Which coagulation factor collaborates with thrombin in the conversion of fibrinogen?

The correct factor that collaborates with thrombin in the conversion of fibrinogen to fibrin is Factor V. Thrombin plays a crucial role in the coagulation cascade, particularly in converting fibrinogen, a soluble plasma protein, into fibrin, which forms the meshwork of a blood clot. Factor V amplifies the action of thrombin, allowing for a more efficient conversion process.

In the coagulation cascade, Factor V acts as a cofactor for prothrombinase, enhancing thrombin generation. While Factors VIII, XIII, and XI are also important in the coagulation process, they serve different functions. Factor VIII acts as a cofactor for Factor IX, enhancing its ability to activate Factor X. Factor XIII is involved in cross-linking fibrin, stabilizing the clot after formation, and Factor XI activates Factors IX and X, playing an earlier role in the cascade. Therefore, Factor V's specific role in directly supporting thrombin's activity in the conversion of fibrinogen makes it the correct choice.