Regulatory Mechanisms
Tissue Factor
Pathway Inhibitor (TFPI):
TFPI binds with Factors Xa and IXa and does the following:
On intact endothelial cells a receptor for thrombin is present called “thrombomodulin”.
Protein C regulatory System:
Inhibits Factor Xa and IXa activity
Thrombomodulin binds with thrombin and this complex activates Protein C (APC)
Binds with Tissue factor-Factor VIIa complex and stops further
activation of Factors X and IX by TF-VIIa complex
APC then binds free plasma Protein S to form a APC-Protein S complex
This APC-Protein S complex then inactivates Factors Va and VIIIa