OSMT (Ontario Society of Medical Technologists) Practice Exam

A blood clot is primarily composed of fibrin, which is a fibrous protein that forms a mesh-like structure to stabilize the clot and prevent further bleeding. When a blood vessel is injured, the clotting process is initiated, which includes the conversion of fibrinogen—a soluble plasma protein—into fibrin, an insoluble protein. This conversion is facilitated by the enzyme thrombin, which acts on fibrinogen during the coagulation cascade.

While thrombin and fibrinogen are essential components of the clotting process, they are not the final structural component of the clot itself. Thrombin is responsible for the conversion process, and fibrinogen serves as the precursor to fibrin. Prothrombin activator is part of the cascade leading to thrombin formation, but it is also not part of the clot structure.

Thus, the correct answer reflects the actual substance that constitutes the fibers creating the supportive matrix of the blood clot, making fibrin a critical element in the prevention of excessive bleeding.