extrinsic pathway of the coagulation cascade
occurs outside of blood vessels due to exposure to subepithelial components; requires calcium; involves activation of factor VII to factor VIIa using factor Xa; factor VIIa then activates factor X to Xa using Tissue Factor as a cofactor; factor Xa activates prothrombin to thrombin; 'chicken and egg' situation w.r.t. factors VIIa and Xa