Which of the following statements about the coagulation cascade is/are true?

A. The intrinsic pathway of coagulation is the predominant pathway in vivo for hemostasis and coagulation.

C. Deficiencies of factor VIII and IX cause highly significant coagulation abnormalities.

DISCUSSION: Although it was previously held that two somewhat distinct pathways existed for the activation of the coagulation cascade, it is now recognized that the predominant mechanism for coagulation in vivo is the “extrinsic pathway.” Tissue factor is exposed in the subendothelial tissues when endothelial cell injury occurs. Tissue factor then tightly binds factor VII circulating in the plasma and activates the coagulation cascade. Factor VIII and factor IX deficiency cause the clinical syndromes of hemophilia A and hemophilia B, respectively. Both of these disorders involve very severe clinical bleeding disorders, whereas deficiencies of factor XII do not generally cause clinically significant bleeding. This further emphasizes the secondary role that the “intrinsic pathway” plays in coagulation.