- This page deals with the cessation of life. For other meanings of death, see death (disambiguation).
Death is either the cessation of life in a living organism or the state of the organism after that event. A common symbol of death is a grim reaper or the color black. The grave is a metonym for death.
Biologically, death can occur to wholes, to parts of wholes, or to both. For example, it is possible for individual cells and even organs to die, and yet for the organism as a whole to continue to live; many individual cells can live for only a short time, and so most of an organism's cells are continually dying and being replaced by new ones.
Conversely it is also possible for the organism to die and for cells and organs to live and to be used for transplantation. In the latter case, though, the still-living tissues must be removed and transplanted quickly or they too will soon die without the support of their host. Rarely, cell cultures can be immortal as in the case of Henrietta Lacks HeLa cell line.
Irreversibility is often cited as a key feature of death. Accordingly by definition it would not be possible to bring an organism back to life; if an organism lives, this implies that it has not died earlier, even if that seemed the case. Nonetheless, many people do not believe that death is always and necessarily irreversible; thus some have a religious belief in bodily or spiritual resurrection, while others have hope for the eventual prospects of cryonics or other technological means of reversing death.
It has been hypothesized that a limited lifespan is a consequence of evolution not selecting for extreme longevity in most species, as evolutionary selection only need apply to the organism up to the point of reproduction; after that, except for caring for kin, the continued existence of an individual can have little effect on the survival of its gene line.
Human death: definitions and significance
By far the most important sort of death to human beings is human death. Thinking about human death raises a number of questions.
First, how can we identify the exact moment at which death has occurred? This seems important, because identifying that moment would allow us to put the correct time on death certificates, make sure that the deceased's will is enacted only after the deceased is truly deceased, and in general guide us regarding when to act as one should act toward a living person and when to act as one should toward a dead person. In particular, identifying the moment of death is important in cases of organ transplant, as organs must be harvested as quickly as possible after death.
Historically, attempts to define the exact moment of death have been problematic. Death was once defined as the cessation of heartbeat (cardiac arrest) and of breathing, for example, but the development of CPR and early defibrillation posed a challenge: either the definition of death was incorrect, or techniques had been discovered that really allowed one to reverse death (because, in some cases, breathing and heartbeat can be restarted). Generally, the first option was chosen. (Today this definition of death is known as "clinical death".)
Today, where a definition of the moment of death is required, we usually turn to "brain death" or "biological death": people are considered dead when the electrical activity in their brain ceases. It is presumed that a stoppage of electrical activity indicates the end of consciousness. However, those maintaining that only the neo-cortex of the brain is necessary for consciousness sometimes argue that only electrical activity there should be considered when defining death. In most places the more conservative definition of death (cessation of electrical activity in the whole brain, as opposed to just in the neo-cortex) has been adopted (for example the Uniform Definition of Death Act in the United States). However, in all cases the common cause of death is anoxia.
Even in these cases, the determination of death can be difficult. EEGs can detect spurious electrical impulses when none exists, while there have been cases in which electrical activity in a living brain has been too low for EEGs to detect. Because of this, hospitals often have elaborate protocols for determining death involving EEGs at widely separated intervals.
Medical history contains many anecdotal references to people being declared dead by physicians and coming back to life, sometimes days later in their own coffin or when embalming procedures are about to get underway. Stories of people actually being buried alive (which must assume embalming has not occurred) led at least one inventor in the early 20th Century to design an alarm system that could be activated from within the coffin.
Because of the difficulties in determining death, under most emergency protocols, a first responder is not authorized to pronounce a patient dead; some police training manuals, for example, specifically state that a person is not to be assumed dead unless there is clear and obvious indications that death has occurred, such as decapitation or extreme damage to the body. If there is any possibility of life and in the absence of a do not resuscitate order, emergency workers must begin rescue and not end it until a patient has been brought to a hospital to be examined by a physician. This frequently leads to situation of a patient being pronounced dead on arrival.
It is also possible that death does not occur at a particular moment, but unfolds as a process over a period of time. Under this definition, the term "exact moment of death" loses meaning.
