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Independently activating factor X
- The extrinsic and intrinsic coagulation pathways both lead into the final common pathway by independently activating factor X. The extrinsic pathway involves initiation by factor III (i.e., tissue factor) and its interaction with factor VII. Whereas, factors XII, XI, IX, and VIII are utilized in the intrinsic pathway.
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Nov 8, 2021 · What are the three pathways of coagulation? Coagulation consists of three pathways, the extrinsic, intrinsic, and common pathways, that interact together to form a stable blood clot. The extrinsic and intrinsic coagulation pathways both lead into the final common pathway by independently activating factor X.
- Introduction
- The Extrinsic Pathway
- The Common Pathway
- The Intrinsic Pathway
- Regulating The Coagulation Cascade
- Coagulation Screening
- Dysfunction of The Coagulation Cascade
- Key Points
- References
The coagulation cascade is a series of reactions, catalysed by protein enzymes known as coagulation ‘factors’. When activated, these factors trigger the conversion of other factors in the coagulation cascade resulting in secondary haemostasis. Secondary haemostasis refers to the stabilisation of activated platelets due to the actions of strands of ...
Initiation of the coagulation cascade is usually mediated by tissue factor via the extrinsic pathway. Tissue factor is expressed on the surface of many cells found outside blood vessels but not on the surface of circulating blood cells or the endothelium. When the endothelium is damaged, tissue factor comes into contact with blood and combines with...
The common pathway begins with activation of factor X (to factor Xa) via either the extrinsic pathway or the intrinsic pathway. It is the final stage of the coagulation cascade and leads to the formation of thrombin and fibrin. Factor Xa combines with factor V, platelet membrane phospholipids and Ca2+ ions to convert prothrombin into thrombin. Thro...
The intrinsic pathway can be activated by surface contact, when damage to the vascular endothelium leads to exposure of clotting factors to negatively charged subendothelial surfaces, mediated by the molecule Kallikrein. Within blood vessels, thrombin generated from previous activation of the extrinsic pathway also activates the intrinsic pathway. ...
Without regulatory mechanisms, the positive feedback looptriggered by thrombin in the intrinsic pathway would continue indefinitely and cause dangerous levels of clotting in the blood. For this reason, various proteinsinhibit aspects of the coagulation cascadeonce enough thrombin has been produced. Protein C is produced in response to thrombin bind...
Multiple tests exist to assess haemostasis. They involve adding triggers to a sample of reversibly anticoagulated plasma (by citrate) and measuring the time taken for fibrin to form. The two most frequently performed tests are the prothrombin time (PT) and the activated partial thromboplastin time(APTT). For more information on interpreting these t...
Dysfunction of the coagulation cascade can be caused by several medical conditions: 1. Haemophiliais a congenital deficiency in either factor VIII (haemophilia A), factor IX (haemophilia B) or factor XI (haemophilia C) leading to defective clotting and therefore a tendency to bleed. 2. Chronic liver disease can lead to defective coagulation as many...
The coagulation cascade is one of the key components in the cessation of bleeding (haemostasis), by generating afibrin meshthat stabilises activated plateletsTwo pathways (the extrinsic and intrinsic) both result in the activation of factor X, which leads to the conversion of prothrombin into thrombinThrombin converts fibrinogen into fibrinand triggers the activation of factor XIII to cross-link the fibrin strands and stabilise the clotA stable clotis formed by activated platelets, fibrin and factor XIIIaHoffbrand A. V., Moss P. A. H., 2011., Essential Haematology, 6thEdition, John Wiley & Sons, New YorkRalston S. H., et al., 2018., Davidsons Principles and Practice of Medicine, 23rdEdition, Elsevier, EdinburghNaish J., Syndercombe Court D., 2019., Medical Sciences, 3rdEdition, Elsevier, EdinburghHall J. E., Hall M. E., 2021., Guyton and Hall Textbook of Medical Physiology, 14thEdition, Elsevier, Edinburgh- Ewan Evans
The extrinsic pathway, which normally is triggered by trauma. The intrinsic pathway, which begins in the bloodstream and is triggered by internal damage to the wall of the vessel. Both of these merge into a third pathway, referred to as the common pathway (see Figure 18.5.1 b ).
- Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Mat...
- 2019
The contact pathway of triggering blood clotting has also been termed the “intrinsic” pathway, since it can be triggered without adding a source of TF to the blood or plasma. This pathway is actually triggered when plasma comes into contact with certain types of artificial surfaces.
- Stephanie A. Smith, Richard J. Travers, James H. Morrissey
- 10.3109/10409238.2015.1050550
- 2015
- 2015
Learning Objectives. By the end of this section, you will be able to: Describe the three mechanisms involved in hemostasis. Explain how the extrinsic and intrinsic coagulation pathways lead to the common pathway, and the coagulation factors involved in each. Discuss disorders affecting hemostasis.
Jul 17, 2023 · This process occurs via two pathways which unite downstream to form the common pathway. These are: The extrinsic pathway: This is triggered by external trauma which causes blood to escape the circulation. The intrinsic pathway: This is triggered by internal damage to the vessel wall.
Differentiate among the intrinsic (contact activation), extrinsic (cell injury), and common pathways of the coagulation cascade. Explain how the positive feedback loops in the platelet and coagulation phases promote hemostasis. Explain the role of vitamin K in blood clotting.
