Tabuk University Faculty of Applied Medical Sciences Department Of Medical Lab. Technology 3 rd Year – Level 5 – AY

Platelets, Blood coagulation and Haemostasis By/ Dr. Walid ZAMMITI; Phd M.Sc; MLT 2

OBJECTIVES  An overview of Haemostatic Mechanism, Platelet structure and function,  Define the term Haemostasis coagulation, fibrinolysis, and hemorrhage.  List the major and minor systems involved in maintaining hemostasis.  Describe the events that take place in primary hemostasis  Explain the role of platelets in the haemostatic process.  List steps in platelet plug formation  Name essential elements for the process of platelet adhesion.  Describe the process of platelet aggregation.  Describe the events take place in secondary hemostasis.  Name the product responsible for stabilization of the haemostatic plug.  List characteristics for the contact coagulation proteins.  List characteristics for the prothrombin proteins.  Interaction of the Fibrinolytic, Coagulation Systems and Related Pathology.  Name the component of the coagulation and fibrinolytic system. 3

Concept of Normal Haemostasis normal haemostatic response  The normal haemostatic response to vascular damage depends on interaction between the blood vessel wall, circulating platelets and blood coagulation factors.  Haemostasis : the arrest of bleeding by the physiological properties of vasoconstriction, platelets and coagulation factors. 4

Without this balance, the individual may experience either excessive bleeding (poor clot formation or excessive Fibrinolysis) Vaso-occlusion: uncontrolled formation of thrombin in vascular system, occluding vessels and depriving organs of blood. 5

Components of hemostasis 1. Blood vessels: --considered to be an anticoagulant surface, to prevent a clot from forming on their surface. 2. Platelets: --help maintain the integrity of the vessel lining, and they 'plug' any rupture in the circulatory vessels. 3. Plasma proteins (coagulation factors): --soluble circulating blood proteins function in the proper maintenance of hemostasis. 6

Platelets  It is formed by fragmentation of the cytoplasm of megakaryocytes.  Disc-shaped, non nucleated cells with complex internal structure. granules  3 major types of intracellular granules: 1.lysosomes 2.  -granules contain: *coagulation factors (fibrinogen, von Willebrand Factor, and coagulation factors V and VIII); and platelet-derived growth factor (PDGF). 3. dense granules contain: *ADP, ATP and serotonin.  - and dense granules contents released by platelet activation 7

Platelet Structure *Thrompopoeitin is the main regulator of platelet production *Life span 7-10 d, Normal count – x10 9 /l *1/3 of plts. are trapped in normal spleen (more than 90% in massive splenomegaly) *Functions: Hemostatic plug formation Some coagulation factors - release, synthesis Surface glycoproteins are important in platelet adhesion (vessel wall) and aggregation (platelet-platelet)  (GpIa, GPIb,GPIIbIIIa) 8

Process-primary haemostasis haemostasis 20 seconds  Normal coagulation is initiated within 20 seconds after the injury which damage the endothelial cells.endothelial cells adhere release aggregate  In order for hemostasis to occur, platelets must adhere to exposed collagen, release the contents of their granules, and aggregate. The adhesion of platelets to the collagen exposed on endothelial cell surfaces is mediated by von Willebrand factor (vWF). bridge  The function of vWF is to act as a bridge between a specific glycoprotein complex on the surface of platelets (GPIb-GPIX-GPV) and collagen fibrils 9

 When Platelets adhere, they become activated and change in shape to become spheres with pseudopodia.  Then they release their granules contents which induce aggregation (platelet to platelet), and further promote vasoconstriction. primary haemostasis.  This is called primary haemostasis. 10

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Secondary haemostasis coagulation factors fibrin  Secondary haemostasis then follows—plasma components called coagulation factors respond (in a complex cascade) to form fibrin strands which strengthen the platelet plug. fibrinplasmafibrin  Contrary to popular belief, coagulation from a cut on the skin is not initiated by air or drying out, but by platelets adhering to and activated by collagen in the blood vessel endothelium.collagenendothelium 13

