He mostasis and Blood Coagulation

2. Hemostasis and Blood Coagulation

3. Thrombocytes • Cell fragments pinched off from megakaryocytes in red bone marrow • Important in preventing blood loss • Platelet plugs • Promoting formation and contraction of clots

4. Thrombocytes (Platelets) • Megakaryocytes fragment into small platelets either in the bone marrow or soon after entering the blood • Role of trombopoetin: it stimulates differentiation of megakaryocytes and formation of platelets (produced mainly in the liver, also in bone marrow) • Continuously being replaced. • Each platelet circulates for 9-12 days before being removed by splenic phagocytes. • Normal range is between150,000-300,000 platelets/mm3of blood. • A deficit of platelets is called thrombocytopenia

5. How are platelets formed? Flattened disk-like cell fragments : Platelets Megakaryocytes

8. Physical and Chemical Characteristics of Platelets • They have no nucleus, and therefore cannot reproduce 1- Actin, myosin and thrombosthenin (contractile proteins) 2- ER and golgi apparatus (Ca depot and synthesis of enzymes) 3- Mitochondria: ATP and ADP forming enzyme systems 4- Prostaglandin synthesis 5- Fibrin-stabilizing factor 6- Growth factor: Endothelial, vascular smooth muscle cells and fibroblasts

9. Cell Membrane of Platelets • A coat of glycoproteins that repulses adherence to normal endothelium • Membrane phospholipids that activate multiple stages in the blood-clotting process

10. Hemostasis Mechanisms • 1- Vascular Constriction (vasospasm) • 2- Formation of a platelet plug • 3- Formation of a blood clot as a result of blood coagulation • 4- Eventual growth of fibrous tissue into the blood clot (vascular repair) • Dissolution of clot (fibrinolysis)

11. Blood Vessel Damage Smooth muscle in BV wall contracts – VascularSpasm BV diameter  Blood loss slows 1- Vascular Constriction • Lasts about 30 mins • Release of a vasoconstrictor substance (thromboxane A2) by platelets • Endothelial cells at the injury site undergo changes and release • ADP • Prostaglandin • Other tissue factors • Endothelial cell membranes become sticky

12. 2- Formation of Platelet Plug (Platelet Phase) • ADHESION: Adherence of platelets to the injured vasvular endothelium; von Willebrand Factor (a protein) plays a role • AGGREGATION: Adherence of platelets to each other; ADP and serotonin (released by platelets) play roles

13. Thromboxane A2 (TXA2)  It is synthetized from membrane phospolipids in response to platelet adhesion  TXA2stimulates secretions and aggragation of platelets  In addition, it causes local vasoconstriction

14. Formation of platelet plug • Occurs within 15sec of the injury • Platelets begin to attach to sticky endothelial cells, the basement membrane, and to exposed collagen fibers. • As platelets “stick,” they become “activated.” Activated platelets release: • ADP  the primary stimulus for platelet aggregation (do you see positive feedback here?) • Thromboxane A2  causes platelet aggregation and local vasoconstriction • Serotonin  causes local vasoconstriction • Calcium ions • Aggregation of platelets eventually results in a platelet plug, a temporary mass of platelets that stops blood loss and forms a framework for the clot.

15.  Fibrinogen forms cross-bridges between platelets and thus contributes to formation of the platelet plug •  Actin and myosin of platelets contracts and the plug becomes stronger • Platelet plug occurs very rapidly and is considered to be primary plug of injured vessel •  Only this mechanism can be enough to close small damages

16. 3- Blood Coagulation in the ruptured vessel • Begins 30sec or more after severe vessel damage occurs (unlike the first 2 phases which begin almost immediately) • in 1 to 2 min if the trauma has been minor • 20 mins to an hour, the clot retracts (this closes the vessel further)

19. Fibrous organisation or dissolution of the blood clot • Once a blood clot has been formed, it can follow one of two courses: 1) It can become invaded by fibroblasts (which subsequently form connective tissue all through the clot) • role of growth factors secreted by platelets • organisation of the clot into fibrous tissue within 1-2 weeks 2) Dissolution of clot by enzymes (plasmin) released by the clot

