Category: biosynthesis
Sequential serine-protease activations producing thrombin (factor IIa) and ultimately fibrin clot. Extrinsic pathway: TF (factor III) + VIIa → activates X. Intrinsic pathway: XII → XI → IX (+ VIII cofactor) → X. Common pathway: X (+ V cofactor) → thrombin → fibrin. Vitamin-K-dependent factors (II, VII, IX, X + proteins C, S) require γ-carboxylation — warfarin target via VKORC1 (see vitamin_k_cycle). Heparin enhances antithrombin's inhibition of IIa + Xa. LMWHs (enoxaparin) selectively boost Xa inhibition. DOACs directly inhibit factor IIa (dabigatran) or factor Xa (apixaban, rivaroxaban, edoxaban) — bypassing antithrombin.