Selects: Does the body replace itself?

Hey, everybody, it's your old pal Josh for this week's select. I've chosen Does the body replace itself every seven years? Sounds like a medical episode, and it kind of is. But after a little while it turns into a brainbuster of a head scratcher of a philosophical bent that I think you're gonna love. I hope you enjoy the living.

Heck out of it.

Welcome to Stuff you Should Know, a production of iHeartRadio.

Hey, and welcome to the podcast. I'm Josh Clark with Charles W. Chuck Bryant and guest producer.

Nol Knowle's in the house.

It's the it in the new studio. Yeah, man, this place is comfy, cozy. I like it.

I wish I'm I don't know, I wish there was a chair version of a waterbed.

I know this is a napish little place.

Yeah, especially today, I think I'm dragging all apologies.

Yeah, same here. So if we're talking kind of slow or low, or we just stopped talking for a little while, it's we're as tired.

Yeah, bumped into you at the Hawks game last night.

I know, Hey, how many is that?

You know? Yeah, just at the bump in yep.

We were both at the Hawks gaming and the Hawks.

One didn't even know we were going. Look over in line, there's Josh and Yumi. Yeah that's great. There's Chuck and Eddie. Yep in an arena of eighteen thousand bumping into someone?

Is that it?

That's all it holds?

I think it's something like that. It's a good lot of people.

It's a good arena.

Yeah. But you had box seats because you're special.

They were free out.

Mine were free to in. The nose bleeds.

I liked just about every seat in that place.

Yeah, it's not too bad. I was.

I was laughing about the nosebleeds going in, But then I got up there.

I was like, this is great. Yeah you can see everything.

Did you nose actually bleed just twice?

Yeah, once out of its sheer excitement and then once from the altitude and that was more of a spray, rightah yeah.

Just covering everyone that was like go Hawks.

Boy, what a weird intro.

It's a little weird, but I mean it kind of jibes a little bit because we're talking. Yeah you're mentioning blood.

Sure, it was shedding cells and blood.

You were like, blood is made up of cells and we shed tons of cells. But before we get to that, right, there's the fact that the podcast you shed cells. I want to mention this one thing I read. Yeah, it's called I think the title of the article is the Self is Moral. It's about like where we get our identity of self from, like where it's rooted. It was written by a person named Nina Stromyer. I believe it was on AON magazine. Yeah, just type in the self is Moral aon it'll come up.

I'll get you there.

Uh. And towards the beginning, the author says, there's this very famous philosophical exercise, which you know, philosophers love to do, like mental exercises.

Yeah, that's what that's all they hashened.

So imagine you have like a kind of imagine you have like a ship, right, like a boat. Yeah, a nice Yankee clipper, okay, okay. And this Yankee clipper is slowly, over time kind of salvage for parts. But rather than just being stripped, like every time a part is taken out, it's replaced, and then over the course of like fifty one hundred years, is each plank, as each bolt, as each like mast head, even the thing. The carved lady in front eventually just gets replaced with something else.

Yeah, a new carved lady that speaks of the time.

Right, you know? Is it still though, after every single part has been replaced, the same ship that it was before?

Yeah? I see what you mean. I don't think that can be possible.

Why not, especially if it has the same name and it's the same ship in the same place as before. It was just slowly, over time moved out. True, where does the self lie?

Yeah, that's a good point, man, Like redoing a house, same thing, Yeah, I mean, like they saw the floors and the walls and the windows, Like, when does it cease to become that same house that was built in nineteen thirty exactly.

Isn't that cool?

Yeah? It is really cool.

And the reason that it applies to this episode is because, over the course of your lifetime, a significant portion, pretty much all of the cells in your body are going to be replaced. Yeah, so that the person even after you reach your adult self. Yeah, physically, by the time you die, assuming you're gonna die much later, you are essentially a different person, at least on the cellular level.

Yeah, thirty seven trillion cells.

Ish that's how many we have.

Yeah, that's what they estimate. And I did a little looking into.

Lifespans, like an estimate.

Thirty seven trillion. Yeah, what do you want like to like give or take?

