The human body replaces millions of cells every day. Here's how much skin, blood, and saliva it can produce in a lifetime.

  • The human body can replace 20 million cells in just a few seconds, which means over a lifetime, your body produces a lot of hair, blood, saliva, and skin.
  • Our bodies shed a whole layer of outer skin every two to four weeks.
  • Your liver can regenerate itself – sort of like how a starfish can regenerate lost limbs. A healthy human can lose 65% of their liver and ultimately be ok, since it would grow back over a few months.
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Following is a transcript of the video.

The average lifespan for Americans is 78.5 years. That’s a total of 2,477,300,000 seconds. But let’s break that down. By the time I finish reading this sentence, 20 million new cells have just been replaced in your body. 20 million, in just a few seconds. Compound that over a lifetime, and, well, your body achieves some pretty incredible feats.

Let’s start with our largest organ: skin. It reproduces about 30,000 to 40,000 cells every minute. That means we shed a whole layer of outer skin every two to four weeks, or 1,000 bodies worth in a lifetime. And underneath your skin lies a vast network of blood vessels. Spread out, this network of veins, arteries, and capillaries would extend over 100,000 miles. That’s long enough to wrap around Earth’s equator four times. And through those blood vessels, the heart pumps about 7,500 litres of blood every day. That’s an estimated 215 million litres throughout your life. Or enough blood to fill a whopping 86 Olympic swimming pools.

Now, the red colour in your blood comes from hemoglobin proteins and iron. You get that iron mainly from your diet. Which is then absorbed into your bloodstream from your gut. The average adult will have 3 to 4 grams of iron at any given time. But will lose and replace 1.5 milligrams every day. So over a lifetime, you’ll absorb at least 43 grams worth.

That’s equivalent to 10 standard iron nails. And speaking of 10 nails. Your fingernails grow at a rate of 3.5 millimetres per month. That means, if you went your entire life without ever cutting them….they could get to more than 3 meters long. Shridhar Chillal, for example, stopped cutting his nails when he turned 14. And before he finally cut it when he was 82 his thumbnail was almost 2 meters long.

But your fingernails grow at a snail’s pace compared to your hair. On average, each hair grows 12.5 millimetres per month. So, over a lifetime, that’s about 12 meters of hair! Almost the length of an American school bus. And if you look at what else your head produces on the regular, saliva is a big one.

You produce on average 1 litre every day. That’s about 28,600 litres over a lifetime, or enough to fill 39 four-person hot tubs. But believe it or not, you actually produce more mucus and snot each day than saliva. About 1.4 litres. That’s about 54 hot tubs worth over your lifetime. And the best news you swallow most of that.

OK, all that liquid goes somewhere, so let’s talk about the other end and our urine. The average healthy adult produces anywhere from 400 to 2,000 milliliters a day. Or on average, 34,400 litres in a lifetime. That’s enough to fill 46 hot tubs, gross.

Now, that might seem impressive, but it has nothing on one of your biggest, most important internal organs: your liver.Your liver can regenerate itself – sort of like how a starfish can regenerate lost limbs. That’s thanks to the enormous amount of regenerating cells in your liver. In fact, a healthy human could lose 65% of their liver and ultimately be no worse for wear, since it would grow back over just a few months!

So when you think about it, your body is like a mini factory, generating loads of cells and fluids daily. But not all your body parts are able to reproduce, your inner ear hairs in charge of hearing never regrow.

So if they get damaged, your hearing will suffer, or worse, disappear, and even the most important organ in your body – your brain – doesn’t produce that many new cells. You’re born with roughly 90 billion nerve cells in your brain, called neurons. And lose, on average, 60 of those neurons every minute.

But during a traumatic brain injury, like a stroke, the brain can lose millions per minute.That said, the human brain can still recover from this loss thanks to something called plasticity. Plasticity describes how our brains’ remaining neurons take on different roles and form new connections to make up for any important connections that were lost.

So, whether it is adaptation or regeneration. Our bodies go on quite a remarkable journey. So the next time you get a paper cut, try to look on the bright side of things and give thanks to those hardworking cells fixing you right back up.

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