What causes people to die of old age? Do they literally just stop or is there a chemical reason?

Question: What causes people to die of old age? Do they literally just stop or is there a chemical reason?
- Keywords:
  aging,
  death,
  die,
  human,
  old age,
  people
Asked by butters to Amy, Drew, Julia, Kimberley, Sara on 16 Jun 2011. This question was also asked by nomnomnom, codycrowne13, caitlink0406, hamster.
- Drew Rae answered on 14 Jun 2011:
  
  Butters – We don’t know what causes old age, but we do know the effects of old age. They include weaker bones and muscles, and great susceptibility to disease. Ultimately all death is because the heart stops and the brain stem stops functioning, but in elderly patients there is usually some identified proximate cause such as infection, artery walls failing, or artery blood flow stopping for some reason. Not so much a chemical reason as a physical reason. The chemistry is just that once the heart stops beating, the cells don’t get oxygen and die.
- Amy MacQueen answered on 14 Jun 2011:
  
  Hey Butters,
  
  Everything in the universe tends towards decay (at least as I understand it?) – stars are dying, the sun is burning out, people get old and die, water carves away at the cliffs until they crumble…and your room gets messy. Its sad but its true – everything is going to end!
  
  One of the main causes of death these days is cancer which is caused by mutations in our DNA that make our cells behave abnormally…in the past it was more due to poorer diets leading to weaker bodies or bad sanitation leading to more widespread infectious illness. But even if we are really healthy we can only hope to live longer, not forever, eventually our bodies just wear out – and it can be for many reasons.
- Julia Griffen answered on 14 Jun 2011:
  
  Hey Butters (is that a southpark ref.) another good question.
  We age because our cells get less efficient. Our cells are being replaced all the time with new one. As we age this process becomes less efficeint, and errors occur.
  
  Basically we start aging once we stop growing… scary thought!
- Sara Imari Walker answered on 16 Jun 2011:
  
  Hello butters! Interesting question. I think the others have covered what happens to our bodies as we age. But something I think is cool to think about is why to multicellular organisms die at all? Think about bacteria for a minute. In some sense they are immortal they just keep on dividing. Sure they can die of disease or starvation, but they will never die of old age. That’s an important distinction, especially when we look at multicellular life. What blows my mind is something written on by Ursula Goodenaugh – she says that multicellular life is mortal most likely because of all the specialization our cells do. Once all these specialized cells do their thing so we can reproduce, they eventually die. So the very thing that makes us us -our complexity in all of the amazing cells that we are! – is also what makes us age and die. This just blows my mind!
- Kimberley Bryon answered on 16 Jun 2011:
  
  As far as I understand it people “wear out” from old age. The cells in your body are capable of diving and renewing themselves. For example, the lifespan of a tastebud on your tongue is about 10 days before it is renewed. However, cells have a finite ability to divide and once this has happened they can no longer renew. When this happens you can’t repair any damage to your body as well as when you were younger.
  
  As Drew said, in old people a minor infection can often kill an older person because their immune system doesn’t work as well as younger people.