Coagulation Cascade Explained

Haemostasis: The Body's Response to Vascular Injury

Overview of Haemostasis

• Haemostasis is the physiological process that limits blood loss following vascular injury, involving activated platelets, red blood cells, and fibrin.

• The formation of blood clots is mediated by approximately 30 proteins known as clotting factors.

Initiation of Platelet Activation

• Vascular injury exposes collagen and von Willebrand factor from the vessel wall, leading to platelet adhesion and partial activation.

• Activated platelets change shape and release signaling molecules that recruit additional platelets to the injury site.

• Tissue factor plays a crucial role in initiating the coagulation cascade upon contact with Factor 7a and Factor 10a in the bloodstream.

Coagulation Cascade and Thrombin Production

• The interaction between tissue factor and clotting factors results in a small amount of thrombin production, which fully activates platelets.

• One molecule of Factor Xa can generate up to 1000 molecules of thrombin through a cascade effect on the platelet surface.

Formation of Fibrin Clot

• Thrombin converts fibrinogen into insoluble fibrin strands at the site of injury while activating Factor XIII for crosslinking fibers.

• The resulting fibrin mesh stabilizes the clot by trapping more platelets and red blood cells, promoting further growth.

Breakdown of Clot (Fibrinolysis)

• As vessel integrity is restored, endothelial cells secrete tissue plasminogen activator, which activates plasmin to degrade fibrin.