Fibrin << FY bruhn >> is a white, fibrous protein substance that makes up the most important part of a blood clot. Fibrin is formed from fibrinogen, a protein found in the blood. When a blood vessel is damaged, a series of chemical reactions causes fibrinogen to coagulate (thicken) into strings of fibrin that form a mesh at the site of the damage. Red blood cells and cells called platelets combine with the fibrin to form a clot. Clots may also form inside a blood vessel and stop the flow of blood through it. Such clots can lead to heart attacks, strokes, and other life-endangering conditions.
