I’m fairly certain that, at the base level, we die when our body (or critical parts, such as the brain or heart) is deprived of oxygen. Of course, I could be wrong. If I’m right, then that would explain what causes us to die when we have a heart attack or a stroke or we are shot in the head.
But with other diseases that result in death, such as cancer, Parkinson’s, Alzheimer’s, etc., it isn’t clear to me what the mechanism is that causes us to die.
So, what is it that kills us? Is it ultimately the same mechanisms, regardless of the disease?
I think that senescence is the copying of the DNA to create new cells is like photocopying a file format that is subject to lossy compression. As the DNA is copies the replica is more subject to corruption until finally the DNA is so corrupt that it can no longer function in its role of replicating itself.
In the cases of the particular pathologies you are referring to that’s pretty simple, yes it’s a lack of blood flow. Not just oxygen but nutrients in general. Parkinson’s I believe is a degeneration of the basal ganglia. From Wikipedia
So no in the case of Parkinson’s and Alzheimer’s it’s a degeneration of neurological tissue that is not related to some kind of hypoxia as it is with the pathologies you mentioned in the first paragraph.
But how does degeneration of the basal ganglia or other neurological tissue result in death? Is it that the lack of any neurological tissue to direct the heart to pump that leads to the death?
That’s completely not true, I’m afraid. It’s a nice metaphor, but totally wrong. Telomeres shorten, as dozens of people will inevitably mention here in a minute, but accumulation of errors isn’t a major issue. Look at it this way - all of your DNA has been copied from your parents’ DNA, which was copied from their parents’ DNA, which was copied from their parents’ DNA, etc, etc. If copying was really that sloppy, we’d have been extinct long ago.
As for the OP’s question, I’ll leave it to the real medical professionals, though I will point out that it’s been covered here before.
I think you are conflating “What kills us?” with “What is a definition of death?”
Let’s start with a definition of death: We are dead when enough of the brain is irreversibly non-functional to meet someone’s criteria for “brain-dead.” The specifics are the subject of great controversy when the brain dies in pieces, which it often does. Are we dead, for instance, when the part of the brain that is our consciousness is no longer functioning? We can use tests like brain scans and EEGs to try and figure out how much brain is working, but unfortunately some folks–most of us, maybe–die a few cells at a time so it can be a pretty grey line. I sometimes use the analogy of looking at a city at night. Cut the power to the whole grid: the city is brain dead. Turn out a single 25 watt bulb: a single neuron just died–no one even notices. Turn off the power to a block: a small stroke. Make it city hall: a small stroke but unfortunately to a key area. You get the idea. At some point the city can be considered dead even if a flashlight is puttering somewhere, but it’s not always an easy thing to define.
Why do we die? Some primary brain disorders literally work themselves through the brain, destroying the brain itself a bit at a time. However many of them such as you mentioned–Parkinson’s and cancer–usually kill us from weakening the rest of the organism which can then not sustain a proper blood flow to the brain. Perhaps there is dehydration; perhaps a secondary chemical abnormality–things like that. Often a weakened body can’t fight off infection so the terminal event might be something simple like a urinary tract infection that got out of control and invaded the whole body. The underlying reason for the weakened immune system was the disease itself, but the secondary illness causing the patient’s death was an infection. It is often said in medicine that pneumonia is the friend of the aged (the idea being that most of us don’t want to continue indefinitely with otherwise compromised brain and physical function).
I guess you might say the actual terminal event for a given cell is that it no longer can be supplied with nutrients and have its metabolic waste carried away. That’s essentially a function of proper blood flow.
That’s not how I read mswas’s statement. I think there is a great deal of difference between copying of DNA from generation to generation and copying of DNA within a generation. Surely one’s DNA is not as robust at the age of 90. Perhaps one of our many professionals can elaborate
Nope. We die when there is no longer any any voltage difference between the inside and the outside of the neurons in your brain. In simple terms you’re dead when the electrical batteries in your brain goes flat.
That can happen when your brain is deprived of oxygen, but it can also happen in situations such as poisoning or being disintegrated in an explosion where your brain actually has access to more oxygen than it normally has.
Insofar as death is defined as brain death, and brain death is defined as alack of electrical activity in the higher brain centres, then yes, its’ the same mechanism.
Nope. The heart has an intrinsic pacemaker and it will pump along just fine without any neuronal input.
Heart failure can be caused because neuronal input disrupts the internal rhythm and causes the heart to pump too strongly or too weakly, leading the heart itself to fail. Or it can be caused because the disruption of neuronal input fails to adjust heart rate adequately for the body’s demands.
Parkinson’s death is usually caused by a failure of other (muscular) body systems, enabled by the failing brain. For example, improper swallowing leading to choking to death, or to aspirating food into your lungs, which then leads to pneumonia, which leads to death. Or maybe something as simple as uncoordination leading to a fall, which causes massive brain injury, or causes broken bones that lead to long hospital stays, where the patient picks up a secondary infection (such as pneumonia…).
I am unaware of any data showing that our DNA repair mechanisms degenerate as we age. That said, it wouldn’t surprise me that some degeneration occurs. I am much, much more skeptical of the claim that less efficient repair contributes significantly to death mechanisms.
Is cancer not sometimes caused by genetic mutations? Is DNA not genetic material? Certainly some forms of cancer are more prevalent amongst the aging population, I cannot imagine it’s mere coincidence that they are A) older and B) have certain forms of cancer that are more prevalent amongst the older population.
A professional’s insight would be highly welcomed.
Absolutely. Cancer is often caused by accumulated DNA damage (NB - damage of existing DNA is a very different thing than errors occurring during replication), and that’s an important thing. What I am arguing against specifically are mswas’s assertions, or implications, that
A - DNA replication becomes more error-prone as we age. At the least, I’d like to see a citation for that.
B - this increase in DNA replication errors is somehow significantly responsible for our aging and dying.
I don’t know if you’d consider me a “professional”, but I spent six years working in a medical genetics lab, and am now working on a PhD in biology focusing on fruit fly molecular biology and evolution. Just for the record.
I was trying to answer the question in the context of the OP.
But sure; a guy next to an atom bomb doesn’t have poor blood supply as his proximate cause of death.
I’m not one of those professionals, but AFAIK, elderly men can father healthy, defect-free children. One might safely conclude that their sperm, which have been produced within the few months prior to conception of their child, are carrying healthy, defect-free DNA.
There’s been a whole bunch of research in the news lately about how certain birth defects become more likely with the increasing age of the father. It seems reasonable to conclude that there is some degradation of sperm DNA. And this damage seems to start in the 40’s.
