Thrombosis is the process of a blood clot, also known as a thrombus, forming in a blood vessel. This clot can block or obstruct blood flow in the affected area, as well as cause serious complications if the clot moves to a crucial part of the circulatory system, such as the brain or the lungs. It is normal for the body to produce clotting factors like platelets and fibrin when a blood vessel is injured, to prevent an excessive loss of blood from the body. If this effect is over productive it can obstruct the flow of blood and form an embolus that moves around the blood stream. Thrombosis can be broadly classified as either venous thrombosis or arterial thrombosis, according to where the thrombus presents in the body. Venous thrombosis occurs in the veins and is categorized further according to where it occurs including: Deep vein thrombosis, Portal vein thrombosis, Renal vein thrombosis, Jugular vein thrombosis, Budd-Chiari Syndrome, Paget-Schoetter disease, Cerebral venous sinus thrombosis, Arterial thrombosis, also known as atherothrombosis due to its association with atheroma rupture, occurs in the arteries. The blood stasis caused by atrial fibrillation may also cause this type of thrombosis. There are multiple causes for stroke, including ischemia, hemorrhage and embolus in the brain. Stroke due to a blood clot in the brain usually builds gradually around an atherosclerotic plaque. Myocardial infarction may also be caused by a thrombus in the coronary artery and is associated with ischemia. The reduced oxygen supply to the heart cells, as a result of the blockage, results in cell death and myocardial infarction.