Immunology
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Description
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. Secondary haemostasis then follows—plasma components called coagulation factors respond (in a complex cascade) to form fibrin strands which strengthen the platelet plug. 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. The activated platelets then release the contents of their granules, these contain a variety of substances that stimulate further platelet activation and enhance the haemostatic process.
The use of adsorbent chemicals, such as zeolite, and other haemostatic agents is also being explored for use in sealing severe injuries quickly. [1]
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Discussion
| Number and/or name | Function |
| I (fibrinogen) | Forms clot (fibrin) |
| II (prothrombin) | Its active form (IIa) activates I, V, VII, XIII, protein C, platelets |
| Tissue factor | Co-factor of VIIa (formerly known as factor III) |
| Calcium | Required for coagulation factors to bind to phospholipid (formerly known as factor IV) |
| V (proaccelerin, labile factor) | Co-factor of X with which it forms the prothrombinase complex |
| VI | Unassigned – old name of Factor Va |
| VII (stable factor) | Activates IX, X |
| VIII (antihemophilic factor) | Co-factor of IX with which it forms the tenase complex |
| IX (Christmas factor) | Activates X: forms tenase complex with factor VIII |
| X (Stuart-Prower factor) | Activates II: froms prothrombinase complex with factor V |
| XI (plasma thromboplastin antecedent) | Activates XII, IX and prekallikrein |
| XII (Hageman factor) | Activates prekallikrein and fibrinolysis |
| XIII (fibrin-stabilizing factor) | Crosslinks fibrin |
| von Willebrand factor | Binds to VIII, mediates platelet adhesion |
| Prekallikrein | Activates XII and prekallikrein; cleaves HMWK |
| High molecular weight kininogen (HMWK) | Supports reciprocal activation of XII, XI, and prekallikrein |
| Fibronectin | Mediates cell adhesion |
| Antithrombin III | Inhibits IIa, Xa, and other proteases |
| Heparin cofactor II | Inhibits IIa, cofactor for heparin and dermatan sulfate ("minor antithrombin") |
| Protein C | Inactivates Va and VIIIa |
| Protein S | Cofactor for activated protein C (APC, inactive when bound to C4b-binding protein) |
| Protein Z | Mediates thrombin adhesion to phospholipids and stimulates degradation of factor X by ZPI |
| Protein Z-related protease inhibitor (ZPI) | Degrades factors X (in presence of protein Z) and XI (independently) |
| Plasminogen | Converts to plasmin, lyses fibrin and other proteins |
| Alpha 2-antiplasmin | Inhibits plasmin |
| Tissue plasminogen activator (tPA) | Activates plasminogen |
| Urokinase | Activates plasminogen |
| Plasminogen activator inhibitor-1 (PAI1) | Inactivates tPA & urokinase (endothelial PAI) |
| Plasminogen activator inhibitor-2 (PAI2) | Inactivates tPA & urokinase (placental PAI) |
| Cancer procoagulant | Pathological factor X activator linked to thrombosis in cancer |
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