20. Leaning Equlibrium Procoagulants Anticoagulants

21. Mechanism of Blood Coagulation • Formation of prothrombin activator • Conversion of prothrombin to thrombin • Formation of fibrin fibers

22. Conversion of Prothrombin to Thrombin • Prothrombin activator (PA) converts prothrombin to thrombin in presence of sufficient Ca2+ • Thrombin causes polymerization of fibrinogen to fibrin fibres within another 10-15 seconds • The rate-limiting factor in blood coagulation is formation of PA • Platelets also play a role in conversion of prothrombin to thrombin • Prothrombin: a plasma protein (alfa2 globulin) • It is continually formed in the liver • Vit K is required for normal formation of prothrombin

23. Conversion of Fibrinogen to Fibrin • Fibrinogen: Plasma protein • Action of thrombin on fibrinogen to form fibrin • Blood clot • Clot Retraction - Serum • Platelets are necessary for clot reaction to occur • They release fibrin-stabilizing factor • Contractionof actin, myosin and thrombosthenin is activated • As the clot retracts, the edges of broken blood vessel are pulled together

24. Formation of Prothrombin Activator:Initiation of Coagulation • 1) trauma to the vascular wall and adjacent tissues • 2) trauma to the blood • 3) contact of blood with damaged endothelial cells • Each of this leads to formation of PA • PA is generally considered to be formed in two ways: • Extrinsic pathway • Intrinsic pathway • Blood-clotting factors:

25. Blood-Clotting Factors • FI: Fibrinogen • FII*: Prothrombin • FIII: Tissue thromboplastin • FIV: Calcium (Ca+2) • FV: Proaccelerin (labile factor) • FVII*: Proconvertin (stabilizing factor) • FVIII: Antihemophilic Factor A (antihemophilic globulin) • FIX*: Antihemophilic Factor B (Christmas Factor) • FX*: Stuart Factor (Stuart-Prower Factor) • FXI: Antihemophilic Factor C (Plasma Thromboplastin) • FXII: Hageman Factor (touch-friction factor) • FXIII: Fibrin Stabilizing Factor (Laki-Lorand Factor) • *Factors that require Vit K • ►There is no Factor VI

26. Extrinsic Pathway for Initiating Coagulation 1- Release of tissue factor (Factor III) 2- Activation of Factor X Role of Factor VII and tissue factor 3- Effect of activated Factor X (Xa) to form prothrombin activator Role of factor V

27. Extrinsic Pathway

28. Intrinsic Pathway for Initiating Clotting 1- Blood trauma causes Activation of Factor XII Release of platelet phospholipids 2- Activation of Factor XI (role of kininogen and prekallikrein) 3- Activation of Factor IX by activated Factor XI 4- Activation of Factor X (Role of factor VIII) 5- Action of activated factor X to form PA 6- …

29. Intrinsic Pathway

30. Role of Calcium Ions • Except for the first two steps in intrinsic pathway, Ca2+ is required for all steps of blood clotting reactions • Therefore, in the absence of Ca2+, blood clotting by either pathway does not occur • Clotting can be prevented by precipitating of Ca2+ with substances like citrate or oxalate ions

31. İki mekanizmanın karşılaştırılması • Ekstrensek yolun patlayıcı doğası • 15 sn gibi kısa sürede oluşabilir • İntrensek yol ise daha yavaş gelişir (1-6 dk)

32. Prevention of Blood ClottingIntravascular Anticoagulants 1- Endothelial surface factors 2- Antithrombin action of fibrin and Antithrombin III 3- Heparin

33. Prevention of Blood ClottingIntravascular Anticoagulants 1- Endothelial surface factors a) Smoothness of the endothelial cell surface b) Layer of glycocalyx c) A protein bound with endothelium (thrombomodulin) binds thrombin - In addition, thrombomodulin activates protein C - Protein C acts as an anticoagulant by inactivating activated factors V and VIII

34. Prevention of Blood ClottingIntravascular Anticoagulants

35. Prevention of Blood ClottingIntravascular Anticoagulants 2- Antithrombin action of fibrin and Antithrombin III a) Fibrin fibers that themselves are formed during the process of clotting (85-90% of thrombin is adsorbed to the fibrin fibers) b) Antithrombin III (antithrombin-heparin cofactor) can bind thrombin. Thus, antithrombin III prevents conversion of fibrinogen to fibrin by inactivating thrombin

