Coagulation
Physiology
Extrinsic pathway


Topic Completed: 1 June 2012

Minor changes: 16 September 2020

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed Search: Extrinsic pathway [title] coagulation

Page views in 2020: 866
Page views in 2021 to date: 50
Cite this page: Parsons JC. Extrinsic pathway. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/coagulationextrinsicpathway.html. Accessed January 22nd, 2021.
Definition / general
  • Involves tissue factor (TF), originally considered "extrinsic" to blood since it is present on cell surfaces not normally in contact with (i.e. extrinsic to) the circulatory system
  • The primary mechanism of the coagulation pathway in vivo is tissue factor binding to activated factor VII (factor VIIa)
  • TF-Factor VIIa complex activates factors X and IX (though in vivo it appears to first involve factors VIII and V from the intrinsic pathway, which then activate factors X and IX)
  • Activated factor IX activates more factor X, with cofactors activated factor VIII, anionic phospholipids (from activated platelets) and calcium
  • Activated factor X converts prothrombin to thrombin, with activated factor V, anionic phospholipids (from activated platelets) and calcium as cofactors
  • After initial activation, pathway is inhibited by the binding of tissue factor pathway inhibitor (TFPI) to factor Xa, which inhibits TF-Factor VIIa complex, and further coagulation is dependent on the intrinsic pathway
  • Merges with extrinsic pathway into common pathway
  • The prothrombin time (PT) measures the extrinsic and common pathways
Diagrams / tables

Images hosted on other servers:

Coagulation extrinsic pathway

Back to top
Image 01 Image 02