# To what extent are you made of replacement parts? **URL:** \ **Category:** Factual Questions\ **Created:** [April 21, 2008, 9:57pm UTC](https://boards.straightdope.com/t/to-what-extent-are-you-made-of-replacement-parts/446315 "2008-04-21T21:57:29Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![sweeteviljesus](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@sweeteviljesus](https://boards.straightdope.com/u/sweeteviljesus)\ **Post date:** [April 21, 2008, 9:57pm UTC](https://boards.straightdope.com/t/to-what-extent-are-you-made-of-replacement-parts/446315/1 "2008-04-21T21:57:29Z")
There probably isn’t a really good answer to this since when a cell divides it is impossible to say which cell is the original, but to what extent has your body replaced your cells by the time you have reached adulthood? IOW, I expect that the skin I had when I was 10 has long since flaked off and been replaced by new tissue. To what extent is this true for other organs, especially the central nervous system? Thanks, Rob ---
**Author:** ![Waenara](https://avatars.discourse-cdn.com/v4/letter/w/50afbb/32.png) [@Waenara](https://boards.straightdope.com/u/Waenara)\ **Post date:** [April 21, 2008, 10:22pm UTC](https://boards.straightdope.com/t/to-what-extent-are-you-made-of-replacement-parts/446315/2 "2008-04-21T22:22:24Z")
I can’t even begin to answer this question myself, but I was curious and did a little googling. I found a few hits with keywords like atom, cell, turnover, and human. I don’t know how accurate this information is, but maybe it’s a starting point. [Atomic Tune-Up: How the Body Rejuvenates Itself](http://www.npr.org/templates/story/story.php?storyId=11893583): > [@](#): > > For most people, a makeover means losing weight and getting new clothes, hair and makeup. > > But what they may not know is that the body does its own extreme makeover regularly. In fact, 98 percent of the atoms in the body are replaced yearly. > > Researchers in the 1950s made the discovery by feeding their subjects radioactive atoms. Using radiation detectors, the researchers watched the atoms move all over the body. They found that the new atoms replaced old ones and ended up in all tissues of the human body. [Re: How many cells does a human lose every second?](http://www.madsci.org/posts/archives/2001-02/981770369.An.r.html): > [@](#): > > The atoms in your body go through a complete turnover about once every seven years. As with the loss of RBCs, this does not mean that your body is rebuilt miraculously on your 7th, 14th, 21s, 28th, etc. birthdays. Rather at any given time, most if not all the atoms that were in your body seven years ago will have been lost through metabolic turnover. ---
**Author:** ![Waenara](https://avatars.discourse-cdn.com/v4/letter/w/50afbb/32.png) [@Waenara](https://boards.straightdope.com/u/Waenara)\ **Post date:** [April 21, 2008, 10:28pm UTC](https://boards.straightdope.com/t/to-what-extent-are-you-made-of-replacement-parts/446315/3 "2008-04-21T22:28:22Z")
I’ve done a little more searching and I found a WikiAnswers that addresses this question: [Does the human body regenerate every 7 years?](http://wiki.answers.com/Q/Does_the_human_body_regenerate_every_7_years), and it references a newer study that found: > [@](#): > > They found the average age of intestinal tissue to be about 11 years, and after accounting for epithelial cells (which have short lifespans of only 5 days) found the average age of non-epithelial intestinal tissue to be 15.9 years. Skeletal muscle tissue was found to have an average age of 15.1 years. In the brain, tissues appear to be much older. The average age of the cerebellum’s gray-matter was only 2.9 years younger than the person, and the average age of occipital-cortex gray matter was about 10 years younger than the person, but the age of occipital-cortex neurons was found to be the same as the age of the person. > > So, even though we think of our bodies as being permanent structures, most of our tissues (outside of our brains) are continually being turned over, renewed in a balance between the constant death of old cells (likely through the process of apoptosis) and the constant birth of new cells. In last week’s New York Times article about this paper, Dr. Frisen (the senior author) suggested that the average age of the cells in an adult human may be as low as seven to ten years. Remember, this is an average value. As shown by Spalding et al, the value varies by tissue. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [April 21, 2008, 10:32pm UTC](https://boards.straightdope.com/t/to-what-extent-are-you-made-of-replacement-parts/446315/4 "2008-04-21T22:32:36Z")
I posted a question a few weeks ago about why tattoos are permanent, if skin cells get replaced. This thread just makes the question even questionier. ---
**Author:** ![sweeteviljesus](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@sweeteviljesus](https://boards.straightdope.com/u/sweeteviljesus)\ **Post date:** [April 21, 2008, 10:35pm UTC](https://boards.straightdope.com/t/to-what-extent-are-you-made-of-replacement-parts/446315/5 "2008-04-21T22:35:33Z")
How can brain cells live so long? Thanks, Rob ---
**Author:** ![Bob55](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@Bob55](https://boards.straightdope.com/u/Bob55)\ **Post date:** [April 22, 2008, 1:29am UTC](https://boards.straightdope.com/t/to-what-extent-are-you-made-of-replacement-parts/446315/6 "2008-04-22T01:29:02Z")
I don’t think neurons die, they just replace their atoms. And as for tatoos - maybe they dye the cells that are actually doing the dividing? I’ll guess that since those cells shouldn’t die, the ink probably can’t leave the cells. Or maybe it stains the connective tissue and cannot leave that area.