Factor XI plasma thromboplastin

Figure 5.3. Intrinsic and extrinsic blood clotting cascades. Factor I, fibrinogen Factor II, prothrombin (vitamin K-dependent) Factor III, thromboplastin Factor V, proac-celerin Factor VII, proconvertin (vitamin K-dependent) Factor VIII, antihemophilic factor Factor IX, Christmas factor (vitamin K-dependent) Factor X, Stnart factor (vitamin K-dependent) Factor XI, plasma thromboplastin Factor XII, Hageman factor Factor XIII, fibrin-stabilizing factor and Factor XIV, protein C (vitamin K-dependent). What was at one time called Factor IV is calcinm no factor has been assigned nnmber VI.

Tissue factor/thromboplastin xi Plasma thromboplastin antecedent (PTA) 3.4.27.27... 

Hageman factor (XII), antihemophilic globulin (VIII), Christmas factor (IX), plasma thromboplastin antecedent (XI), calcium (IV), and platelet phospholipids... 

Hageman Factor (Factor XII) and Plasma Thromboplastin Antecedent (Factor XI), /. Lab. Clin. Med. (1972) 80, 704. 

L12. Lindquist, P. A., Fujikawa, K., and Davie, E. W., Activation of bovine Factor IX (Christmas Factor) by Factor XI. (activated plasma thromboplastin antecedent) and a protease from Russell s viper venon. J. Biol. Chem. 253, 1902-1909 (1978). 

When blood is lost or clotting is initiated in some other way, a complex cascade of biochemical reactions is set in motion, which ends in the formation of a network or clot of insoluble protein threads enmeshing the blood cells. These threads are produced by the polymerisation of the molecules of fibrinogen (a soluble protein present in the plasma) into threads of insoluble fibrin. The penultimate step in the chain of reactions requires the presence of an enzyme, thrombin, which is produced from its precursor prothrombin, already present in the plasma. This is initiated by factor lit (tissue thromboplastin), and subsequently involves various factors including activated factor Vn, DC, X, XI and XII, and is inhibited by antithrombin in. Platelets are also involved in the coagulation process. Fibrinolysis is the mechanism of dissolution of fibrin clots, which can be promoted with thrombolytics. For further information on platelet aggregation and clot dissolution, see Antiplatelet drugs and thrombolytics , (p.697). 

The activated partial thromboplastin time (aPTT) measures the activity of the intrinsic system and common pathway (factors II, V, X, VIII, IX, XI, XII, high-molecular-weight kininogen, prekallikrein, and fibrinogen). aPTT reflects the time required for a flbrin clot to form after a partial thromboplastin, calcium, and an activating agent are added to the patient s plasma. aPTT is widely used for monitoring heparin therapy. 

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