fibrinoid

Fibrinoid is a substance that resembles fibrin, a protein crucial for blood clotting. It appears as a homogeneous, acidophilic, and refractile material. Fibrinoid is found in the walls of blood vessels and connective tissues, particularly in pathological conditions, and also normally in the placenta.1

Fibrin itself is an insoluble protein formed from fibrinogen, a soluble protein produced by the liver and found in blood plasma. When tissue damage causes bleeding, fibrinogen is converted into fibrin by the enzyme thrombin. Fibrin then forms long threads that trap platelets, creating a mass that hardens into a blood clot.2