![]() ![]() The K1/2 were not significantly changed after maturation, whereas rates of Xa formation at saturation with factor VII were increased. The K1/2 of human factor VII (concentrations giving half maximal rates of factor X activation) for the interaction with human and rabbit alveolar macrophage TF were 0.191 +/- 0.096 and 1.7 +/- 0.7 etamol/L, respectively. The km' did not change during macrophage maturation in culture, but V'max (apparent Vmax) was consistently increased. The km' (apparent km) of TF-factor VII enzymatic complexes assembled on alveolar macrophages for factor X were (258 +/- 55 and 475 +/- 264 nmol/L for human and rabbit cells, respectively). After macrophage maturation in culture for 20 hours with LPS (endotoxin) added, the factor X activation rate was increased two- to sixfold. At plasma concentrations of the purified factors, factor Xa was formed on freshly isolated macrophages at approximately 5.4 pmol/min/10(6) cells. Detection of rapid factor Xa formation on macrophages required addition of exogenous factors VII and X. We found rapid activation of factor X to Xa on alveolar macrophage surfaces. Kinetic parameters of the factor X activating reaction were determined by functional titrations of factors VII and X with macrophage tissue factor (TF) added. Vitamin K is an essential factor of the coagulation cascade.We examined assembly and expression of the factor X activating complex on human and rabbit alveolar macrophages.Thrombomodulin: released by the endothelium and converts thrombin into an inactive form.Prostacyclin (PGI2): released by the endothelium and inhibits platelet activation.Plasmin: generated by proteolytic cleavage of plasminogen, a potent fibrinolytic that degrades fibrin and destroys clots.Tissue factor pathway inhibitor (TFPI): limits the action of tissue factor (TF) and the factors it produces.Antithrombin: a serine protease inhibitor that degrades thrombin, Factor IXa, Factor Xa, Factor XIa, and Factor XIIa.Protein C: a vitamin K-dependent serine protease enzyme that degrades Factor V and factor VIII.Many anticoagulants prevent unnecessary coagulation, These mechanisms include: Tissue Factor is released when the vessel wall is ruptured. It requires Tissue Factor (tissue thromboplastin), a substance which is "extrinsic to", or not normally circulating in the vessel. The Extrinsic pathway is the other route to coagulation.The Intrinsic pathway requires only elements (clotting factors, Ca++, platelet surface etc.) found within, the vascular system. The Intrinsic pathway is initiated by events that take place within the lumen of blood vessels.Either of two distinct pathways can initiate coagulation.The liver manufactures the coagulation factors (proteins).They provide a surface upon which the chemical reactions of coagulation can take place. Phospholipids are prominent components of cellular and platelet membranes.Platelets in the clot begin to shrink, tightening the clot and drawing together the vessel walls to initiate the process of wound healing.Thrombin facilitates the conversion of a protein called fibrinogen to fibrin, forming an interlocking network of fibers and a framework for the clot.The reaction requires Ionized calcium ( Ca++ ) that is available in the blood and from intracellular sources.Platelets also release prothrombin activators that catalyze circulating prothrombin, into thrombin.The platelets degranulate and release ADP (adenosine diphosphate), serotonin, and thromboxane A2 which activating more platelets. If the platelet plug is not enough to stop the bleeding, the platelets secrete granules that stick to proteins in the vessel wall. The process requires coagulation factors, calcium, and phospholipids. The gel plugs leaks in blood vessels and stops the loss of blood. Untitled Document The Blood Coagulation Processīlood coagulation is the third stage of hemostasis that converts circulating substances within the blood into an insoluble gel. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |