When death occurs, blood—which carries oxygen to all the cells of the body— has stopped circulating. This stoppage may be caused by damage to the heart, which is the muscle that pumps blood throughout the body, or by damage to the brain, which gives the signals that direct the heart to do its pumping. (Other circumstances, like severe accidents, also stop blood flow.) But whatever the reason, once blood stops bringing its life-giving oxygen to the body’s billions of cells—the building blocks that make up the human body—the death of those cells starts to occur. When the brain, which is the body’s command center, goes without oxygen for about 15 minutes, all cells there die. While machines can help our lungs breathe or our hearts pump blood, no machine can assume the complex functions of the brain. Without a brain, we cannot live. Soon after a person dies, an official document called a death certificate is filled out and later filed as a record with the local government. It includes such information as time, place, and cause of death.