·      THROMBOSIS witIS a mass formed from blood constituents within avessel or the heart during life.blood clotting is aphysiological protective mechanism but thrombosis is apathological process hAVE serious consequences.MECHANISM OF FORMATION.1-platelet adhere to the endothelium and to each other,forming a projecting mass.the liberation of thromboplatin.2-if rate of flow is slow, as in avein,red cells are entangled so that the lumen is occluded.3-infront and behind the platelet mass, the blood stagnates.so the thrombus extends in either direction to the nearest junction.