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Coagulation

General

Intrinsic pathway


Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 9 June 2012, last major update June 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.

General
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● Involves factors VIII, IX, XI, XII (Hageman factor), prekallikrein, high molecular weight kininogen (Wikipedia)
● 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

Diagrams
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Intrinsic pathway

Additional references
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● Kolde, Hans-Jurgen (2004). Haemostasis. Basel, Switzerland: Pentapharm Ltd.

End of Coagulation > General > Intrinsic pathway


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