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Fibrin (also called Factor Ia) is a fibrous, non-globular protein involved in the clotting of blood. It is formed by the action of the protease thrombin on fibrinogen which causes the latter to polymerize. The polymerized fibrin together with platelets forms a hemostatic plug or clot over a wound site. When the lining of a blood vessel is broken, platelets are attracted forming a platelet plug. These platelets express thrombin receptors on their surfaces that bind serum thrombin molecules which in turn convert soluble fibrinogen in the serum into fibrin at the wound site. Fibrin forms long strands of tough insoluble protein that are laid down and are bound to the platelets. Factor XIII completes the cross-linking of fibrin so that it hardens and contracts. The cross-linked fibrin forms a mesh overlying the platelet plug that completes the clot. == Role in disease == Excessive generation of fibrin due to activation of the coagulation cascade leads to thrombosis, the block of a vessel by an agglutination of red blood cells, platelets, polymerized fibrin and other components. Ineffective generation or premature lysis of fibrin predisposes to hemorrhage. Dysfunction or disease of the liver can lead to a decrease in the production of fibrin's inactive precursor, fibrinogen, or to the production of abnormal fibrinogen molecules with reduced activity (dysfibrinogenaemia). Hereditary abnormalities of fibrinogen (the gene is carried on chromosome 4) are of both quantitative and qualitative in nature and include afibrinogenaemia, hypofibrinogenaemia, dysfibrinogenaemia, and hypodysfibrinogenaemia. Consequences of reduced, absent, or dysfunctional fibrin is likely to render patients as hemophiliacs. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fibrin」の詳細全文を読む スポンサード リンク
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