Coagulation Flashcards
What are the the phases of cell based model of coagulation?
Initiation
Amplification and
Propagation
Described the steps in cell based model of coagulation
INITIATION - constantly occurring to prime tissues in preparation for bleeding, low level tissue factor activity as it present on the interstitial cell surfaces. Can bind Factors 7, 10 and prothrombin resulting in the generation of small amounts of thrombin.
AMPLIFICATION - Damage to blood vessels results in TF exposure, which reacts with platelets to activate them. The exposed TF also activates other clotting factors, especially factor 5 and 11, the net result being platelets are coated in clotting factor.
PROPAGATION - Factor 9a is generated by the TF/Factor 7a complex located on the surface of TF-expressing cells. By combining with its co-factor, 8a on the surface of the platelets, factor 9a is responsible for activating factor 10. The activation of factor 10 to factor 10a results in the combination of 10a with its cofactor 5a, which in turn leads to the production of large quantities of thrombin.
Thrombin then converts fibrinogen into fibrin.
The fibrin structure of the clot is then stabilised by covalent bonding under the influence of factor 13.
What are the main features of the classical model of coagulation?
This is a proteolytic pathway in which there are two pathways, extrinsic and instrinsic pathways which lead to a common pathway.
Intrinsic pathway - activated when in contact with damaged sub-endothelial connective tissue. Starts with Factor 12-12a, 11-11a, 9-9a, combines with factor 13, to reach common pathway which converts 10-10a. Slower pathway of the two.
Extrinsic pathway - The extrinsic pathway is an alternative route for the activation of the clothing cascade. It provides a very rapid response to tissue injury, generating activated factor X almost instantaneously,
In the common pathway, the main product is thrombin from prothrombin, and fibrinogen to fibrin forming a fibrin clot.
