Lecture Master-1 - Introduction to Haemostasis

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Normal Hemostasis Normal Hemostasis By: By: Shahira El Shafie
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Learning Outcomes By the end of learning activities the Master  degree student will demonstrate an   understanding of the coagulation mechanism;  describe disease states associated with  abnormal coagulation values; and perform  basic laboratory coagulation analysis.  The  student will evaluate laboratory test  outcomes and correlate test results with  patient condition(s); and evaluate the  suitability of clinical specimens for  coagulation testing.
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Hemostasis is the process by which the body  spontaneously stops bleeding and maintains blood  in the fluid state within the vascular compartment. Four major systems are involved in the hemostatic  mechanism: 1.  Vascular system 2.  Platelet system 3.  Fibrin   forming (coagulation) system  (Coagulation Factors) 4.  Fibrinolytic system 
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Hemostasis: BV Injury Platelet Activation Plt-Fusion Blood Vessel Constriction Coagulation Activation Stable Hemostatic Plug Thromibn, Fibrin Reduced Blood flow Tissue Factor Primary hemostatic plug Neural
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I.  Vascular System Contraction of vessels (vasoconstriction)  and reflex stimulation of adjacent vessels.  Diversion of blood flow around damaged  vasculature.   Contact   activation of the coagulation  system and platelets
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  Platelet Plug Formation  1. Adhesion:  exposure to subendothelial  connective tissue, such as collagen fibers   initiates platelet adhesion.   2. Aggregation:  platelets begin to stick  together .
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Three stages of coagulation:  1.  Formation of plasma thromboplastin 2.  Conversion of prothrombin to thrombin 3.  Conversion of fibrinogen to fibrin
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Coagulation: Intrinsic 12,11,9,8 (aPTT-) Extrinsic-7 (PT) Prothrombin Thrombin Fibrinogen Fibrin Common Path (TT) FX FXa
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Clot formation & retraction Fibrinogen Fibrin Mononer Fibrin Polymer Cross Linked Fibrin Thrombin F-XIIIa
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Process-  primary  haemostasis In a normal individual, coagulation is  initiated within 20 seconds after an injury  occurs to the blood vessel damaging the  endothelial cells Platelets  immediately form a haemostatic  plug at the site of injury. This is called  primary  haemostasis
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Platelets Bone marrow – Megakaryocytes –  Life span 7-10d,  N.count – 150-400x10 /l
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The adhesion of circulating platelets to  subendothelial matrix components such as  collagen, fibronectin, and von Willebrand  factor, which are exposed after vessel  damage Adhesion to the damaged vessel wall  induces Platelet activation The  platelets undergo shape change, and  expose and activate fibrinogen receptors  (platelet glycoprotein IIb/IIIa). Exposure of 
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This note was uploaded on 04/24/2011 for the course CLINICAL P 101 taught by Professor Shahiraelshafie during the Spring '11 term at Cairo University.

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Lecture Master-1 - Introduction to Haemostasis

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