You are in Medical Library . An excellent, detailed article that explains who is at risk for stroke and what that risk really means. Brain cells require a constant supply of oxygen to stay healthy and function properly. Researchers are working to discover the cycle of events involved in cell death after oxygen is lost. One hypothesis begins when blood is cut off in the brain and substances known as excitatory amino acids are released.
Calcium reacts within the neurons to release harmful substances.
Another hypothesis focuses on an enzyme called PARP, which ordinarily makes minor molecular repairs. Confronted with substantial injury, however, PARP over-responds and takes up ATP, the major source of energy in cells. The cells die. A stroke is usually defined as either ischemic or hemorrhagic, depending upon whether it is caused by a blockage in an artery or by a tear in the artery's wall that produces bleeding in the brain. Ischemia means the deficiency of oxygen in vital tissues.