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  • Hi, I'm Adam Cole.

  • This week we've got a question from Lulu Miller, the host of NPR's Invisibilia podcast:

  • How old are our bodies actually?

  • Because if you think about how we're constantly being regenerated our physical matter is being shed and replenished... what actually remains?

  • Good question, Lulu!

  • Well, your hair obviously doesn't remain the same and I'm not just talking about the style.

  • Each hair on your head is replaced every 2 to 7 years.

  • A hundred hairs fall out every day and new ones grow back in their place.

  • And look at your fingernails - they're completely new every six months or so.

  • It turns out it's just a matter of time before almost every part of your body refreshes itself in a similar way.

  • The lining of your stomach and intestines gets pretty beat up -- it's constantly exposed to acid and bile and so those cells get replaced every few days.

  • Every few weeks, your outer layer of skin is completely renewed.

  • Every four months you have a fresh army of red blood cells.

  • A hundred million new cells are born every minute and a hundred million old cells are destroyed.

  • It's actually the breakdown products of these red blood cells that turn your bruises and urine yellow.

  • Every 10 years, you've got a new skeleton.

  • A special team of cells breaks down old bone, and another builds new bone.

  • Every 15 years your muscles are refreshed.

  • You might think you gain and lose fat cells when you gain and lose weight but they actually just get bigger and smaller.

  • Over the course of 25 years though, most of them turn over.

  • But there are a few things that stick around for your entire life.

  • About half of your heart stays with you from birth to death because those cells are replaced very slowly.

  • Certain parts of your brain add a few new neurons over the course of your life but the vast majority of your neurons developed before you were born.

  • It's the connections between those neurons -- the circuits that store memories that are constantly changing.

  • And there's one more part of you that lasts your whole life.

  • Months before you were born, a little cluster of cells stretched and filled themselves with transparent protein.

  • As you grew, even after birth, more and more fibers were added, but that center endured

  • This is your lens the window through which you are watching this video right now, and its core has remained the same since the moment you first opened your eyes.

  • So how old is your body really?

  • Some of it is brand-new and some of it is as old as you are.

  • To learn how scientists figured all this out, check out our post at skunkbear.tumblr.com

  • And listen to Invisibilia -- the latest episode is about whether or not personality persists throughout your entire life

  • If you have science questions send them our way and please subscribe to our channel!

Hi, I'm Adam Cole.

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Your Body's Real Age

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    VoiceTube posted on 2016/07/19
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