Describe the intrinsic and extrinsic pathways of clot formation

Describe the intrinsic and extrinsic pathways of clot formation and breakdown. Begin at the point of tissue injury. How do the laboratory tests PT (prothrombin time) and PTT (partial thromboplastin time) evaluate the extrinsic and intrinsic pathways of clotting, and how are those measurements altered by drugs used to treat states of excess clotting?