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Coagulation cascade Fig. Contact Activation pathway  The coagulation cascade of secondary hemostasis has two pathways, the Contact Activation pathway (formerly known as the Intrinsic Pathway) Tissue Factor pathway  And the Tissue Factor pathway (formerly known as the Extrinsic pathway) that lead to fibrin formation.  The pathways are a series of reactions, in which enzymes of serine protease (except factor XIII) are activated to become active components that then catalyze the next reaction in the cascade. serine protease common pathway  The two pathways lead to the formation of a fibrin clot. Although they are initiated by distinct mechanisms, the two converge on a common pathway that leads to clot formation. 15

Coagulation: Intrinsic 12,11,9,8 (APTT) Extrinsic-7 (PT) Prothrombin  Thrombin Fibrinogen  Fibrin Common Path (TT) FX  FXa 16

 The intrinsic cascade (which has less in vivo significance in normal physiological circumstances than the extrinsic cascade) is initiated when contact is made between blood and exposed negatively charged surfaces.  The extrinsic pathway is initiated upon vascular injury which leads to exposure of tissue factor, TF (also identified as factor III), a subendothelial cell-surface glycoprotein that binds phospholipid. 17

FibrinogenFibrin Thrombin Prothrombin Xa Va 18

FibrinogenFibrin Thrombin Prothrombin Xa Va VIIa TF (Thromboplastin) Extrinsic Pathway 19

FibrinogenFibrin Thrombin Prothrombin Xa Va VIIa TF Extrinsic Pathway IXa VIIIa XIa XIIa Intrinsic pathway 20

FibrinogenFibrin Thrombin Prothrombin Xa VIIa TF Extrinsic Pathway IXa VIIIa Ca ++ XIa XIIa Intrinsic pathway XIIIa Soft clot Fibrin Hard clot Ca ++ phospholipid 21

 The coagulation factors are generally serine proteases: enzymes circulate as inactive zymogens (inactive enzyme precursor)serine proteasesenzymeszymogens  Contact factors  Contact factors : Prekallikrein (PK), High molecular weight kininogen (HMWK), Factor XII, Factor XI  Labile factors : Factor V, Factor VIII  Vitamine K dependent factors : Factors II, VII, IX and X, as well as Protein S, Protein C  Co-factors : Factor VIII, Factor V, Factor III (tissue factor), Ca ++ 22

Haemostatic response: Summary  Injury  Blood vessels : Vasoconstriction  Platelets : adhesion, release, change in shape, aggregation  Coagulation factors : formation of fibrin : stabilizes platelets aggregation.  Hard clot : factor XIIIa  Finally, the clot must be dissolved. (fibrinolysis) 23

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Regulators of Coagulation 1.Protein C system 1.Protein C system : physiological anticoagulant. With protein S, they degrades FVa and FVIIIa. Antithrombin 2. Antithrombin : degrades thrombin, FIXa, FXa, FXIa, and FXIIa. Tissue factor pathway inhibitor (TFPI) : 3. Tissue factor pathway inhibitor (TFPI) : limits the action of tissue factor (TF). 25

Fibrinolysis  In fibrinolysis, a fibrin clot, is broken down.fibrin Plasmin  The main component of fibrinolytic system is Plasmin which is produced in an inactive form, plasminogen, in the liver. plasminogen 26

Tests of Hemostasis:  Screeningtests  Screening tests: Bleeding Time - To test Platelet function(adhesion, aggregation) & vascular function. Clotting Time : tests plts count & function and coagulation. ProthrombinTime (PT): tests Extrinsic pathway. Activated Partial Thromboplastin Time (APTT): test Intrinsic pathway. Thrombin clotting Time (TCT): common pathway.  Specifictests  Specific tests: Factor assays Tests of thrombosis – TCT, FDPs Platelet function studies: Adhesion, Aggregation, Release tests. Blood film and bone Marrow examination. 27

Disorders of Hemostasis  Vascular disorders  Vascular disorders – Scurvy, easy bruising, Henoch-Schonlein purpura.  Platelet disorders Quantitative - Thrombocytopenia Qualitative - Platelet function disorders – Glanzmans  Coagulation disorders Congenital - Haemophilia (A, B), Von-Willebrands Acquired - Vitamin-K deficiency, Liver disease

Thank you 29