All New Cells Every Seven (Nine?) Years?

[Wally]

Greetings!

I have read/heard from various sources that none of the cells in my (or any other human's) body now are the same as they were seven (At least one source said nine years) years ago. I remember reading from one source that some cells don't "die" but all of the separate parts are replaced, so that the entire cell really is different, without having died.

I remember being told that some memory cells are never replaced, and some brain cells are replaced after fifty years. Would they have changed all of their parts without dying, as mentioned above, in essence making them new cells?

Am I a completely different person than I was less than a decade ago on the cellular scale? Thanks in advance.

 

[Another God]

Good question. I am pretty sure that the "you are a completely different person every 7 years" is just a colloquial exageration which is picking up on the average lifespan of our bodies cells. It is true that some cells are never replaced, like the brain cells, while cells in the stomach lining are replaced very very regularly (due to the extreme conditions).

So I would guess that you are, by mass of turned over cells, a completely new person. But in reality you have some consistent cells which never die, and some which are replaced regularly, so no, you maintain a constant part of yourself for most if not all of your life.

(as an educated guess)

 

[Wally]

Thank you for replying!

In Bill Bryson's A Short History of Nearly Everything (Page 373 of the hardcover edition, Part V "Life Itself", 24 "Cells") he says: "Brain cells last as long as you do. You are issued a hundred billion or so at birth, and that is all you are ever going to get. ... The good news is that the individual components of your brain cells are constantly renewed so that, as with the liver cells, no part of them is actually likely to be more than about a month old. Indeed, it has been suggested that there isn't a single bit of any of us - not so much as a stray molecule - that was part of us nine years ago."

Is it true that "the individual components of your brain cells are constantly renewed", and all other cells?

 

[Another God]

Well that does also make a lot of sense. Virtually every part of the cell is an equilibrium of sorts, with things being broken down, new copies being recreated and the rate of the two being the determining factor for how much is present.

I've never really thought about that part of that claim.

But since it is an equilibriated system, it would be like pouring fresh water into a bucket full of dirty water. Eventually it would look like a clean bucket of water, but there will always be the smallest percentage of dirty water in there.