Yeah, I did a little research into lifespans just because this all sort of comes back to like your death basically, because that's all death is, is your your cells, you know, dying little by little.

Well yeah, I mean if you think about it, Chuck, one of the things that.

Like why do we die?

If our we'll get to all that, Oh okay, but it's intriguing, you know it is it started, you know, questions started popping up. So apparently we gained about three months every three months of life humanity every year that we progress.

Like the average life span spans by three months.

Yeah, Like if you were born in twenty twelve, the average lifespan is now and this is the United States, is seventy eight point eight. If you were born in nineteen oh one, it was about forty seven and fifty years for men and women respectively. But if you look at the ratio, it's still about three months. Despite all our technologies, three months a year, every year, every year.

Just slowly creeping along.

Yeah, because I think the article it was like when we're going to live to be one hundred by average, and they say by the year twenty one hundred, if things hold, then the average human or American will be about one hundred years old.

I thought that, so I guess that will if things are steadily progressing. I had heard that like our generation would be either the last or the first, the last to not hit triple digits or the first two on average. Yeah.

Yeah, I guess these are all gases, you know, so who knows. Plus if you believe in like things speeding science, speeding up?

Yeah, what is that? Moore's law?

Yeah? Is that it? Yeah, applied to computers, so in that case.

Right, right, but I mean you cantend it other stuff.

Yeah, then you might think, you know it's it's but you know, they say it's not increasing like that.

No, at least not so far.

Moore's law is exponential growth just adding three months every year's yeah, non exponentials geometric. I think we're still at non exponential growth definitely. Yeah, we're just adding three months. Yeah, it's not bad though, that's pretty good average every four years.

It's an extra year, yeah, well, and it's interesting to think about. You know, people that were born you know, a lot of our colleagues like eight years behind us, are going to live an average of.

Two years longer.

Yeah, that seems unfair, sad.

Yeah, I know, what did they do to.

Observe that we're we're thinking about our own deaths today? Yeah, and chuck that there's this rumor theory, legend maybe okay, that your body regenerates itself ninety percent of your body regenerates itself every year.

Yeah that's not true.

No, it's not true, but it was a very long standing rumor, and it was actually based on science. Yeah, you know, not just the idea that, oh yeah, ourselves regenerate. So back of the envelope estimate is that, you know, we regenerate ninety five or ninety eight percent of ourselves every year. It was early experimentation by injecting radioactive isotopes into human beings, yeah, and then following their course and then making estimates based on that led to this idea.

It's called pulse labeling, is it. It's like tagging an animal in the wild basically.

Right, but you're just tagging a cell.

Yeah.

The specific types of cells.

Yeah, they don't do that to humans anymore. No, it's very animals. I think it's a very dumb thing to do.

Sure, injecting radiation exactly.

Yeah, unless, of course, you know it's radiation treatment that's true, which is still a really weird thing if you think about it.

It's Yeah. I have a feeling it's gonna be like one of the things we look back on.

As like a primitive treatment. Yeah, yeah, yeah, I hope so.

But there was this long standing science for decades or this idea, scientific idea that we regenerated ourselves by ninety five ninety eight percent. Finally, and I think two thousand and five there was a a researcher named doctor Jonas Friesen. He's Swedish.

Dude's awesome.

He said, this whole urban legend is really bringing me down. I want to figure out a way to really track how often the human body regenerates itself.

Yeah, and the biggest question has been the brain, specifically the cerebral cortex and the heart and the heart muscles. I mean, they want to know all this stuff, but those were the two biggest mysteries.

I think, right, there's still the mysteries, but if you went back to prior to two thousand and five, in doctor Friesan's research, it was all a mystery. Yeah, he figured out. He basically put a very act curate time stamp on how often human tissue and human cells regenerate themselves. Right, So the way he did this is very clever. For a long time, botanists knew that the trees around the world contained a spike of carbon fourteen radiation.

Yes, thanks to humans and nuclear bombs.

Exactly from nineteen fifty four to nineteen sixty three, tree rings for tree growth around the world show a big

We also eat plants exactly contain the sea fourteen besides breathing it in.

