Name: Why Can We Regrow A Liver (But Not A Limb)?
Uploaded: 2017-02-17T05:00:29.000Z
Duration: 4 min 7 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Flatworms can regenerate over half their bodies.

And if a predator grabbed this lizard's tail,

she could break it off and regrow it later.

It would be really awesome if we could regrow limbs

The closest we can get is kind of, sort of

of lots of different kinds of cells, from nerve cells

And our cells are constantly dying or getting

So we need to be able to make more of them.

When we're embryos, our stem cells are superpowered.

might need and help grow everything from our stomach

But as adults, our stem cells lose the superpower.

Adult stem cells can't become just any sort of cell.

While certain stem cells in our bone marrow

have to become either blood or immune cells,

stem cells in our intestine have to become intestinal cells.

There's no way either of these stem cells

will ever become, say, a liver cell or a nerve cell.

Lizards don't ever lose their stem cell superpowers.

When a lizard's tail falls off, a bunch of pluripotent

stem cells rush to the stump and form this mass called

The pluripotent stem cells will differentiate

into skin cells, muscle cells, or bone cells--

Scientists think it's an evolutionary trade-off.

Those lizards have small bodies and would take one of them

But it would take a lot more time and energy for one of us

to regrow a whole arm, plus the added energy it

takes to keep the pluripotent stem cells in reserve.

So instead of wasting all that time and energy,

we just grow some scar tissue over the wound

But our livers are a little bit different.

And it helps with digestion, stores nutrients

and immune signals, and filters waste from our blood.

So we've evolved to protect against that.

Turns out that even if you lost 75% of your liver,

the remaining liver cells could grow and divide

The sort of regrown liver isn't coming from stem cells, though.

So the structure won't be quite the same as the original.

So this isn't true regeneration like with a lizard's tail.

But the liver will function well enough to keep you alive.

grow a new one in this tissue culture lab,

The problem is that liver cells don't survive long enough

outside the body to grow into enough tissue to transplant.

Scientists at MIT's Lab for Multiscale Regenerative

Technologies are trying to solve this problem.

How can we mimic the human body's environment

For example, other organ cells, like the ones

in your heart and brain, don't divide like liver cells.

Researchers are finding ways to trick them and stem

cells to someday regenerate those organs and other body

So for now, our reptile friends have one-upped us.

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