Final answer:
The extrinsic pathway of blood coagulation begins with the release of tissue factor from damaged cells and rapidly culminates in the activation of Factor X, leading into the common coagulation pathway for clot formation.
Step-by-step explanation:
Extrinsic Pathway of Blood Coagulation
The extrinsic pathway is a crucial component of the blood coagulation process that is rapidly initiated following traumatic tissue injury. It starts with the release of tissue factor (Factor III) from damaged cells, which interacts with blood plasma. Subsequently, the presence of calcium ions (Ca²+) and Factor VII (proconvertin) leads to the formation of an enzyme complex. This complex acts on Factor X (Stuart-Prower factor), resulting in its activation, which in turn powers the common pathway of clotting and is swiftly finalized, often within seconds.
Role of Vitamin K and Calcium
Both vitamin K and calcium play essential roles in the clotting process. Vitamin K is required for the synthesis of certain clotting factors by the liver, while calcium (Factor IV) acts as a cofactor in various steps of the coagulation pathways. Adequate dietary intake, along with endogenous synthesis by intestinal bacteria, ensures sufficient levels of these components for proper function.
Common Pathway Convergence
The intrinsic and extrinsic pathways converge at the common pathway, where the activated Factor X, along with prothrombinase, catalyzes the conversion of prothrombin (Factor II) to thrombin. Thrombin then transforms fibrinogen (Factor I) into insoluble fibrin strands, which are subsequently stabilized by Factor XIII, therefore culminating in the formation of a blood clot.