Coagulation cascade - Classical





aka Classical coagulation pathway

Comprised of 3 parts:

  • Extrinsic pathway
  • Intrinsic pathway
  • Common pathway

Extrinsic pathway

Extrinsic pathway is now called "tissue factor pathway"

Tissue damage
→ Tissue factor (TF) exposure
→ TF/VIIa complex formation
→ Factor X activation

Measured by PT / INR

Intrinsic pathway

Intrinsic pathway is now called "contact activation pathway"

Contact with negatively charged surface
→ Factor XII activation
→ Factor XI activation
→ Factor IX activation
→ Formation of XIa / VIIIa complex
→ Factor X activation

Measured by APTT

NB:

Negatively charged surface can be:

  • in vivo: collagen
  • in vitro: glass, kaolin

Common pathway

Factor Xa (with Factor Va as the co-factor)
→ Prothrombin (factor II) converted to Thrombin (factor IIa)

Thrombin leads to:

  • Fibrinogen converted to fibrin
  • Factor XIII activation

Factor XIIIa in turn stabilises the fibrin clot