Does the human body really replace all its cells within the span of seven years? This is a “fact” that I hear tossed around a lot, but I’m not sure if this is just a myth. Citations would be helpful.
Could not find a reference addressing the question specifically. Once adulthood is reached cell replacement/repair is an ongoing process.
With advancing age it apparently slows down and/or is not as efficient.
An MD may drop in shortly with references and more complete information.
Not true. Brain cells can live a lifetime (in fact, until recently, it was also a “fact” that brain cells are not regenerated).
Cite: http://www.usatoday.com/tech/columnist/aprilholladay/2004-08-13-wonderquest2_x.htm
Is it true that the subatomic particles that make up those cells are completely replaced on a time scale that makes seven years seem like an eternity? Or can we hold onto our protons long enough to feel attached to them?
Larry, nope. The lifetime of a proton is at least 10^35 years (wikipedia). To compare, the age of the universe is about 10^10 years (wikipedia).
Whether the protons that exist in your body have been swapped out through chemical processes is another question.
Not talking about decay of a proton or chemical processes.
New-agey folks like to invoke quantum mechanics and say that all that the permanence of the physical universe (such as it is) is illusion, because all that remains is the pattern - the subatomic particles are constantly flying off and being exchanged with the stuff of all the matter around us, at the speed of light.
Now, I know approximately squat about particle physics, but I suspect that the folks who like to make this assertion have most frequently have an even more vague understanding of what’s going on.
I know that it’s at least partially true, in that there are particles being exchanged between “solid” bodies, and there’s that whole “field” thing going on when you really squint at things.
My question is whether or not there are any relatively sedentary subatomic particles. I’m wondering how long a quark is likely to hang about contributing the whole business of Mudd’s atomic structure before it gets distracted and decides to make the jump from my ass to my desk chair to contribute to the existence of a proton that’s playing at being part of iron atom in one of its screws.
I know (or at least think I know) that electrons are pretty damned restless and hop all over the damned place, but I don’t know if the hadrons that form a proton in an iron molecule are the same little buggers until the iron molecule is no more, or even if the molecule keeps the same proton throughout it’s entire existence.
My intuition would be that it’s just the particles that make up EMF fields that are so freely exchanged and some particles remain constant, and that the new-agey folks are making their conclusion based on an incomplete picture – but I don’t really expect that what’s happening on the subatomic level to be in any way intuitive.
Just pretend I previewed that. I hope y’all can still parse it in spite of the few misplaced words that are stuck in there.
Myth. Diiferent tissues are replaced at different frequencies (the exact rate depends on age - younger indiviuals cycle faster), but some tissues are remodeled very slowly if at all. The lining of the small intestine turns over every 4-6 days. The outer layer of skin turns over every 4-6 weeks. The mineral portions of bones are replaced at a rate of about 10% per year. On the other hand, when you die the majority of neurons and corneal cells in your body will have been there when you were born.
In terms of cellular components, cells continually renew and replace their lipids (fats) and proteins (again, rates vary by cell type and age), but the DNA of non-dividing cells will persist without renewal for decades, even the entire life of the organism.
JRB
Sorry to ask, but do you have a citation for this?
Normal red blood cells last about 120 days in the bloodstream and then die.
There is constant turnover, of course.
so… that would fit in with the idea that within the span of 7 years you’d have all new cells. I’m not asking about whether it’s EXACTLY seven years, I’m asking whether all your cells will be different 7 years after any particular point in time.
Oh, lordy. Okay.
Quarks are well known for ‘never leaving the house’… it’s in fact their defining characteristic - the house, in this case, being the hadron particle that they make up. Protons and neutrons are hadrons, as well as some more exotic particles that are harder to come by. We theorize the existence of quarks only because it’s the most sensible way to explain the way hadrons behave that they are put together out of these smaller building blocks. IIRC, there is some evidence that the further apart you pull quarks making up a hadron, the stronger the forces pulling them together grow, and so you can never truly seperate them. The fact that they’re always stuck together is called ‘the property of confinement’ apparently.
