Extrinsic
Blood coagulation can occur either through an intrinsic or extrinsic pathway. The first step in either pathway begins with the production of Factor X,which marks the common pathway of coagulation.
extrinsic pathway of coagulation the mechanism that produces fibrin following tissue injury, beginning with formation of an activated complex between tissue factor and factor VII and leading to activation of factor X, inducing the reactions of the common pathway of coagulation.intrinsic pathway of coagulation a sequence of reactions leading to fibrin formation, beginning with the contact activation of factor XII, and resulting in the activation of factor X to initiate the common pathway of coagulation.
The extrinsic coagulation system is one of the two initial pathways in the blood coagulation process that is activated by external trauma or injury. It involves factors released from damaged blood vessels and tissues to initiate clot formation. This pathway ultimately converges with the intrinsic pathway to form a stable blood clot.
The extrinsic pathway shortcut allows for a rapid response to tissue injury by activating factor X directly, leading to a quicker initiation of the coagulation cascade. The multiple steps of the intrinsic pathway provide amplification of the coagulation response, resulting in a more robust clot formation and greater sensitivity to stimuli.
The prothrombin time (PT) test measures how long it takes for blood to clot. This test evaluates the coagulation factors involved in the extrinsic pathway.
The intrinsic pathway of blood coagulation is initiated within the bloodstream by damage to the blood vessel, while the extrinsic pathway is initiated outside the bloodstream by tissue factor released from damaged tissues. Both pathways ultimately converge to activate factor X and lead to the formation of a blood clot.
An important difference between the extrinsic and intrinsic blood clotting pathways is the way they are initiated. The extrinsic pathway is activated by external trauma that exposes tissue factor, while the intrinsic pathway is triggered by factors within the bloodstream, such as collagen or platelets. Additionally, the extrinsic pathway is faster and primarily involved in the initial response to injury, while the intrinsic pathway is more complex and amplifies the clotting process.
The coagulation cascade is classically divided into three pathways. The tissue factor (formerly known as the extrinsic) and the contact activation (formerly known as the intrinsic) pathways both activate the final common pathway of factor X, thrombin and fibrin.
Thromboplastin, also known as tissue factor, is released from damaged tissues or activated platelets during blood vessel injury. It initiates the extrinsic pathway of the coagulation cascade by forming a complex with coagulation factor VII, triggering the cascade that ultimately leads to the formation of a blood clot.
The Extrinsic Pathway
True. The extrinsic pathway of blood clotting is triggered by external factors and occurs more quickly than the intrinsic pathway, which is initiated by internal factors.