Chapter 18 - Section 18.5 - Study Guide - Assess Your Learning Outcomes - Page 705: 5

The extrinsic coagulation pathway is one of the two main pathways that lead to blood clot formation, and it is primarily initiated by tissue factor (TF), also known as tissue factor III. Here are the key essentials of the extrinsic coagulation mechanism: **Initiation:** Tissue factor (TF) is a protein that is released from damaged tissues outside the blood vessels, usually as a response to injury. When blood comes into contact with exposed tissue factor, it triggers the coagulation cascade. **Procoagulants Involved:** 1. **Tissue Factor (TF):** Tissue factor, as mentioned, is the primary initiator of the extrinsic pathway. It binds to and activates Factor VII, leading to the activation of the coagulation cascade. 2. **Factor VII (FVII):** Factor VII is a clotting factor that, when activated by tissue factor, becomes Factor VIIa. This activated form plays a critical role in the extrinsic pathway by initiating a series of reactions. **Convergence with the Intrinsic Pathway:** The extrinsic pathway converges with the intrinsic pathway at a common intermediate, which is the activation of Factor X (Factor Xa). Factor X is a central component of the coagulation cascade that marks the entry into the common pathway leading to fibrin clot formation. The activation of Factor X involves the action of both the extrinsic and intrinsic pathways. **Point of Convergence:** At the point of convergence, Factor VIIa, which is activated by tissue factor in the extrinsic pathway, activates Factor X. This activation of Factor X marks the transition from the extrinsic pathway to the common pathway of coagulation. Once Factor X is activated, it leads to a series of reactions that ultimately result in the conversion of prothrombin to thrombin. Thrombin then converts fibrinogen into fibrin, forming the stable fibrin clot. In summary, the extrinsic coagulation pathway is initiated by tissue factor released from damaged tissues. This pathway involves the activation of Factor VII and ultimately converges with the intrinsic pathway at the activation of Factor X, which is a critical step in the formation of the fibrin clot. The combined actions of the extrinsic and intrinsic pathways ensure effective hemostasis and blood clot formation in response to vascular injury.

The extrinsic coagulation pathway is one of the two main pathways that lead to blood clot formation, and it is primarily initiated by tissue factor (TF), also known as tissue factor III. Here are the key essentials of the extrinsic coagulation mechanism: **Initiation:** Tissue factor (TF) is a protein that is released from damaged tissues outside the blood vessels, usually as a response to injury. When blood comes into contact with exposed tissue factor, it triggers the coagulation cascade. **Procoagulants Involved:** 1. **Tissue Factor (TF):** Tissue factor, as mentioned, is the primary initiator of the extrinsic pathway. It binds to and activates Factor VII, leading to the activation of the coagulation cascade. 2. **Factor VII (FVII):** Factor VII is a clotting factor that, when activated by tissue factor, becomes Factor VIIa. This activated form plays a critical role in the extrinsic pathway by initiating a series of reactions. **Convergence with the Intrinsic Pathway:** The extrinsic pathway converges with the intrinsic pathway at a common intermediate, which is the activation of Factor X (Factor Xa). Factor X is a central component of the coagulation cascade that marks the entry into the common pathway leading to fibrin clot formation. The activation of Factor X involves the action of both the extrinsic and intrinsic pathways. **Point of Convergence:** At the point of convergence, Factor VIIa, which is activated by tissue factor in the extrinsic pathway, activates Factor X. This activation of Factor X marks the transition from the extrinsic pathway to the common pathway of coagulation. Once Factor X is activated, it leads to a series of reactions that ultimately result in the conversion of prothrombin to thrombin. Thrombin then converts fibrinogen into fibrin, forming the stable fibrin clot. In summary, the extrinsic coagulation pathway is initiated by tissue factor released from damaged tissues. This pathway involves the activation of Factor VII and ultimately converges with the intrinsic pathway at the activation of Factor X, which is a critical step in the formation of the fibrin clot. The combined actions of the extrinsic and intrinsic pathways ensure effective hemostasis and blood clot formation in response to vascular injury.