Of Extrinsic Ani ) Intrinsic Pathways

Bq II. L. NO55EL T MECHANISMS, the extrinsic and the intrinsic, have been defined whereby in vitro blood coagulation may be initiated. The extrinsic system is initiated by tissue thromboplastin which, in the presence of Factor VII and calcium, activates Factor X (Stuart-Prower factor).’5 The intrinsic system is initiated by foreign surface contact which results in sequential activation of Factors XII ( Hageman factor ) , XI ( PTA-Plasma thromboplastin antecedent), and IX (Christmas factor or PTC-plasma thromboplastin component).61C The extent to which these activation mechanisms function in vivo is unknown and methods are required for identifying the occurrence of the different reactions which initiate the two pathways. Previous studies have shown that activation of Factors XI and IX by foreign surface contact is associated with directly proportional consumption of these factot.s,’3’4 and that serum derived from blood clotted with tissue thromboplastin has a low Factor X content.’1 The consumption of coagulation Factors IX, X, and XI resulting from activation of the intrinsic and extrinsic pathways was studied to determine whether the two activation mechanisms result in different patterns of coagulation factor utilization. The results of these studies are reported in this paper.