And we also eat the animals that eat the plants that in just see fourteen. Right, So like we got carbon fourteen in our bodies, that's right. But because of the spike in carbon fourteen that was introduced to the atmosphere from nuclear testing, there is a spike in humans as well. So you can roughly age like a human compared to another human if they were born in say nineteen fifty nine, and one who was born in nineteen seventy after there was that spike of carbon fourteen had

Yeah, he was He went looking for a marker, and he found one due to our atomic testing program, which is pretty weird. You just released all that junk in the atmosphere and now all these years later it has a nice use.

Yeah, you know it does.

So we now know when we're going to die, right sort of. And the reason he was able to use this as a marker, Chuckers, is that when you take a.

Breath of life, your first breath of life, that's right, and you get some you get some of that C fourteen into your DNA, and a steady amount stays in there, like you don't keep ingesting C fourteen as far as I understand, as far as your DNA goes, Oh okay, once it's in your DNA, as your cells divide, that original amount becomes divided evenly. So the less C fourteen that's in tissue, the older that cell line is. Where then the younger the actual cells are. Right, Is that right?

I think so, which would mean the new cell the marker would be a fresh batch of the C fourteen.

No, it have less C fourteen.

Oh really, yeah, let's say you have because the cell divided, yes, exactly, Yeah.

Like you have ten grams of C fourteen, which you don't. I can't imagine what that would be. Like. Let's say your your one cell that's never divided has ten Yeah, when it into two, it's each of those two cells is going to have five grand and then two and a half, and then one point seventy five and so on and so on. So since you know that C fourteen is generated at a constant rate, you know that it decays at a half life of fifty seven hundred and thirty years, you can look at the amount of

Was Yeah, he's a little like a bingo card. He just from the calendar that he made with the trees, and he holds it up in the light, and that's how he determines it.

It's not true.

But what he did determine though, was which is really cool, And this is sort of what we've been building toward, is that most of your cells are about seven to ten years old, yes, in the body, and there are variances, and of course we're going to talk about all that, and right after this break, we're going to give you a little primer on cells.

So you know what all this means.

Right, All right, Josh, were promised to sell primer, and we like to deliver on those promises.

Here stuff you should know.

So I guess we started off by saying there are thirty seven trillion cells about in the human body. Yeah, give or take, give or take, and water makes up about two thirds of.

The weight of those cells. Oh yeah, that's right. They're tiny.

You need a microscope to see them, and it's like it's the tiniest thing that can still reproduce.

Yeah.

And even though we have many different kinds of cells, I think two hundred types, and within those cells there are differences, but there are a lot of similarities with all cells in their structure. Namely, they have a cell membrane, they have a nucleus, have a nucleus, some have more than one. And these membranes are what allows nutrients to pass in and out, waste to pass out water through osmosis travels in reverse, osmosis travels out.

Yeah.

And what else, We got your mitochondria as well. That's where this is the important, really important thing, which is basically what keeps your cells alive.

That's the power center, right.

Yeah, and that's you know, your cells need food to live just like your body does. But you can't pass that that hamburger straight into your cell, right. It needs to be broken down so your cell can use.

It exactly into what adenosne triphosphate ATP is like the universal cell fuel, right.

Yeah.

So there's a lot of stuff that the body does make. I think you need like twenty three I think you need twenty three amino acids, and like nine of them your body doesn't really manufacture. So those are the nine non essential amino acids, right. And you use amino acids to build proteins, and use proteins for everything from making muscles, to making red blood cells to you're mounting and immune response.

Yeah.

So you go out and you find yourself a nice pig and you cut off its back leg. You say, sorry, pig, here's a pig leg for you. But I need this leg. I'm gonna eat this leg. And what I'm really eating is the muscle. What I'm really really eating is the glutamine. Yeah, and in my body's going to take this glutamine. It can make it itself. But it doesn't hurt to have an extra little bit of glutamine.

Yeah, it does to have that pig leg And you're exactly right.

