According to Cleveland Clinic, organ donation is the process of removing an organ from one person and surgically placing it in another person. Most commonly transferred organs are the kidney, pancreas, heart and lungs.
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They age according to the age of the donor. There’s a lot of factors in what causes aging, but the upshot is that the organ will have experienced all of those withing the donor’s body first – the cell damage due to alcohol, crap food, lack of exercise, age – and the donated part will continue to age from the time of donation.
However, other than normal cell aging caused by, well, age, the new body will determine how fast the new part ages. So if well taken care of once implanted in the new host, it will basically age at the rate of the recipient.
So, for example: a thirty year-old alcoholic is killed by a freak accident involving projectile waffles. How it happened doesn’t matter, know only that it was batter up and the only salvagable part is the liver. Now, that liver had been soaked in alcohol, dude lived on fried bread, so it was aging fast: 1 year of age per year + 1/2 year of age to abuse, so from an aging standpoint, it was 30-years old + 15 years of abuse and damage = functionally 45 year old liver.
Now the new body it finds itself in is 25-years old, loves and cherishes that liver. It takes that liver and coddles it with clean water, veg, and a two kilometer walk every day with a dog that loves them and the world it lives in. Like, seriously, that dog is awesome and great for mental health. So the new liver continues to live one year of age per year, and no added stress and abuse, so it ages normally. The 25-year old body has a 45-year old liver, but it will continue to age normally and now that it’s being treated better, might even last a little longer than expected.
I haven’t seen anyone mention the fact that once inside the recipient the donated organ will be under constant attack from the recipients immune system, which will prematurely age the organ. Because of this transplant recipients take immunosuppressive drugs to reduce the amount of damage their own immune system will do to the new organ. It’s a balancing act between suppressing the immune system enough to stave off rejection of the new organ (which is almost always inevitable) and having enough of an immune system to fight off basic infections. This is why it can be difficult to find a match when looking for an organ. The closer the new organ is to the recipients own genetic markers the better.
So there’s this thing called the Hayflick Limit, and its important. Every time (most of) your cells divide they lose a little bit of DNA. At first the DNA being lost is useless stuff off the end, but eventually they will start losing useful DNA. The number of times they can divide without losing real DNA is the Hayflick limit, and for a human the number is 50ish. Cells can divide about 50 times before they start losing DNA that is valuable (and thereby rapidly declining).
So let’s say you are getting a new kidney from someone who was 70 years old. Just by being that old, they’ve probably burned through a lot of those cellular divisions over the years. We can put that kidney in a 25 year old, but that won’t add any DNA back to the kidney cells that it lost through normal division.
And so when people talk about being hard on your body, it usually boils down to killing off cells and forcing them to divide to replace themselves – effectively accelerating their aging. Do you box and take a lot of punches to the kidneys? That’s going to force those kidneys to repair the damage via cellular division, and those are a finite resource. When people start breaking down of old age what basically happens is the number of cells that are able to have continued healthy divisions is starting to become scarce, so the organs are having a hard time maintaining themselves.
And all of this Hayflick limit stuff may sound bad, but it basically makes you immune to cancer while it is working (for cancer to develop a mutation to remove this natural limitation must occur). So it guarantees you will die some day due to aging, but it makes it much less likely to be from cancer at an extremely early age.