Cause of death in the United States
The cause of death in certain area and certain group of ages are different according to area and each group. In 2001 in U.S. the top 10 cause of death in medicine are:
Heart Disease: 696,947
- Chronic lower respiratory diseases : 124,816
Accidents (unintentional injuries): 106,742
Alzheimer's disease: 58,866
Nephritis, nephrotic syndrome, and nephrosis: 40,974
- (There were also 16,110 people murdered)
Statistical data from: U.S. Department of Health & Human Services
What happens to humans after death?
Second is the question of what, apart from the cessation of metabolism and the onset of physiological processes of decay, happens, especially to humans, during and after death (or "once dead", thinking of death as a permanent state). In particular, there is the question of what becomes of consciousness or the soul. Such questions are of long standing, and belief in an afterlife is common and ancient (see underworld). For many, belief in and information about an afterlife is a consolation in connection with the death of a beloved one or the prospect of one's own death. On the other hand, fear of hell or other negative consequences may make death worse. Human contemplation about death is an important motivation for the development of organized religion.
Traditions exist across most cultures to mourn the death of loved ones. Many anthropologists feel that the careful burials among Homo neanderthalensis, where ornamented bodies were laid in carefully dug, flower-strewn graves, is evidence of early belief in an afterlife. See the afterlife article for a more thorough treatment of these topics.
Physiological consequences of human death
For the human body, the physiological consequences of death follow a recognized sequence through early changes into bloating, then decay to changes after decay and finally skeletal remains.
The changes in the immediate post-death stage have received the most attention for two reasons - firstly it is the stage mostly likely to be seen by the living and secondly because of the research of forensics in potential crimes.
Soon after death (15 to 120 minutes depending on various factors) the body begins to cool (algor mortis), becomes pallid (pallor mortis ), and internal sphincter muscles relax leading to the release of urine, feces, and stomach contents if the body is moved. The blood moves to pool in the lowest parts of the body, livor mortis (dependent lividity), within thirty minutes and then begins to coagulate. The body experiences muscle stiffening, rigor mortis, which peaks at around twelve hours after death and is gone in another twenty-four, depending on temperature. Within a day the body starts to show signs of decomposition (decay), both autolytic changes and from 'attacking' organisms - bacteria, fungi, insects, mammalian scavengers, etc. Internally the body structures begin to collapse, the skin loses integration with the underlying tissues, and bacterial action creates gases which cause bloating and swelling. The rate of decay is enormously variable; a body can be reduced to skeletal remains in days, or remain largely intact for thousands of years.
In most cultures, before the onset of significant decay, the body is ritually disposed of, usually either cremated or deposited in a tomb, often a hole in the earth called a grave, but also in a sarcophagus, a crypt, sepulchre, or ossuary, a mound or barrow, or endlessly monumental surface structures, a mausoleum such as the Taj Mahal. In certain cultures efforts are made to retard the decay processes before burial, mummification or embalming. This happens during or after a funeral ceremony. Many funeral customs exist in different cultures.
A new alternative is "ecological burial": this involves subsequently deep-freezing, pulverisation by vibration, freeze-drying, removing metals, and burying the resulting powder, which has 30% of the body mass. 
Graves are usually grouped together in a plot of land called a "cemetery" or a "graveyard" and can arranged by a funeral home or undertaker or by a church.
Personification of death
Main article: Death (personification)
Death is also a popular mythological figure who has existed in mythology and popular culture since the earliest days of storytelling. The traditional western image of Death, known as the Grim Reaper, is employed in modern culture on a tarot card and in various television and film works. A form of this personification is a major character in the Discworld series by Terry Pratchett, with many of the novels centering around him as the main character. An unusual personification of Death appears in Neil Gaiman's Sandman graphic novels. Another famous appearance of death is in Ingmar Bergman's The Seventh Seal, in which the protagonist plays a game of chess against Death on the beach - this scene is parodied in the film Bill and Ted's Bogus Journey. In the webcomic Jack, Death is a large green anthropomorphic rabbit known as Jack who also pulls double duty as the Sin of Wrath.
The mortality rate is the measure of number of deaths per total number of persons in a given area and time. An example would be 2 deaths per 10,000 people per year.