批發(fā)和零售貿(mào)易零售業(yè)(編輯修改稿)
2025-01-20 05:39 本頁面
【文章內(nèi)容簡介】 activation ? Anticoagulant factors The coagulation system consists of three pathways (intrinsic, extrinsic and mon) Procoagulant Factors Coagulation Systems cont. Enzymatic factors ? Circulate as nonactive zymogens must be activated to function ? Activated enzymatic factors are not consumed during clotting (except factors II and XIII) ? Partial deficiency results in partial loss of clotting ability ? Activated enzymatic factors inhibited by antithrombin III (plexed with heparin) and some alpha2glycoproteins ? Enzymatic factors: ? XI and XII (contact factors) ? II, VII, IX and X (vitamin Kdependent factors) ? XIII (clot stabilizing factor or fibrinstabilizing factor) Coagulation Systems cont. Nonenzymatic factors ? Originate from liver but associate with platelet membranes (also found in plasma) ? Normal clotting with partial deficiency。 almost total absence needed to affect hemostasis or clotting ? Clotting consumes these factors absent in serum ? No known natural inhibitors ? Considered reactive proteins increased during inflammatory and neoplastic processes (except factor III) ? Nonenzymatic factors: ? Fibrinogen (factor I) ? Factor V ? Factor VIII:C (associated with Von Willebrand’s factor) Coagulation Cascade Interactions Does this turkey have factor XII? Of course, he does But, his feathered panion does not Coagulation Systems cont. Clot stabilization ? Fibrin stabilizing factor (factor XIII) forms fibrin strand crosslinks. ? Synthesized by monocytes and hepatocytes. ? Zymogen is activated by thrombin (plus calcium). ? A very small amount of factor XIII (2 10%) is adequate for hemostasis. ? Converts soluble fibrin monomers (unstable) to a fibrin polymer (stable). ? Lead, silver, zinc and snake venoms are known inhibitors. Coagulation Inhibitors The activity of coagulation system must be attenuated. ? Numerous inhibitors are found in blood. Coagulation is controlled by three types of actions. ? Inhibition of converting enzymes (., AT III, C1 esterase inhibitor, a2macroglobulin, a2antiplasmin, a1antitrypsin, HCII). ? Act on one or more of the converting enzymes (activated factors). ? AT IIIheparin pathway: major system 80% of the thrombin inhibitory action in plasma. ? Destruction of protein cofactors (., TMPCPS system). ? TMPCPS system degrades cofactors V VIII:C, inhibiting prothrombinase and tenase plexes, respectively. ? Blocking receptor availability needed for plex formation (., Tissue factor pathway inhibitor (TFPI) and annexin V). Proposed Mechanism of AT IIIHeparin System Heparin Thrombin Antithrombin III Lysine sites Serine site Arginine site H Th H AT III AT III Th Proposed Mechanism of Thrombomodulin, Protein C and Protein S (TMPCPS) System Thrombin Prothrombin Protein C Thrombomodulin Thrombin FXa Activated platelet PS FVa x Ca++ Ca++ Activated Protein C Proposed Mechanism of Tissue Factor Pathway Inhibitor (TFPI) Activity FXa Endothelium Tiss
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