic and intrinsic pathways of coagulation Expound the common phase of blood coagulation (convergence of extrinsic and intrinsic pathways) and the formation of the stable fibrin mesh. Explain the role of vitamin K in the synthesis of the so-called vitamin K-dependent coagulation factors. What is the "placenta sanguis"? Define the process of clot retraction, define the term serum and compare its composition with the blood plasma. Compare prothrombin time and coagulation time. Define INR, its calculation and significance. Expound the activation and regulation of the plasmin system. Describe the following systems and their regulation: thrombomodulin/protein C/protein S; heparin/antithrombin. Enlist substances that can be used to inhibit blood coagulation in vitro (EDTA, citrate) and define their mechanism of action. Enlist substances and drugs that can be used in vivo to inhibit thrombocyte activation and blood coagulation or to facilitate fibrinolysis (inhibitors of cyclooxygenase, heparin, vitamin K antagonists and plasminogen activators). Normal values: prothrombin time: s, INR: , coagulation time (Lee-White method): 5-8 min, fibrinogen: 3 g/l 1

2 Three steps occur in a rapid sequence: 3. Blood clotting 1. Vascular spasm (30 s) as the blood vessels constrict. Triggered by: a direct injury to vascular smooth muscle, chemicals released by endothelial cells and platelets (serotonin, TXA2, adrenalin) Thrombocyte reflexes initiated by local pain receptors thrombin Thrombocyte-derived 2. platelet plug formation (3-7 surface min), to form a temporary clotting seal factors cover the break in the vessel wall (primary hemostasis) 2. Thrombocyte adhesion, adhere to damaged endothelium, activation and aggreation platelet plug activation and aggregation 3. coagulation or blood clotting (5-10 min), reinforces the platelet plug with fibrin threads that act as Vasoactive a molecular glue substances (secondary hemostasis) conversion of the plug into definitive clot by fibrin 1. Vasoconstriction injury Time minutes hours 1. Vascular spasm Temporary vasoconstriction(minutes) Slows down circulation locally Mechanisms: Vasomotor neves Local metabolites (TXA2, serotonine, epinephrine) Pain-induced reflexes Passive compression 2

3 Platelets (thrombocyte) Thrombopoietin liver, kidney /µl blood(thrombocytopenia) Fragments of megakaryocytes cytoplasm Store: spleen µm, discoid shape 5-8 day without nucleus It has: Glycoproteins on its surface Tubular system big surface Contractile elements Mitochondria Glycogen Dens tubules (ER calcium store) Granules(dens, alpha) lysosome 2. Platelet plug formation a) Platelet adherence b) Platelet activation c) Platelet aggregation 3

4 2.a) Platelet adherence Adherence to the damaged vessel wall requires the expression of a protein called von Willebrandfactor (vwf) on the endothelial cell. Direct binding: GPIa-IIa Indirect binding GP Ib-IXcomplex + vwf 4

5 II.b) Platelet activation Activated platelet ACTIVATOR collagen TXA2 Serotonine SOURCE subendothelium Activated platelet Activated platelet Exposure to subendothelial collagen Adenylylcyclase Endothelial cell Adrenaline(α2) ADP Thrombin Activated platelet Activated platelet Bloodclotting cascade Cytosceletal activation Shape conversion GP IIb-IIIa exposition TXA 2 Guanylylcyclase FonyóAttila: Az orvosi élettan tankönyve (2011) PLC activation IP 3 + DAG Denzgranulum: Ca 2+ release Exocytosis PLA 2 activation MLCK enzyme activation citoskeletal rearrenegement 5

6 II.c) Platelet aggregation Activated platelets form pseudopodsontheir surface tobetter clumpand interact with one another GP IIb-IIIa complex activation Platelets clump together via fibrinogen and vwf as connecting agents Platelet actin and myosin filaments start contracting to solidify the plug Pathways of platelet aggregation.world J Cardiol September 26; 2(9):

7 Bleeding time: 4-6 min Ivy-method Platelet function blood tests Blood pressure cuff is inflated on the upper arm A standard incision (1x10mm) is made onthevolar surface of the lower arm The blooddropsare soaked upevery 30 s withfilter paper Prolonged bleeding time Deficiency or decreased number of thrombocytes (THROMBOCYTOPENIA) Impaired blood vessels ocytopenia-global-clinical-trials-review-h1-2015/ Antithrombotics Inhibitors of platelet aggregation a) Substances that increase camp level PGI 2 iloprost PDE inhibitors dipiridamol b) Chelating agents (in vitro) c) Aspirin (COX inhibitor) d) ADP-receptor antagonists ticlopidin, clopidogrel e) GP IIb/IIIa receptor antagonists tirofiban, eptifibatid 7

8 Aspirin also has an antiplatelet effect by inhibiting the production of thromboxane Today, aspirin is one of the most widely used medications in the world, with an estimated 40,000 tonnes of it being consumed each year.in countries where Aspirin is a registered trademark owned by Bayer, the generic term is acetylsalicylic acid (ASA). corticosteroids NSAIDs Second stage of hemostasis 3. Blood coagulation Reinforces the platelet plug by forming fibrin mesh Cascade of enzymatic reactions Requires clotting factors 8

