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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 it to polymerize .
Fibrinogen is made and secreted into the blood primarily by liver hepatocyte cells. Endothelium cells are also reported to make small amounts of fibrinogen, but this fibrinogen has not been fully characterized; blood platelets and their precursors, bone marrow megakaryocytes, while once thought to make fibrinogen, are now known to take up and store but not make the glycoprotein.
Factor XIII, or fibrin stabilizing factor, is a plasma protein and zymogen. It is activated by thrombin to factor XIIIa which crosslinks fibrin in coagulation. Deficiency of XIII worsens clot stability and increases bleeding tendency. [1] Human XIII is a heterotetramer. It consists of 2 enzymatic A peptides and 2 non-enzymatic B peptides.
In the conversion of fibrinogen into fibrin, thrombin catalyzes the cleavage of fibrinopeptides A and B from the respective Aα and Bβ chains of fibrinogen to form fibrin monomers. [13] Factor XIIIa is a transglutaminase that catalyzes the formation of covalent bonds between lysine and glutamine residues in fibrin. The covalent bonds increase ...
Tissue factor, also called platelet tissue factor or Coagulation factor III, [5] is a protein present in subendothelial tissue and leukocytes which plays a major role in coagulation and, in humans, is encoded by F3 gene. Its role in the blood clotting is the initiation of thrombin formation from the zymogen prothrombin.
Following vascular injury, fibrinogen is cleaved by thrombin to form fibrin, which is the most abundant component of blood clots. In addition, various cleavage products of fibrinogen and fibrin regulate cell adhesion and spreading, display vasoconstrictor and chemotactic activities, and are mitogens for several cell types.
The formed elements are the two types of blood cell or corpuscle – the red blood cells, (erythrocytes) and white blood cells (leukocytes), and the cell fragments called platelets [12] that are involved in clotting. By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%.
Each molecule of Factor Xa can generate 1000 molecules of thrombin. This large burst of thrombin is responsible for fibrin polymerization to form a thrombus. Factor Xa also plays a role in other biological processes that are not directly related to coagulation, like wound healing, tissue remodelling, inflammation, angiogenesis and atherosclerosis.