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The division of coagulation in two pathways is arbitrary, originating from laboratory tests in which clotting times were measured either after the clotting was initiated by glass, the intrinsic pathway; or clotting was initiated by thromboplastin (a mix of tissue factor and phospholipids), the extrinsic pathway.
[4] [5] [6] The ability of FXII to bind to negatively charged surfaces and activate coagulation forms the basis of the aPTT test, in which artificial materials act as a surface for contact activation. This test is used to measure the contact activation pathway (intrinsic pathway) and the common pathway of clotting. [7]
Therefore, although the coagulation cascade can be triggered in vitro through the intrinsic pathway only, in vivo coagulation is triggered by the extrinsic pathway. However, the model better describing how coagulation works is the so-called cell-based model, a more integrated picture of the whole process, in which phospholipid surfaces, such as ...
Historically, thromboplastin was a lab reagent, usually derived from placental sources, used to assay prothrombin times (PT time). Thromboplastin, by itself, could activate the extrinsic coagulation pathway. When manipulated in the laboratory, a derivative could be created called partial thromboplastin, which was used to measure the intrinsic ...
Blood coagulation pathways in vivo showing the central role played by thrombin. Factor Xa is the activated form of the coagulation factor X, also known as thrombokinase. Factor X is an enzyme, a serine endopeptidase, which plays a key role at several stages of the coagulation system. Factor X is synthesized in the liver.
Factor XI (FXI) is produced by the liver and circulates as a homo-dimer in its inactive form. [9] The plasma half-life of FXI is approximately 52 hours. The zymogen factor is activated into factor XIa by factor XIIa (FXIIa), thrombin, and FXIa itself; due to its activation by FXIIa, FXI is a member of the "contact pathway" (which includes HMWK, prekallikrein, factor XII, factor XI, and factor IX).
The extrinsic pathway of apoptosis refers to cell death induced by external factors that activate the death-inducing signaling complex. The extrinsic pathway of blood coagulation is also known as the tissue factor pathway and refers to a cascade of enzymatic reactions resulting in blood clotting and is done with the addition of injured tissue ...
The intrinsic pathway of apoptosis (also known as the mitochondrial pathway, intracellular pathway, or intrinsic apoptosis), cell death initiated by changes in mitochondria. The intrinsic pathway of blood coagulation (also known as the contact activation pathway), a cascade of enzymatic reactions resulting in blood clotting.