9 Clotting factors Factor I II III IV V VII VIII IX X XI XII XIII Name Fibrinogen Prothrombin Thromboplastin(tissue factor) Calcium Proaccelerin Proconvertin Antihemophilic factor A Antihemophilic (Christmas) factor B Stuart-Prower-factor Antihemophilic factor C Hageman-factor Fibrinstabilizing(Laki-Lóránd) factor /1948/ Prekallikrein HMWK high molecular weight kininogen tissue factor (III) Anticoagulants: Antithrombin III Protein C Protein S Protein synthesis: liver Serine proteases, and transglutaminase (F XIII) Vitamin K-dependent factors FactorII, VII, IX and X Anticoagulants: Protein C and Protein S Vitamin K = cofactor fortheenzyme that catalyzes the conversion of glutamic acid residues to gamma-carboxyglutaminic acid residues itgives the possibility tobindwith calcium 9

10 Vitamin-K Forms: Vitamin K1 (fillokinon) green leafy vegetables Vitamin K2 (menakinon) bacteria Solubility: lipidsoluble Absorption: 10-70% of the intake Normal flora of bacteria and mixed nitrition is sufficient. Advised daily dose: 50-65µg. Hypovitaminosis excessive bleeding adulthood: after long-lasting antibiotic treatment, decreased Vitamin K intake childhood: small flora of bacteria sources:brocoli, cabbage lettuce, cabbage, spinach, milk products, honey, pollen, royal jelly, liver 2. Secunder haemostasis blood clotting clot: fibrin mesh + trapped blood cells Coagulating factors enzymes Clotting cascade(positive feedback) Anticoagulating processes Fibrinolysis 10

11 Contact activation in vitro blood clotting pathway No external factor is required Delay Amplification Tissue factor is required in vivo blood clotting pathway Extrinsic tenase Procoagulant effects Conversion of fibrinogen to fibrin Conversionof F XIII tof XIIIa fibrin stabilizing Conversionof F XI tof XIa intrinsic pathway Activates regulating proteins (F V and F VIII) Activation of platelets, endothelial cells and leukocytes Anticoagulant effects Protein C activation via thrombomodulin F Vaand F VIIIainactivation Antifibrinolytic effect Roles of thrombin 11

12 Anticlotting mechanisms Antithrombin III: (cofactor: heparin, heparane-sulphate) Inactivationof thrombin, F IXa, F Xa, FXIaand XIIa Protein C: (cofaktor: thrombomodulin) Thrombomodulin + thrombin + Protein C: enzymatic degradation of FVa and FVIIIa Increase the formation of plasmin Protein S: Protein C cofactor in the inactivation of FVa and FVIIIa Fibrin mesh formation Fibrinogen: is a soluble plasma glycoprotein, synthesized by the liver, that is converted by thrombin into fibrin during blood coagulation. Fibrinis then cross linked by factor XIII to form a clot. F XIIIa stabilizes fibrin 12

13 Fibrinolysis: enzymatic cleavage of the fibrin mesh Clotting time: Lee-White method, 7-10 min Venous blood, waterbath, tipping the tube back and forth every 30s, till blood does not flow out of the tube titled horizontally Prothrombin (PT, PTI, Quick) time: s (80-120%) Extrinsic + common pathway Reagent: FXa, FVa, PL, Calcium, tissue factor Firstfibrin fiberappearsatthetip of theneedle INR (International Normalized Ration): 0,8-1,2 (a)pti(activated parcial thromboplastin time): s Intrinsic + common pathway Reagent: FXa, FVa, PL, Calcium Thrombin(TI) time: s Fibrin production, antifibrinolytic treatment Plasma with anticoagulant Thrombin PTI Examination of blood clotting (a)ppti TI 13

14 Inhibitors of platelet aggregation a) Substances that increase camp level PGI2 iloprost PDE inhibitors dipiridamol b) Chelating agents(in vitro) c) Aspirin(COX inhibitor) d) ADP-receptor antagonists ticlopidin, clopidogrel e) GP IIb/IIIareceptor antagonists tirofiban, eptifibatid Anticoagulants a) Coumarin-derivatives (acenokumarol, warfarin) b) Heparin(UFH, LMWH) c) Hirudin 14

15 Anticoagulants invivo and invitro usage UnfractionatedHeparin(UFH) facilitatestheactionof antithrombin III LMWH: more predictable effect, longer half-life, less adverse effects Coumarin derivatives: dicumarol, warfarin Vitamin K antagonists Hirudin In vitro calcium removal from the blood(oxalates, chelating agents- citrate, EDTA); heparin Coumarin derivatives Acenocoumarol, warfarin prevents y-carboxylation of F II, VII, IX, X; Protein C and S Analytical Biochemistry421(2), 2012 Galium odoratum 15

16 Hirudin is a naturally occurring peptide in the salivary glands of medicinal leeches (such as Hirudo medicinalis) Thrombin antagonist Inhibits platelet aggregation, anticoagulating property(direct thrombin inhibitor), thrombolytic properties To treat haematomas and varicose veins 16