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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 clots function primarily to occlude blood vessels to stop bleeding ...
Fibrin is formed after thrombin cleavage of fibrinopeptide A (FPA) from fibrinogen Aalpha-chains, thus initiating fibrin polymerization. Double-stranded fibrils form through end-to-middle domain (D:E) associations, and concomitant lateral fibril associations and branching create a clot network.
Plasmin breaks down fibrin into soluble parts called fibrin degradation products (FDPs). FDPs compete with thrombin, and thus slow down clot formation by preventing the conversion of fibrinogen to fibrin. This effect can be seen in the thrombin clotting time (TCT) test, which is prolonged in a person that has active fibrinolysis.
Alexander Schmidt suggested that the conversion from fibrinogen to fibrin is the result of an enzymatic process, and labeled the hypothetical enzyme "thrombin" and its precursor "prothrombin". [ 59 ] [ 60 ] Arthus discovered in 1890 that calcium was essential in coagulation.
Fibrinogen beta chain, also known as FGB, is a gene found in humans and most other vertebrates with a similar system of blood coagulation. The protein encoded by this gene is the beta component of fibrinogen , a blood-borne glycoprotein composed of three pairs of nonidentical polypeptide chains.
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]
This process involves the conversion of fibrinogen, a soluble glycoprotein, into fibrin, an insoluble glycoprotein, using the enzyme thrombin. The fibrinogen forms fibrin to encase the platelet thrombus, thus creating a secondary hemostatic plug that is much more stable and securely attached to the vessel wall. [4]
This test is repeated with pooled plasma from normal patients. The difference in time between the test and the 'normal' indicates an abnormality in the conversion of fibrinogen (a soluble protein) to fibrin, an insoluble protein. [2] The thrombin time compares the rate of clot formation to that of a sample of normal pooled plasma.
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