So I'm chomping on the pig legs. The pigs must and listeners by the way, right, just use your imagination for a second. Sure, And yes, I'm sorry too. So you're eating the pig like and you're gaining this glutamine as a result, and your body's metabolizing the glutamine and then reusing it, right, And it can be glutamine, it

For better or worse, depending on what it is. Of course.

Yeah, that's a great I think that's ultimately one of the side lessons of this whole thing is we should take care of ourvironment because that environment becomes us and we either suffer or thrive as a result of it.

You ever heard the expression you are what you eat?

Exactly?

Know, you literally are what.

You eat, quite literally. And then also chuck, it goes the other way as well. When we excrete waste, when we exhale CO two that's taken up by other things in the environment, is deposited into the environment and it becomes part of the environment itself. So not only do we regenerate our cells, regenerate tissue on average seven to ten years, become almost wholly a new version of ourselves.

Yeah, we lose on average, they say nine the average adult male loses ninety six million cells per minute, But we also replace those at the rate of ninety six million per minute, yeah roughly.

Yeah. Yeah, so that's the good news.

So we've got all these cells that we're losing. We've got all these new cells that are replacing them. And I think, like you said earlier before the break, that these the different types of cells and then hence different tissues regenerate at a different rate, right.

Yeah, And they all have specialized jobs, and the cells are often built in such a way to aid that job physically, you know, different to make that job easier.

Which is really cool too, right, shows how versatile they are.

Yes, you know, like stem cells are very versatile.

Super.

So let's say your skin, Yeah, your skin regenerates every two to four weeks. I think, yeah, exactly, you get a new healthy coating of skin every two to four weeks because you're epithal cells are particularly good at regenerating themselves.

That's right, And that is well, I guess that would fall on the low side, obviously, if we're talking seven to ten years. On the super low side, you have the cells that line like you're intestine in your gut, and those things don't last long at all because it's such a harsh environment. You know, you wouldn't expect them to last like weeks and months and years.

I think, how long is it? Five days?

Yeah, that's nothing but the.

Structure of your guts that are beneath that membrane lining that turns over five days. They last about fifteen years.

Yeah, it's such a like a beautiful, elegant system. Yeah, that we have right to keep us alive. Red blood cells last about one hundred and twenty days. But then you have things like cells in your bone which actually regenerate as well, so your bones are over time, over a much longer period of time, actually becoming I mean, I hate to call them new bones, but they kind of are, you know.

Well, yeah, I mean compare if you took your femur and somehow compared it to your femur when you were fifteen years old, Like, they are two totally different bones. Even though they're your bones. They were in the same place, growing in the same person with the same DNA. There's still different bones because they're made of different cells. Ten years or so for the bones, yeah, something like that. For the human skeleton, three hundred to five hundred days.

It's pretty amazing, actually.

Yeah, because it will just grow right back, kind of like a hornet's nest.

Interestingly, the inner lens cells of your eye form and your embryo and basically don't change. Yeah, now, is that why you have suffered from degeneration and vision?

That's what I would guess.

Is that the reason?

Yes, so the reason so with the corneal lens, Chuck. When you're when you're born, when you're conceived, right, you are a cell of coross that divides. Finally, once that first division takes place, those corneal cells, they're set in stone. Like your corneal cells are as old as you are, same age as you. Other cells that make up different parts of the eyes they're far newer. But your corneal cells, your cerebral cortex cells, they think.

Yeah, that's the one I mentioned. The brain and the heart muscles, those are the two big ones. Because obviously the reason we have diseases like Alzheimer's and dementia are because the cerebral cortex has long a thought to not regenerate cells at all.

Yeah.

Now I think they believe that they do in a very small number.

Or different reasons, like the old factory bulb supposedly does. Yeah, in the hippocampus, so we can learn new things. Their sense of smell can be refined over time.

Yeah, And I think isn't that also the reason the smell is very much tied to your memory, probably like a smell can conjure up a memory more clearly. Yeah, but the cerebral quartets itself, they don't think.

Who was her name?

Elizabeth Gould of Princeton did a lot of work on this because it was just basically set in stone for years like, no, it doesn't happen. And she did a lot of work over the years trying to prove that it did using tracer studies. And I think that where they are now as they think it does.

