BLOOD-CLOTTING-1_37819

BLOOD-CLOTTING-1_37819 - BLOOD CLOTTING: OVERVIEW Summary...

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BLOOD CLOTTING: OVERVIEW Summary of Events (following loss of vascular integrity): Vascular Constriction : limits flow of blood to area of injury Platelet Activation : Platelets are activated by thrombin; Aggregate at site of injury, bind to collagen and form loose platelet plug. Platelet activation releases ADP, serotonin, phospholipids, serotonin, lipoproteins.All important for coagulation cascade Formation of fibrin mesh (clot): Clot entraps platelet plug. Fibrin clot produced by either the intrinsic or extrinsic pathway of the cascade. Clot dissolution: Occurs following tissue repair. Requires conversion of plasminogen to plasmin.
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Figure 1. Overview of blood coagulation Vessel Injury Platelet Activation Tissue Factor Coagulation Cascade Platelet Aggregation Platelet Plug Thrombin Clot Vasocon- striction
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I. BLOOD COAGULATION Homeostasis of the circulation requires hemostasis , which is control of blood vessel integrity and prevention of blood loss through abnormal bleeding.Hemostasis can occur by a) vascular spasm; b) formation of a platelet plug at site of blood vessel injury (primary hemostasis); c) initiation of the blood coagulation cascade (secondary hemostasis) To initiate a rapid response to vascular damage while blood continues to flow, procoagulants must be localized at site of trauma and inactivated when distant from trauma, A large number of proteins involved in blood clotting circulate at low concentrations as proenzymes. When needed, they participate in an elaborate cascade of enzymatic reactions to bring about coagulation. The coagulation cascade involves platelets, endothelial cells and plasma proteins. The end result is the generation of thrombi n at site of vascular injury. Thrombin is a serine protease, structurally similar to trypsin.
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Serine Proteases • Contain serine in the active site • This serine (-OH) is converted to an acid (-O - ) by catalytic triad of His + -Asp - -Ser. • The -O - attacks the carbonyl (C=O) carbon of peptide bonds, catalyzing hydrolysis . • Specificity is determined by substrate residues N- or C-terminal to the scissile bond. • Found in clotting, digestion, and maintenance of blood pressure • Secreted as zymogens .
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II. BLOOD COAGULATION Blood coagulation may occur as a result of accident (clot formation) or because of vascular disease (thrombus formation). The variety of factors involved is shown in the following
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This note was uploaded on 01/23/2011 for the course BCHS 4361 taught by Professor Echberg during the Spring '09 term at University of Houston.

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BLOOD-CLOTTING-1_37819 - BLOOD CLOTTING: OVERVIEW Summary...

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