Death, complete and irreversible cessation of life in an organism or part of an organism. The moment of death is conventionally accepted as the time when the heart ceases to beat, there is no breathing, and the brain shows no evidence of function. Since it is possible to resuscitate and maintain heart function and to take over breathing mechanically, the brain may suffer irreversible death while “life” is maintained artificially. In “brain death,” reversible causes have been eliminated, and there is no spontaneous breathing, no movement, and no specific reflexes seen on 2 occasions; artificial life support systems can then be reasonably discontinued. After death, enzymes begin the process of autolysis (decomposition), which later involves bacteria. In the hours following death, changes occur in muscle that cause rigidity (rigor mortis). Death of part of an organism (necrosis), such as occurs following lack of blood supply, consists of loss of cell organization, autolysis, and gangrene. The part may separate or be absorbed, but infection is liable to spread to living tissue. Cells may also die as part of the normal turnover of a structure (for example, skin or blood cells), because of compression (for example, by a tumor), or as part of a degenerative disease.
Criteria of death
The entire body does not die at the same rate; breathing and heart action may stop, but other functions may continue. In humans, for example, the kidneys, skin, bone, liver, pancreas, cornea, and heart have been transplanted into needy recipients and may continue to function for a long period. When on an artificial respirator, an individual may maintain a heartbeat. But is that person truly alive? If the respirator were turned off, how long would the person remain alive? What happens to the brain of a person maintained on a respirator? These questions have serious ethical, religious, and legal implications. The sequence of events toward the cessation of life suggests 4 stages: (1) a time of impending death, (2) a period of reversibility, with or without residual change, (3) a period of irreversibility, (4) absolute death, as set forth in the current legal definition, and (5) murder.
Causes of death
Natural death is often assumed to be due to coronary thrombosis (“heart attack”); the most common cause is ischemic (blood-starved) heart disease, though not necessarily the result of thrombosis. Other common causes of death are acute hypersensitive heart failure (that is, due to very high blood pressure), pulmonary embolism (a clot that has traveled to the lung), and subarachnoid or cerebral hemorrhage (stroke).
The principal causes of unnatural deaths are (1) mechanical violence, including traffic accidents, industrial mishaps or disasters, sexual and other forms of assault, and homicide, (2) physical agencies, such as heat, cold, electricity, or radiation, (3) deprivation involving the complete or partial lack of basic essentials, such as water, food, or warmth, and (4) poisoning (chemicals and drugs, anesthetics, intravenous infusions, and blood transfusions).