Hadrons also generally stay put inside atomic nuclei… except for events like radioactive decay, radioactivity absorption, nuclear fission, and nuclear fusion. Now, a certain small amount of this does go on all the time - that’s the source of background radiation. Atoms inside your body are decaying right now… probably some carbon-14 and maybe a few more exotic isotopes. But compared with the number of atomic nuclei which are remaining stable, the ones that are atomically active make up an exceedingly small percentage.
On the chemical level, though, atoms switching between molecules, forming new molecules, breaking up existing molecules, etcetera, this is one level on which human bodies, in fact most living creatures, are boiling soups of frenetic activity. So to answer your question… we can’t really hold onto our protons very long because we lose the atoms and molecules that they’re attached to. Otherwise, yeah, they’d stick around a long time.
I hope that this helps.
It helps enormously, chrisk. Thanks very much.
I’ve often heard new-agey types assert that, from breath to breath, every single subatomic particle that previously made up your body is light-seconds away and off in search of new horizons.
I suspected that it was a load of dogs’ bollocks, and I’m grateful to have my suspicion confirmed.
I am not sure I am following the question. People already explained that there is different turnover for different organs and many billions of brain cells will be with you for life. The brain is fairly important so I am pretty sure that alone rules out the complete turnover in 7 years statement.
Er, which bit? I’ll give a few references here, but if you have a particular point in mind I’ll see if I can dig up more.
I tried to find articles that fulfilled these four criteria:
- Has actual numbers
- In a well-respected journal (which generally mean they are more likely to be written by someone who knows what they are talking about)
- Not so technical as to be incomprehensible to non-specialists (although since all of my friends are also biologists my perspective on this may be somewhat warped)
- Freely available - I’m assuming you are merely an interested bystander and not willing to subscribe or go back to school to get access…
Eventually I gave up and compromised, especially on point 2. You’d be surprised how little good biology research is freely available (although this is showing signs of changing).
Most of the following are reviews (summaries and discussions of many different bits of research). They are also mainly older, since older articles are more likely to be free. If you like, I can also link to some primary articles, which are generally much more technical, and most of which require subscription (or institutional affiliation) to access the article, although you can read the abstracts free.
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Chapter 3 of “Rook’s Textbook of Dermatology” gives an estimate of the skin epithelial turnover time on page 3.14.
Chapter 3 is a free sample from the book. -
More than you will ever want to know about turnover of the gut lining (and many other things about it):
Karam, SM. 1999. Lineage commitment and maturation of epithelial cells in the gut. Frontiers in Biosciences. 4:D286-98. (PubMed doesn’t annotate this as free, but I was able to download it without signing in…) -
A review which gives various estimates of bone resorption, but without telling where he got the numbers:
Watts, N.B. 1999. Clinical utility of biochemical markers of bone remodeling. Clinical Chemistry. 45(8 Pt 2):1359-68. -
The cornea is actually a bit more complex than I originally implied. There are two cell layers, the epithelium (outside), which does turn over (fairly quickly, in fact), and the endothelium (inside), which doesn’t (or maybe does but very slowly). There’s a few throwaway sentences on both (with cites) in the Introduction section of this article (I couldn’t find anything better that was freely accessible):
Faragher, R.G., et alia. 1997. Aging and the cornea. British Journal of Ophthalmology. 81(10):814-7. -
Neurons: the literature is unfortunately not very layman-friendly.
The February 2002 issue of “The Journal of Neuroscience” has an entire cluster of freely-available mini-reviews on the formation of new neurons.
This is a very thorough but probably incomprehensible recent review:
Abrous, D.N., et alia. 2005. Adult Neurogenesis: From Precursors to Network and Physiology. Physiological Reviews. 85: 523-569.
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Lipid and protein turnover: I’m begging off on this for the moment. This guy seems to have some legitimate citations, although I tend to be leery of anything with “Nano” in the title.
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DNA stability in non-dividing cells: my favorite paper is this one. It’s a dinosaur, and not available online (although you can read the abstract here), but I love it because the premise is just so goofy:
Slatkin, D.N., et alia. 1985. The stability of DNA in human cerebellar neurons. Science. 228(4702):1002-4.
I hope you find this helpful,
JRB
Aw, c’mon. Ashton Kutcher says it’s true, so it must be true.
Super bonus points to whomever knows where he said that and in what context.