Tissue factor pathway inhibitor acts on which pathway, and on which conversion?

1. The name itself points to the target, since tissue factor is factor III, the starter of the extrinsic pathway. 2. Tissue factor pathway inhibitor therefore acts on the extrinsic pathway. 3. Within that pathway it inhibits the conversion of inactive factor VII to the active form. 4. Blocking factor VII stops the enzyme complex forming and so stops factor X being activated by this route. 5. Factors XII and VIII are intrinsic pathway members, so both intrinsic options name the wrong limb. 6. Factor XIII is the fibrin stabiliser in the common pathway, well downstream of anything tissue factor inhibitor touches. 7. Note that inhibiting one limb still leaves the other able to reach factor X, which is why anticoagulation of a single pathway limits rather than abolishes clotting. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 18 "The Cardiovascular System: Blood", section 18.5 Hemostasis_