Depicted here is the formation of a thrombus (blood clot) because of the rupture of an atherosclerotic plaque. The plaques are focal changes in the vessel wall. They are formed by hardening and thickening of vessel walls and by deposition of fatty masses. If the surface of a plaque tears, the substances that were contained inside the plaque (see yellow structures in the middle) can get into the vessel and may occlude it. In front of the plaque material red blood-cells are piling up.