Stroke is a disease that affects the vessels supplying blood to the brain, according to the American Heart Association. Oxygen deprivation because of interrupted or reduced blood supply to the brain causes a stroke. A stroke can also form from too much blood in the brain. Risk factors for stroke include high blood pressure, high cholesterol and poor lifestyle habits, such as smoking.
Reduced Blood Flow
Ischemic strokes account for 80 percent of occurrences, and they stem from blockage and narrowing of the arteries to the brain, according to the Mayo Clinic. A blockage reduces blood flow, causing brain cell death because of oxygen and nutrient deprivation. Thrombotic and embolic strokes most commonly cause reduced blood flow. A thrombus is a clot formation in an artery that supplies blood to the brain. The arteries become clogged because of plaque accumulation. The National Institute of Neurological Disorders and Stroke notes that people at higher risk for clogged arteries include smokers, those with mismanaged diabetes and those who are obese. An embolus is a mass or foreign body that passes through the bloodstream, lodges in a blood vessel and blocks it. Often, this is a blood clot in a part of the body away from the brain, such as in the heart, and is swept through your bloodstream to lodge in narrower brain arteries. Irregular beating in the two upper chambers of the heart, called atrial fibrillation, frequently is the cause.
Ruptures and Bleeding
A hemorrhagic stroke refers to bleeding resulting from leakage or rupture of vessels in the brain or diseased arteries that burst in the brain. The American Heart Association recognizes two types of cerebral hemorrhages: subarachnoid and intracerebral. In subarachnoid hemorrhages, an aneurysm, or rupture, causes excess bleeding that starts in the large artery near the surface of the brain and then spills into the space between the brain and skull. Intracerebral hemorrhages occur when the blood vessel in the brain bursts and the excess blood spills into the surrounding brain tissue. High blood pressure often leads to the intracerebral hemorrhages. They often cause death because of the increased pressure in the brain from severe bleeding.
Temporary Decrease of Blood
Mini-strokes--transient ischemic attacks, or TIAs--occur when blood supply decreases temporarily. Clots blocking blood flow cause TIAs. This minor form of stroke does not last long, but often indicates a higher risk of full stroke. The Mayo Clinic notes that TIA symptoms can last for a few minutes up to a full day, and may include sudden, severe headache, numbness on one side of the body and blurred vision. Regarding TIAs as a warning sign can help prevent a future stroke if a person seeks medical intervention and makes lifestyle changes.
