The human body possesses a complex clotting mechanism designed to help control bleeding excessive bleeding. Many of the bimolecular components found within the clotting pathway are dependent on vitamin K. Warfarin is a prescription drug that is commonly used to prevent blood clots and achieves this effect by inhibiting the synthesis of vitamin K dependent coagulation factors.
Extrinsic System
Within the extrinsic system of the coagulation pathway, vitamin K is required for the synthesis of coagulation factor VII. In combination with tissue factors and additional coagulation factors, the extrinsic system is responsible for the activation of factor X, which is also dependent on vitamin K. Activated factor X is then utilized within the common system to promote the formation of clots.
Common System
Vitamin K is also required for the synthesis of prothrombin, also known as coagulation factor II. Prothrombin is part of the common system in the coagulation pathway and is converted to thrombin by activated factor X. The role of thrombin is to convert fibrinogen to fibrin which cross link to form a clot that helps to stop bleeding.
Intrinsic System
The intrinsic system is a unique cycle within the coagulation pathway. Activated factor X in the common system also activates vitamin K dependant coagulation factor IX. As a result, activated factor IX then acts at an earlier part of the coagulation pathway to activate additional factor X, thereby repeating the intrinsic cycle.
Proteins C and S
Plasma proteins C and S are also dependent on vitamin K for synthesis. In contrast to coagulation factors, proteins C and S act by inhibiting the formation of thrombin. In response to thrombin formation, proteins C and S inactivate coagulation factors V and VIII within the pathway to prevent excessive clotting. Patients should speak with a physician with concerns regarding blood clots and anticoagulation medications.
References
- Bristol-Myers Squibb: Coumadin Package Insert
- University of Alabama-Birmingham Department of Pathology: Overview of the Coagulation Cascade
- "Activated Protein C Cofactor Function of Protein S: A Critical Role for Asp95 in the EGF1-like Domain," Blood. Helena M. Andersson, et al. (Jun. 2010)
Member Comments