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Hank was having a conversation with some of our SciShow friends
on the podcast, SciShow Tangents.
And the episode was about food, but as the podcast’s name suggests,
they went on a tangent about crocodiles that kind of blew my mind.
So, let’s get straight to the heart of the matter…
the crocodile heart: it has an extra valve.
And although researchers are still trying to understand why, they have some ideas.
Crocodile and human hearts do have a lot in common.
For instance, there are really only two places our hearts send blood:
They either send it to the lungs or to the rest of the body.
Ultimately, that’s because we’re both using our circulatory systems
to move around oxygen.
Blood picks up oxygen from our lungs, and then gets propelled through the heart
to deliver that oxygen to all the cells in our bodies.
Then, by the time blood returns to the heart, your cells have used up that oxygen,
so your heart shuttles the blood back to the lungs to pick up more.
And when all of that works as it should, it helps to keep you alive.
But human hearts and crocodile hearts have a very important difference.
Under certain conditions, crocodiles don’t send their blood back to the lungs
when it returns from the rest of the body.
They can instead send that blood back out to the body through an extra valve
that humans don’t have.
They don’t do this all the time.
For them to use this extra valve, two things have to happen.
One, they have to have enough blood pressure built up in the chamber
leaving the heart to open the exit valves.
And two, they have to be lacking adrenaline.
That’s because scientists found that adrenaline injections
can close up the extra valve on command.
In nature, this means that when the crocodile’s fight or flight response kicks in,
they’re directing blood to pick up more oxygen
to prepare for whatever they are fighting or fleeing.
So the extra valve is probably used more in calm times
when the crocodile is just hanging out doing it’s thing.
But why have this extra valve in the first place?
Kind of surprisingly, one group of scientists found that this valve
doesn’t seem to help these animals be bigger, better crocodiles.
They think it might just exist because it hasn’t been evolutionarily selected against.
In other words, it’s not causing any harm, so it hasn’t evolved away.
It’s just kind of along for the ride.
Alternatively, another research group suggested that it might have something to do
with diving, because the valve opens more when crocodiles go underwater.
Since crocodiles aren’t breathing while they’re underwater,
the amount of oxygen in their lungs goes down over time.
So, some scientists think that they may be using this extra valve
to re-circulate their blood and pull as much oxygen from it as possible,
before they send the blood back to the lungs for more.
Since we don’t do nearly as much swimming and diving as crocodiles do,
this might explain why they have this valve and we don’t.
On the other hand, maybe the answer is something else entirely.
Yet another team found that more blood gets sent through this extra valve
during digestion, so maybe it helps with that somehow.
More specifically, when researchers closed off the extra third valve,
crocodiles that had just eaten made less gastric acid
than the other crocodiles with all of their functioning heart valves.
Crocodiles use gastric acid to digest their food,
and a key ingredient in making this acid is carbon dioxide.
And CO2 isn’t just one of the ingredients, but the first to run out in this process.
So researchers have suggested that this extra heart valve could be
sending carbon dioxide to a crocodile’s digestive system,
allowing them to make more gastric acid and digest their food better.
In the end, the reason for this difference between humans
and our scaly crocodile friends is just not conclusive, at least for now.
Like, it might not even be an adaptation.
This might have just been a divergence that stuck around without rhyme or reason.
But it also could be helping them do daily activities like diving or digesting.
Either way, sometimes the discovery on its own is enough to be mind-blowing,
even when we haven’t yet figured out why it is that way.
Thanks for watching this episode of SciShow!
And thank you to this month’s President of Science, Matthew Brant.
Your generous support helps us keep making free science videos like this one.
We appreciate it, and we appreciate you!
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you can head over to patreon.com/scishow.
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