I live in a 35 years old house. It is showing signs of ageing. Some doors do not operate as smoothly as before. Ceiling walls have layers peeling at places. Insulation is not effective anymore. The worst thing is that the house is no longer energy efficient. Something needs to be done. We discuss options. I bring up demolishing the house and building a new one. Though not the preferred option, we do not mind it either. The thought of demolition triggers a slight feeling of sadness because of memories of time spent in the house. It is our home after all. The house is inanimate. It never reciprocated our feelings. That’s probably why this parting does not affect us much. However, when a living being dies, even a pet dying of old age, it is a different matter altogether.
Talking about death and bereavement is never easy. Death scares the hell out of us. “Death is not only inevitable; it is controlled by the fates, programmed into the very fabric of life,” says the British biochemist and writer Nick Lane. True, the realisation that death is the only certainty in life occurs to us many times. Yet there are curiosities surrounding this certainty, some explained by science and some still being worked out.
What happens to a body after death?
Exactly when does life actually move out of a living body?
What is the root cause of death?
Let?s work on these curiosities one at a time.
What happens to a body after death? With due warning that words in the rest of this paragraph might create imageries of disgust for some, here I go. Simply stated, life processes stop when a living body dies. For instance, the machineries for waste removal, breathing and blood circulation cease to operate. When an animal is alive, the circulating blood helps maintain a high body temperature. The heart does all the hard work of pumping thick blood to every nook and corner of the body. With no circulation after death, body temperature continues to drop till it attains room temperature. Without breathing, oxygen cannot get inside. Even if the lungs had oxygen, without blood circulation there is no oxygen supply to the cells anyway. Consequently, the cells fail to produce ATP – the energy currency needed for pretty much everything our bodies do. No energy means the muscles cannot relax by breaking the bridges which under normal conditions cause them to stay rigid. So the body appendages become rigid. When the muscles eventually relax, the last bits of excreta are ejected. Blood drains out leaving the skin pale which then shrinks.
An animal body is a storehouse of bacteria. We humans too possess more bacterial cells than our own cells, most of them residing in the digestive tract. These bacteria spring into action when cells are no longer capable of offering a resistance. They begin consuming the organic resources of the body while ejecting sulphur and other gases. The odour produced attracts scavengers to the party. Tiny organisms and bacteria finish their job of decomposition leaving behind only the hard parts such as bones and teeth that undergo a slow decay.
Alright, we are done with the disgusting part. Now the second question.?Exactly when does life actually move out of a living body??This at once feels like heading towards spiritualism. We will stick to science however. The decomposition process described above happens at body and organ level and the effects can be observed using our senses – visual and olfactory. But if cell is the fundamental unit of life, shouldn’t we consider cell death as the time when life ultimately leaves an organism? This profound question does not have a straightforward answer. Billions of cells are born and billions die every day while we are alive. Cells die even when we are in the process of development before birth. Our fingers and toes, for instance, are joined by tissues in between when they first arise. The cells making up these tissues are programmed to die thus freeing up the digits while the foetus grows. Thus cell death has been occurring even before we were born. Yet the body that is composed of living cells cannot be considered fully dead until all the cells have died off.
A possible answer could be: when the very last cell dies. That surely happens during the process of decomposition. It is worthwhile then to understand how cells die in general. Cells possess an enzyme family broadly called caspases which, when activated, carry out controlled demolition of the cell?s structural elements without causing stress to adjacent cells. How do caspases get activated? When a cell is under stress, mitochondria release a protein called cytochrome c through its outer membrane. Out of the mitochondria and inside the cytoplasmic pool of the cell, cytochrome c, which is otherwise integral to the basic function of energy currency generation inside mitochondria, activates the death director caspases that then do their job to perfection. This, in a nutshell, is how a cell undergoes programmed death. A very simplified depiction of a highly complex process.
The root cause of what makes the mitochondria release cytochrome c is still not fully understood. Many think that the stress is caused by production of reactive oxygen species (aka free radicals) generated because of excess electrons in the ATP manufacturing unit. We are talking of massive increase in free radical production. Because free radicals are regularly leaked by mitochondria and they act as signals to a number of normal cellular processes. It might start to look complicated now. The bottomline is that mitochondrion appears to be the key entity that decides not only how energetically the cell lives its life, but also the time when the cell must bid adieu to the world. Nick Lane reckons that it was ancient mitochondria that gave the caspase enzymes to our cells in the first place. Of course he means the genes that make the caspases.
If death is inevitable, what good could this be doing to nature or to life? Is death a means of gathering and reusing the building materials of life for a fresh build? Deciduous trees shed their leaves every autumn which enrich the soil for new growth to occur in spring. Animal carcasses become breeding grounds for maggots and provide nutrients to bacteria and soil. Yet this cannot be the main purpose of death. Why would nature bring down bigger houses to build/maintain smaller houses? It maybe that death in some cases helps bring resources to places where they normally don’t exist. I am thinking of Pacific salmon which start their lives at the source of a river, spend their youthful days in the ocean and, having matured there, begin an ultimate journey upstream to their birthplace to release eggs and sperms and die. That way they do bring nutrients available in ocean waters onto the land. They are genetically programmed to do this.
One idea is: death is all about discarding a life institution when it has served its main purpose – reproduction. Gerontologists use a term ‘essential lifespan’ to indicate the age when a species is supposed to have fulfilled the purpose of reproduction and beyond which it undergoes progressive loss of function and fitness. For?Homo sapiens, the essential lifespan is 45 years. Reproduction indeed is a precursor of death. Most animals die soon after losing their capability to reproduce. We humans, along with short-finned pilot whale and killer whale, are exceptions in that females live for decades after they stop producing eggs. Advances in medical sciences too have helped increase our longevity. This makes us live with the problems of old age that we see as diseases. Nick Lane considers old age diseases as mere symptoms and ageing as the real ‘disease’. Ageing has been attributed by various theorists to genetic programming and to wear and tear. Either or both of these could cause mitochondrial dysfunction leading to production of reactive oxygen species. This in turn results in damage to the DNA and eventually death. This is a convoluted and imperfect answer to the third question:?What is the root cause of death??There is a lot more to know and understand in this domain.
Yet again, we have come back to mitochondria while discussing death. Mitochondria do appear to take centre stage in most cellular processes including death. It would be interesting to find out what happens to mitochondria after cell death. What we know is that during cell death mitochondrial shape is transformed via fragmentation and cristae remodelling. These shape changes are being investigated for finding possible avenues for killing cancer cells. At cellular level, cancer is quite opposite to death although it is one of the common diseases that leads to death of an organism. Cancer happens when certain type of cells defy the death machinery and refuse to die. Mutations of mitochondrial genes have a lot to do with onset and spread of cancer.
The body, its processes and all the cells are destroyed as a result of death. The metaphorical old house demolishes itself after building a new house via reproduction. Across a generation, half of nuclear genes of each parent are inherited by an offspring. But what truly survives over generations is the mitochondrial DNA that a mother passes on to her children – like that friend who lives on beyond the bounds of life and death… “jibon moroner simana chharaye”?as Tagore puts it. Who knows, mitochondria could be the ones that make death die and that wake eternally as envisaged by John Donne centuries ago.
Lane, Nick (2005)?Power, Sex, Suicide: Mitochondria and the Meaning of Life.?Oxford University Press, Oxford.
Lane, Nick (2010)?Life Ascending: The Ten Great Inventions of Evolution?(Kindle Location 4363). Kindle Edition.
Wallace, D.C. (2012) Mitochondria and cancer.?Nature Reviews Cancer?12, 685-698.