36. Prevention of Blood ClottingIntravascular Anticoagulants 3- Heparin - Produced largely by Mast cells and some basophils - Mast cells are abundant in tissue surrounding the capillaries of the lungs and to a lesser extent capillaries of the liver - The complex of heparin and Antithrombin III removes several other activated coagulation factors in addition to thrombin - Antithrombin-heparin cofactor removes factor IX, X, XI and XII

37. Lysis of Blood Clots - Plasmin • Plazminogen (profibrinolysin) – plasmin (fibrinolysin) • Plasmin is a proteolytic enzyme that resembles to pancreatic trypsin • The injured tissues and vascular endothelium very slowly release a powerful activator called tissue plasminogen activator (t-PA) • After a few days (the clot has stopped the bleeding), it converts plasminogen to plasmin which in turn removes the remaining unnecessary blood clot • Many small vessels are reopened by this mechanism

38. Lysis of Blood Clots - Plasmin

39. Thrombolytic Pathway PLAZMINOGEN t-PA PLASMIN Fibrin Polymers

40. Conditions that cause excessive bleeding in human beings 1- Vit K deficiency 2- Hemophilia 3- Thrombocytopenia

41. Bleeding Related with Vit K Deficiency Vit K deficiency and decrease in Prothrombin, factor VII, faktor IX ve factor X Most of the blood clotting factors are produced in the liver Liver diseases such as Hepatitis, cirrhosis and acute yellow atrophy Vit K is continually synthesized in the intestinal tract by bacteria So Vit K deficiency seldom occurs in adults – seen in new born Vit K is fat-soluble and absorbed into the blood along with the fats Obstruction of bile ducts

42. Hemophilia Occurs almost exclusively in males. In 85% of cases, it is caused by an abnormality or deficiency of Factor VIII (Hemophilia A or classical Hemophilia) In the other 15% of hemophilia cases, bleeding tendency is caused by deficiency of Factor IX. Both of these factors are transmitted genetically by way of the female chromosome. Bleeding time lasts longer, coagulation takes days to occur Treatment: injection of purified Factor VIII

43. Hemophilia • Refers to several different hereditary bleeding disorders with similar signs/symptoms • Hemophilia A • Results from lack of Factor VIII. Most common type (83%) • X-linked • Hemophilia B • Less common. Due to deficiency of Factor IX • Also X-linked

44. Thrombocytopenia • Presence of very low number of platelets in blood • People with thrombocytopenia have a tendency to bleed • Unless platelet count drops below 50,000/mm3, clinical signs (bleeding) do not appear • Platelet count of 50,000/mm3 is usually lethal • Causes: • Congenital: neonatal rubella, maternal use of tiazids • Adaptive: aplastic anemia, malnutrition, viral infections

45. Idiopatic Thrombocytopenic Purpura • Platalets are destroyed by own antibodies • Causes • Viral infections such as Rubella • Immune deficiency (such as chronic HIV)

46. Thrombus and Emboli • Trombus:An abnormal clot that develops in a blood vessel • Thrombosis: Abnormally high amount of thrombus formation • Emboli:If the clot (thrombus) breaks off and begins to drift in the bloodstream, it is called an embolus. It can plug arteries or arterioles in the brain, kidney, lungs or elsewhere.

47. Trombusand Emboli Left: Normal artery Right: Same artery with a large thrombus (arrow)

48. Cause of Thromboembolic Conditions • Roughened endothelial surface of a vessel • Arteriosclerosis, infection or trauma • Blood often clots when it flows very slowly through the blood vessels

49. Disseminated intravascular coagulation Large amounts of tissue factors enters blood Example: Sepsis (septisemi)

50. Anticoagulants • Acetyl salicylic acid (aspirin) inhibits platelet aggregation •  Oral anticoagulants •  Heparin •  Plazminogen activators (t-PA) •  Proteolytic agents (e.g. Streptokinase converts plasminogen to plasmin)