Can science find out what happens after death

Researching Finiteness: Five Questions About Death

By what? The mechanics of death

Our biological death is inevitable. Because we are made up of billions of cells that age - until our entire body dies from them. About 300 different theories tried to explain exactly what "aging" means 30 years ago, while a generally accepted, coherent overall picture is still missing. At least two biological processes certainly play a role: the ticking of the "internal clock" and failing repair systems.

The former is the result of everyday cell division: It is important for growth, but also for the exchange of old cells that divide and are replaced by identical, completely renewed daughter cells. This process stops at some point - as if an internal clock had expired. Responsible for this is the gradual disappearance of the telomeres, which are a kind of biochemical protective cap at the ends of the chromosomes. Christoph Englert, geneticist at the Leibniz Institute for Aging Research in Jena, explains what happens: "When cells divide, the telomeres shorten because our enzyme and protein systems are not designed to replicate them completely. no more cell division takes place. " Without protective caps there are not only no more new cells, but the old cells either die or only live in "senescent" stand-by mode. The enzyme telomerase can counteract the internal cell clock, which repeatedly elongates the telomeres - but for good reason it is only active in a few cells. Because telomerase can promote cancer: "The shortening of the telomeres is also viewed as a so-called tumor suppressor mechanism: it prevents cells from degenerating because it limits the life span of cancer cells." Are we aging because otherwise we would die more often from cancer?

"If the telomeres become too short, cells no longer divide" (Christoph Englert)

This article is included in Spectrum - The Week, 12/2016

For every cell, age comes with wear and tear, for example through "oxidative stress", which can follow every breath: In the cell power plants - the mitochondria - electrons migrate to the inhaled oxygen, which ultimately creates energy and water. Rarely, but inevitably, are extremely reactive oxygen radicals. They damage their environment if the cell's own repair systems do not clean up in time - the cell ages. But we shouldn't demonize the radicals, warns Englert: "Experiments have shown that a slight activation of the oxygen radicals even extends life. This activates the cell's own defense systems, which then protect the cell from other stresses." Stress is therefore a double-edged sword: it first trains our defenses - but when it gets out of hand, it defeats us creeping and gradually. An Achilles heel of the cells could be the mitochondria, in which the oxygen radicals often occur. And indeed, explains Englert, "experiments show with Caenorhabditis elegans - a roundworm and popular model system in aging research - that the artificial inhibition of mitochondrial activity can have a life-prolonging effect. How we should classify the result in research is honestly still unclear at the moment. "

Our decay in old age is ultimately caused by several, not a single mechanism - and it is often the failure of several organs or biological processes that ultimately seals the end. The "entry gates of death" are predestined for this: the cardiovascular system, the lungs and the brain. All in all, their standstill reliably ensures that we are over after around 120 years. According to the expert Englert, this maximum life expectancy has not changed for thousands of years. The average life expectancy, on the other hand, is increasing - due to better living and hygienic conditions - in Germany by around three months every year. A trend that has been unbroken for 150 years.

When is the end? Attempts at a definition

To speak of "the" one death is too imprecise for medical professionals, which is why they have several definitions. "Clinical death" occurs when the cardiovascular system stalls and organs are no longer supplied with oxygen and nutrients. There may be a return from this death through resuscitation - thanks to medical advances in the form of ventilators or skillful chest compressions. The situation is different with "irreversible brain dysfunction", better known as brain death. In Germany it is defined as the failure of the cerebrum, the cerebellum and the brain stem and thus as the irreversible loss of what we call consciousness. Brain death does not necessarily mean that there are no more cells living in the brain: outside of the aforementioned brain regions, brain cells may still be active in deeper layers that are not recorded by an EEG.

The concept of brain death is controversial because important functions of the "brain-dead" body can be maintained using machines: it can continue to fight infections, regulate its body temperature or - in some cases of pregnant, brain-dead women - even carry babies until they are born. The body of some brain-dead patients still reacts to external stimuli, for example during an operation: the blood pressure rises, stress hormones are released or, the "Lazarus phenomenon", muscle movements are triggered. However, doctors only attribute this to reflexes of the spinal cord and not to the sensation of pain. Because brain death is very different from coma or the vegetative state. People whose brain functions are restricted but not failed are also in a coma; and comatose people usually breathe on their own. This also applies to patients in a vegetative state, the "vegetative state". The eyes of such patients are open, their brain stem works - but their cerebrum is usually damaged.