intrinsic pathway of blood coagulation

Last reviewed 01/2018

After initiation, each step in the intrinsic pathway is catalysed by the product of the preceding step:

  • factor XII, also termed Hageman factor, is converted to XIIa on contact with negatively-charged surfaces e.g. that of subendothelial collagen. For activation to its enzymatic form, it requires high molecular weight kininogen and prekallikrein.
  • factor XIIa converts factor XI to XIa
  • factor XIa converts factor IX converted to IXa
  • factor IXa converts factor X to Xa; to do this it requires:
    • calcium ions
    • factor VIIIa
    • a negatively charged surface; in vivo, this is the surface of platelets so localizing the cascade
  • factor Xa then activates the common pathway of coagulation