Intrinsic pathway

Topic Completed: 1 June 2012

Minor changes: 14 December 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Intrinsic pathway [title] coagulation

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Cite this page: Parsons, J. Intrinsic pathway. website. Accessed June 7th, 2020.
Definition / general
  • Involves factors VIII, IX, XI, XII (Hageman factor), prekallikrein, high molecular weight kininogen (Wikipedia - Coagulation)
  • Merges with extrinsic pathway into common pathway
  • Activated when factor XII binds to negatively charged "foreign" surface exposed to blood
  • Then sequentially activates factors XI, IX, X, then factor II (prothrombin to thrombin), which converts fibrinogen to fibrin (see common pathway)
  • Once extrinsic pathway is inhibited by TFPI-Xa complex (see extrinsic pathway), factor VIIIa / IXa complex becomes dominant generator of factor Xa, thrombin and fibrin
  • Factor XIIa also converts prekallikrein to kallikrein, which activates more factor XIIa
    • Both require high molecular weight kininogen as cofactors
  • Kallikrein also releases bradykinin from high molecular weight kininogen, which causes vasoconstriction
  • The activated partial thromboplastin time (aPTT) measures the intrinsic and common pathways
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Intrinsic pathway

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