Thrombosis is the formation of a blood clot, called a thrombus, inside an intact blood vessel. Normally blood only clots where a vessel has been damaged and is open to the outside. A thrombus inside a vessel can block the flow of blood.How a thrombus forms in an artery. An atheroma can grow and break through the endothelium, leaving a rough surface and exposing the collagen and damaged tissue underneath. Platelets stick to the exposed area, and the clotting cascade is triggered. A mesh of fibrin forms, trapping red blood cells and platelets, and a thrombus builds up on the plaque. This narrows the artery further and may block it completely.Emboli. Part of a thrombus can break away and be carried in the bloodstream. A clot travelling in the blood is called an embolus. It can lodge in a smaller vessel further along and block it, cutting off the blood supply to the tissue beyond. This is called an embolism.Deep vein thrombosis (DVT). Clots can also form in the deep veins of the legs, especially when a person sits still for long periods, such as on long flights, because blood flow in the leg veins is slow. Part of the clot may break off and travel to the lungs.
Prevention. Anticoagulant drugs, such as warfarin and heparin, reduce the ability of the blood to clot. Aspirin reduces the risk of thrombosis by making platelets less sticky. These drugs increase the risk of bleeding, so doses must be controlled carefully.
Prevention. Anticoagulant drugs, such as warfarin and heparin, reduce the ability of the blood to clot. Aspirin reduces the risk of thrombosis by making platelets less sticky. These drugs increase the risk of bleeding, so doses must be controlled carefully.