Some yeah here there, here there.

But obviously we still have to mention Alzheimer, so it's not it doesn't regenerate like the rest of the body, not even close.

Yeah. Alzheimer's also maybe produced I guess by plaques and member plaque build up in between your neurons that keep them from firing as well.

Yeah, that's it seems like we're so close to figuring out the secret, you know. Yeah, to uh, I don't know about not dying ever. I'm not talking immortality, but living much longer lives.

Well, let's talk about that because all of this stuff kind of leads to that question, if we regenerate so often, why do we die? And we'll address that right after this. All right, So, Chuck, there's this kind of there's this idea that if we are regenerating ourselves every seven to ten years, we're like the vast majority of our body cells regenerate, why do we age and why do we die? It doesn't it doesn't really make sense in that respect.

Yeah, it's what they think is it has to do with your DNA actually in the cell. Our cells as we age, even the new ones that get replaced, which really stinks, Yeah, become what they call cinicent, which means that they can't divide any longer. We've talked about the Hayflick limit before, or replicative centizence is basically how many times your cells can divide over its lifetime. Yeah, and I think like a fibroblast, which is the cells of

And we've talked about inflammation kind of being the.

Source of most most of the original problems that will eventually lead to your death.

Yeah, you know.

Yeah, something becomes inflamed and leads to all kinds of problems. There's no repair needed, so it's a false signal. So they're trying to come up with drugs. Now, there's one called wrap a micene that tries to stop the cells from sending out those false signals, which is amazing.

Yeah, that would be wonderful.

You know.

There's another explanation for it as well as that when our cells divide, especially over time as we age, they're basically making photocopies of themselves. Yeah, and you ultimately, years down the road, end up making photocopies of photocopies, right, and those don't tend to pan out very well. So as far as analogies go, that one kind of makes sense that, yes, we have brand new cells, but the DNA copies, the DNA blueprints that they're based on it

Yeah, that makes sense. That's a good way to say it. We also talked a little bit about whether or not the heart muscle itself.

Replenishes itself in the cells, and for a long time they had no idea. But now thanks to our buddy doctor Frisson, his pretty much. I don't even think we said what his who he works with?

Did we?

No?

He works with the with a K. Karolinska team.

Oh yeah, just like incredible scientists that are making like amazing advancements and trying to figure the stuff out. But they did, in fact find that the heart does replace itself the muscle cells. About one percent of the heart muscles were replaced every year at age twenty five, and that falls over your lifetime to less than half a percent per year by the age seventy five.

I spoke too soon. That does make sense.

Yeah, So what they basically said is about half of your heart's muscle.

Cells will be exchanged during a normal lifetime.

Okay, which is okay, it is, but as it's slowing down over time, I mean the heart's kind of essential.

Yeah, but they're hoping again to develop drugs that can accelerate that process too. Yeah, And I don't know how far along they are on that.

But that'd be amazing.

So there's this whole thing that kind of came up to me man like that I don't all of this raises this question to me, right, Yeah, if you look at like you or me or any living things as an investment, like a molecular investment in the ability to reproduce, right, Okay, once you finish your reproductive age, then it does make sense that you would just kind of there would be built in this mechanism of aging and then death and then decay, which is what we do. Yeah, we return

What do you mean?

Like, think about it. If we're just the same as plants, Like.

Why are we all here? Yeah?

Like, if we're if the whole point is to just basically recycle materials, because we are just recycling stuff from the environment, and we're recycled as we die and decay, what is the point? Is our point just to be part of the carbon cycle, So we're moving carbon in and out of ourselves, in and out of the environment, moving it around. Or I don't understand what the point is of life? I guess is what I'm saying here in nihilis No, I'm not saying I don't believe that

Yeah, I think are you about to quit the show?

Yeah?

I see what you mean.

Like, if we look at ourselves as a purely mechanical serving a purely mechanical function right on the planet.

Like we are to the carbon cycle, what say, evaporation is to the rain cycle, Like we're a means of moving something along.

Well, I think that's when you, man, this is getting philosophical. I think that's when you start getting into questions of the soul.

