Clot Retraction and Fibrinolysis

The activated platelets in a blood clot extend projections and interact with other platelets and fibrin fibers.

Within 30 to 60 minutes, the contractile proteins in these platelet projections start pulling the fibrin strands to initiate clot retraction.

As a result, the clot reduces in size, bringing the edges of the damaged vessel closer together.

Simultaneously, platelets primarily release two growth factors to stimulate different cell types for injury repair.

Platelet-derived growth factor promotes cell division and growth of the smooth muscle and fibroblasts from the surrounding connective tissue to rebuild the vessel wall.

On the other hand, the vascular endothelial growth factor restores the endothelial lining of the blood vessel.

As the injury heals, the neighboring endothelial cells secrete tissue plasminogen activator, which activates a plasma protein called plasminogen trapped within the fibrin mesh.

The activated plasminogen, called plasmin, breaks down the clot by digesting fibrin threads. This process, called fibrinolysis, starts within two days of clot retraction and clears the vessel.