Pop goes the cell

Not being a biology student, I've always only wondered what 'death' was, among other biologyie things. When I was younger, some films show some kind of white plasma flying towards the sky, leaving the lifeless body to symbolize death. The Max Excel fellow also believes in some gas called "praana-vaayu" (which he denied was oxygen) that keeps a man alive and is lost when he is dead. How this gas decides when the cells are appropriately damaged to depart, I never gotten round to ask. I must've also asked how they explained away organ-death, or, more fundamentally, cell-death. These deaths don't require the individual as a whole to die. Or, more interestingly, how do they fit in organ-transplantation which works because an organ doesn't die, while the individual dies. They probably would've come up with a multi-celled soul perhaps. But AFAIK, almost all religious people believe some kind of soul/plasma as the 'essence' of life. And that's the religious description of death, while what I am interested is in the scientific one.

So, when is a person dead?
Death, atleast biologically speaking, is a process rather than an event. But it's this irreversiblity (point-of-no-return) which is commonly referred to when one speaks of death. This point keeps getting closer to total death as technology progresses and our biological knowledge grows. This has led to many trials as to when a person is dead, legally. Of course, when you see someone with their entrails and grey matter spilling out onto the pavement, or decapitaed, or incinerated, they are properly dead. What we are interested, rather, is in determining this rubicon. Like someone said,
"Death is certain, since it is inevitable, but also uncertain, since its diagnosis is sometimes fallible"
(Note that I am not interested in the religious or legal death of a person, but the medical death.)

Is he dead when his lungs stop breathing? No. Mouth-to-mouth resuscitation can sometimes start the process. And iron-lungs can replace its work. Infact, a person may stop breathing for a few seconds several times during sleep. The extreme case, called sleep apnea, can be fatal.
Is he dead when his heart stops beating? No, not always. Remember "stand clear!" when someone uses the defibrillator and CPR in med-fictions? IOW, heart can be rebooted and even kept running afterwards with a pacemaker. Artificial hearts can also completely replace the heart.
Is he dead when both his lungs AND heart decide to stop? No, since the brain may be living and the body can be kept living in a life-support system for as long as anyone pays for it. Of course, if the episode was caused by brain death, then this argument is moot.
Is he dead when his cerebral cortex is dead? Not necessarily, but the individual as we know him is dead, because the cerebral cortex is the seat of thinking, personality, memory and the like. But we still have a living human being. Even sleep and coma can make this part of the brain appear dormant, though it's not the same as being dead and can be distinguished using an EEG.
Is he dead when his brain stem is dead? Yes (finally!). When this part is dead, the whole of the brain is dead. Note that, his other cells may still be alive. But even here, the cessation of brain activity must be for a period of time for it to be certain. When this death is not used as the ultimate indicator of death, you see people who decide to "rise from the grave" or "doing a jesus". Infact, beheaded chickens and other fowls may sometimes cluck around forever (if fed properly intravenously) as if nothing has happenned, because their brain stems are located a bit below the head. But of course, they lose their chickenness and survive on reflex alone. This suggests that there are two degrees of "alivedness" to a "brained" organism: one of the memory, and the other of the fundamental control functions.


Since B-grade movies has taught us that people can be killed in more than one way, I think it would be safe to assume that animal death can fundamentally be defined to be the death of whole of its brain. The cascade of cell deaths that preceded brain death and the cascade of cell death that follows brain death are not counted as death. The actual sequence of events that makes a person dead (of natural causes, of course) is a bit too biochemical for me to follow.

Then there's another debated topic of "natural death". What exactly causes "natural expiration"? I read what telomerase is and how it's repeated shortenening when cloning/cell-division can put a limit to the count of an individual's life. But apparently it's not the only answer. But I am sticking to the life-support functions (heart, lungs, etc) stopping to enrich the brain with food.

While going bored over searching for natural death, I came across a type of Cell Death called 'Apoptosis', from which the topic for this post is derived (Apoptosis. Get it?).

Cell death:
From what I gather, there are two ways a cell may die: Necrosis, where the cell may die of starvation, physical damage, chemical poisoning, etc, and PCD, where the cell suicides if it feels 'unwanted" (cell depression?). Apoptosis is one of the main type of PCD.

A cell becomes "unwanted" when new cells are ready to take it's place, or if it becomes damaged beyond repair by toxins or pathogens, or if it's apoptosis code in it's DNA is triggered by damage, virii, xrays, etc. And, as the name implies, each cell is embedded with the suicide sequence which can be initiated by one of the contributing factors mentioned above.

Contrary to what I thought, apoptosis occurs normally quite abundantly in a normal human adult. Homeostasis, a greek for the balance between old cells and newly produced cells, is an active balance that needs apoptosis to work. Infact, over 50 to 70 billion cells are produced each day and the same amount of cell has to die each day to compensate. If not, a cancerous tumour results. OTOH, if more cells die, I don't have a greek word for it, but it is obviously something bad. Infact, one of the ways in which HIV succeeds is by apoptosis of immuno cells. With so many cells getting replaced, the human body rotates an equivalent of it's own body weight in one year, it seems. Apart from homeostasis, the other important function of apoptosis is in differentiation of individual fingers in a developing foetus. Apoptosis is your friend. [link]


Whence such a morbid topic? I was going through the straightdope archives and found an article on being scared to death. Quite a few persons have been scared to death or willed to death. This got me scrambling for the basics on death. But the article itself provides most of the answers, which I noted only a bit later in my this research. Searching a bit late, I found this very interesting biology class discussion on death. Reading it makes me wish I had put more effort in securing an MS admission in an US university. Oh well, I have but little chance now.