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Hemostasis is the process of stopping bleeding through the formation of a platelet plug and a fibrin clot, strictly controlled to avoid both hemorrhage and pathological thrombosis. The coagulation cascade is an enzymatic amplification network: each factor activates multiple molecules of the next, with positive feedback (thrombin activates factors VIII and V) slowed by natural inhibitors (AT-III, TFPI, protein C).

The endogenous thrombin potential (ETP, area under the thrombin generation curve) synthesizes the global state of coagulation: elevated ETP indicates hypercoagulability (thrombophilia, antiphospholipid syndrome, cancer); Reduced ETP indicates hypocoagulability (hemophilia, anticoagulant treatment). Hemker's kinetic model quantifies the three phases: initiation (lag phase, 05 min), amplification (thrombin peak, 510 min), and termination (inhibition, > 10 min).

Virchow's triad (stasis, hypercoagulability, endothelial injury) is the pathophysiological model of deep vein thrombosis (DVT) and pulmonary embolism (PTE). Fogelson's model describes thrombus propagation as an advection-diffusion-reaction problem: platelets are transported by flow (u) and diffusion (D_plaq) towards the adhesion zone, where they bind to subendothelial collagen. Low flow (stasis: Re < 100) favors the accumulation of activated coagulation factors.

Fibrinolysis (clot dissolution) is mediated by plasmin, which cleaves fibrin. t-PA (tissue plasminogen activator, used in the treatment of stroke and AMI) converts plasminogen to plasmin with first-order kinetics: clot lysis continues t½ 1030 min for therapeutic doses of t-PA, but the risk of bleeding increases with the dose.

Oral anticoagulation (warfarin) is monitored with the INR: INR = (TP_pac/TP_norm)^ISI, where ISI depends on the reagent used. The therapeutic range (INR 23 for atrial fibrillation or DVT) balances antithrombotic efficacy and bleeding risk. The new direct oral anticoagulants (DOACs) directly inhibit factor Xa (rivaroxaban) or thrombin (dabigatran) with a more predictable effect and without the need for routine monitoring.

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