Well, yeah, I mean it kind of makes you wonder like, well, why would there be more than one species? It will be much more efficient to just have one, maybe two. There's all these different ones, so why.

Yeah.

The fact that that why is just sitting there and flashing neon lights definitely made me wonder basically the opposite. It's made me think in a different direction and then nihilistically.

Like, we're only here for so long, and so if there is the point is to like make the most of your time.

Well, I think that's a separate that's a separate part of it. Yeah, because no matter what conclusion you come to, whether Nope, we're just a means of recycling carbon and that is it. Yeah, kind of like a Gaia theory view of things. Or if you say no, like the fact that we're inefficient and redundant as far as that carbon recycling thing goes, suggests that maybe there is a

Yeah, and there are probably others out there that think the whole point is to make as much cash as you can, sure you can buy products.

Yeah, Edward Burnez would.

Probably say that, Yes he would, and he lived that way in Man, that's interesting. I think we should I'd love to tackle something philosophical and deep.

Like the soul meaning of life.

Yeah, that'd be tough.

I mean that'd be cool, though, it would be cool. We don't delve into that very much.

No, we should. I'd like to do that. And consciousness that's a really interesting one too, Like it doesn't make any sense.

It's a very trippy way forward for this show. Yeah, we're gonna start getting weird.

I took a lot of acid this morning. So, oh that's great if you want to know more about some just weird trippy stuff. How stuff works has a surprising amount of it on there. I don't know. Just try typing the word trippy into the search bar. You can also type does your body really replace itself? Every seven years? And it'll bring up this cool article. And I think I said search bar at some point in time. So how about some listener mail?

I like how you specified you took a lot of.

Acid just a little yeah, a lot fun of it?

All right, I'm gonna call this multiple We got like a bunch of emails in one day about people picking at our grammar and things. Oh yeah, so I'm just decided to read three of them because they're short. Hey, guys, I generally enjoy the episodes, but you do have one issue with your grammar and noun verb agreement. You tend to say there are many lines of evidence or there's lots of experiment showing instead of there are not there

Guys. You typically make the mistake about ten times every show.

Why don't you go recycle some carbon power?

That's from Kim Keller in Temple Tariffs, Florida.

Thanks.

I always like to pick apart their emails too, about because people usually make a mistake or two in their own emails.

Hey, guys, this one's from Blair. I love the show. I hate to be nitpicky.

They always say that, don't yeah right.

Before they nitpick, But I have a grammar direction. It's been bugging me for months, and Stonehinge was a major offender. At least one of you not naming names frequently used the word further when you really mean farther. The latter term is used for literal distances. Further is only supposed to be used figuratively.

Huh.

I didn't know that, Okay, so thanks Blair.

Yeah, and then the last one, Phil who was an English and grammar pronunciation freak. He says, hey, guys, when there's an Italian word, you take your time to pronounce it properly. The same with Japanese in the Far East in general. So why don't you extend that same courtesy to English.

Words because we're masters of the language.

And I mean words actually in the UK vernacular, not American English. Salisbury, No, it's Salisbury, the Marlborough Downs, Nope, marl bro Downs.

Well, we're using the American vernacular because we're in America and recording as American.

That's from Phil.

I had I addressed all those I think.

Yeah, I think so. I feel good about it.

I think it's good and very big of you two have read those as listener mail. Why not nice job.

Man, Yeah, we just we don't profess to talk gooder than other people. We just do our little thing here in the studio, send it out into the world nice for people to pick apart.

What we're doing is we're creating grammatical tableaus like that Highlights magazine where it's like pick out the things that don't belong. Yeah, that's what we're doing for you, guys.

Yeah, keep you entertaining if you didn't have something to complain about it, it'd be so boring.

Yeah, if you want to nitpick or compliment or suggest something whatever. If you want to get in touch with us for any reason, you can do that by tweeting to sysk Podcasts. You can join us on Facebook dot com, slash Stuff you Should Know. You can send us an email to stuff podcast at house stuffworks dot com, and as always, joined us at our homeown the web, stuff youshould Know dot com. Stuff you Should Know is a production of iHeartRadio.

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