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Fun Fact: people can donate over half of their liver, and the tissue will grow back within a year! Knowing that, it seems pretty logical to assume that we could just keep donating and regrowing our livers over and over again, but is that really the case?

Special Thanks: Dr. George Michalopoulos, University of Pittsburgh School of Medicine and Medical Center

Hosted by: Hank Green

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Sources:
Dr. George Michalopoulos, personal communication
http://science.sciencemag.org/content/276/5309/60
https://www.mayoclinic.org/diseases-conditions/toxic-hepatitis/symptoms-causes/syc-20352202
https://link.springer.com/article/10.1007/BF02889179
http://onlinelibrary.wiley.com/doi/10.1002/hep.20969/full
http://onlinelibrary.wiley.com/doi/10.1002/hep.20214/full
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2701258/
http://onlinelibrary.wiley.com/doi/10.1111/j.1432-2277.2005.00158.x/full
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3976740/
[♩INTRO].

Here at SciShow, we recently learned a fun fact: You can donate over half your liver to someone who needs a transplant, and the tissue will grow back within a year. So then we got super curious: Could you just keep cutting chunks off and donating them and regrowing your liver, kind of like donating blood, except it's an organ?

Turns out, the answer is no. Which is kind of a bummer, because that would’ve been cool. But the reason why is actually really interesting: It’s because of how the liver cells get replaced.

Liver regrowth in humans is pretty amazing. In a study of 27 living liver donors, it took only about a month after donation for their liver function to return to normal, and less than a year for their liver to regrow its normal mass. And you could probably regrow your liver more than once.

In one study, a very unlucky rat had part of its liver removed again and again, and supposedly it grew back 12 times! That being said, rodent livers have a different structure than ours, so it might not work exactly the same in us. But even if it’s possible to donate part of your liver more than once, transplant doctors probably wouldn’t recommend it.

First of all, even though it’s pretty safe if you’re under age 60 and healthy, it’s a major surgery. And the bigger problem is:. The regrown liver chunk likely wouldn’t do any good because the liver regrows, but it technically doesn't regenerate.

True regeneration occurs in some animals, like salamanders. If a salamander loses a leg, cells near the cut dedifferentiate. In other words, they revert to an earlier developmental state.

They basically become the cells in an embryo that have no specific job, but they have the potential to turn into tons of cell types, from bone to skin to muscle, depending on what molecular signals they get. Then they multiply, divide up into groups, and respecialize into the cells that make up a leg. It’s essentially a redo of what happens as the salamander embryo develops, so the leg structure is the same, and the scientists consider it regeneration.

Good as new! But this isn’t what happens when part of your liver gets cut off. Instead of all this dedifferentiation, what mostly happens is a variety of mature liver cells just multiply to make up for the loss.

The regrown tissue has some structure, but it doesn’t replicate the exact layout of a fresh liver, from cell organization to the arrangement of blood vessels. So even though the regrown liver is fully functional, it’s not true regeneration. Technically, what your liver does is called compensatory hyperplasia.

This different structure would make it harder for transplant surgeons to safely remove a portion of a repeat-donor’s liver. It’d also be harder to connect that regrown chunk to the transplant recipient’s blood vessels so they could actually use it. So even though a liver donation can save someone’s life, doing it more than once isn’t a good idea for you or the person who needs the help.

Thanks for watching this episode of SciShow! If you want to learn more about how weird the human body is, you can check out the video that inspired this question, which is all about organs you could live without. [♩OUTTRO].