Activated Factor X is the first step in which coagulation pathway?

Activated Factor X is a crucial point in the coagulation cascade that signifies the commencement of the common pathway. In the coagulation process, Factor X, when activated (denoted as Xa), serves as a pivotal enzyme that catalyzes the conversion of prothrombin to thrombin. Thrombin, in turn, plays a significant role in furthering the cascade by converting fibrinogen to fibrin, which is essential for clot formation.

The coagulation cascade is generally divided into three pathways: intrinsic, extrinsic, and common. The intrinsic and extrinsic pathways activate several factors that eventually converge at Factor X, leading to the activation of the common pathway. The common pathway is critical because, regardless of the initial stimulus (from either the intrinsic or extrinsic pathways), it leads to the formation of a stable fibrin clot.

Thus, by choosing the common pathway, one recognizes the essential role of activated Factor X as the unifying point that links both the intrinsic and extrinsic pathways to the final common steps of coagulation.