Final answer:
In the intrinsic pathway of blood clotting, factor XII is activated and sets off a series of reactions that activate factor XI and factor IX. Finally, a complex formed by factor VIII and factor IX activates factor X.
Step-by-step explanation:
In the intrinsic pathway of blood clotting, factor XII (Hageman factor) is activated when it encounters negatively charged molecules in the bloodstream. This activation sets off a series of reactions that activate factor XI and factor IX. Additionally, chemicals released by platelets increase the rate of these activation reactions. Finally, a complex formed by factor VIII and factor IX activates factor X, which leads to the common pathway of blood clotting.