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Fibrinogen (coagulation factor I) is a glycoprotein complex, produced in the liver, [1] that circulates in the blood of all vertebrates. [2] During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood clot .
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 it to polymerize. The polymerized fibrin, together with platelets, forms a hemostatic plug or clot over a wound site.
The coagulation factors are generally enzymes called serine proteases, which act by cleaving downstream proteins. The exceptions are tissue factor, FV, FVIII, FXIII. [28] Tissue factor, FV and FVIII are glycoproteins, and Factor XIII is a transglutaminase. [27] The coagulation factors circulate as inactive zymogens. The coagulation cascade is ...
Thrombin (Factor IIa) (EC 3.4.21.5, fibrose, thrombase, thrombofort, topical, thrombin-C, tropostasin, activated blood-coagulation factor II, E thrombin, beta-thrombin, gamma-thrombin) is a serine protease, that converts fibrinogen into strands of insoluble fibrin, as well as catalyzing many other coagulation-related reactions.
The ELT measures fibrinolysis by clotting the euglobulin fraction (primarily the fibrinolytic factors fibrinogen, PAI-1, tPA, α 2-antiplasmin, and plasminogen) from plasma and then observing the time required for clot dissolution. A shortened lysis time indicates a hyperfibrinolytic state and bleeding risk.
Fibrinogen comprises 7% of blood proteins; conversion of fibrinogen to insoluble fibrin is essential for blood clotting. The remainder of the plasma proteins (1%) are regulatory proteins, such as enzymes, proenzymes, and hormones. All blood proteins are synthesized in liver except for the gamma globulins. [1]
The dysfibrinogenemias consist of three types of fibrinogen disorders in which a critical blood clotting factor, fibrinogen, circulates at normal levels but is dysfunctional. Congenital dysfibrinogenemia is an inherited disorder in which one of the parental genes produces an abnormal fibrinogen.
Thrombin is an enzyme that splits fibrinogen into fibrin monomers in 10 to 60 seconds, which aggregate to form a three-dimensional gel-like structure. Thrombin also activates factor XIII from the human body to factor XIIIa, which then cross-links the fibrin monomers to form a stable clot.