Why Crocodiles Have an Extra Hole in their Heart

Crocodiles have four-chambered hearts, just like we do! But, while our hearts do just fine with four valves, they have a slightly different approach…

Hosted by: Stefan Chin

----------
----------
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever:

Tomás Lagos González, Sam Lutfi. Bryan Cloer, Christoph Schwanke, Kevin Bealer, Jacob, Jason A Saslow, Nazara, Tom Mosner, Ash, Eric Jensen, Jeffrey Mckishen, Matt Curls, Alex Hackman, Christopher R Boucher, Piya Shedden, Jeremy Mysliwiec, charles george, Chris Peters, Adam Brainard, Dr. Melvin Sanicas, Harrison Mills, Silas Emrys, Alisa Sherbow

----------
Looking for SciShow elsewhere on the internet?
#SciShow
----------
Sources:

Images:

[richardbidinger]

Increasing gastric acid sounds like the most relevant idea. Alligators don't chew their food and swallow everything whole, so you don't have little bits mixed up with stomach acid which would digest quickly. For an alligator, everything goes down including the bones and I'm pretty sure they don't regurgitate any of back up, so they're going to need to make sure they don't have rotting animal carcasses hanging around in their guts.

[atgsleepless]

Human fetal hearts actually do have a shunt between the two atria (called foramen ovale), which prevents the blood from going through the lungs since they don't breathe air just yet.

[anthonyx]

From an engineering point of view, bypassing the lungs when they're not necessary (as when diving and not oxygenating the blood), could make the circulatory system more efficient because the heart isn't doing useless and therefore wasteful work.

[dorabrooks]

Every time I think crocodilians can't get any cooler or more interesting to me, some information like this comes along and blows my mind! Seriously some of the most fascinating creatures ever!

[evilsharkey]

Humans have an extra valve, too, but it (usually) seals up when we’re born. It mostly bypasses the lungs until we’re born and need to use them because we can’t get oxygen from our mothers anymore.

[Agmolly]

Me, born with a hole in my heart: 😮 _I’m half crocodile_ 🤩

[penguinista]

They are insanely well adapted and have not changed for eons, so it is very hard to believe that this major a design feature is not useful.

[IntellectualBlackhole]

The extra hole is to let in the extra love

[jtjames]

Holy moly that's brilliant!

So crocodiles can reduce their CO2 by creating gastric acid. Running out of oxygen isn't nearly as troublesome as having too much CO2.

Now I want a cybernetic way to remove gastric acid, or at least neutralize it, ulcers suck. Be able to hold your breath for a ridiculously long time.

An internal rebreather.

This would be incredible useful for Martian colonists. If you run out of air have your neurolink send you into a hibernation mode. Give you significantly more time for rescue.

Kim Stanley Robinson actually proposed using it crocodile DNA to make humans more CO2 resilient. Might as well take it the other step and add an extra valve.

I'm still trying to figure out a way to install actual pumps in my legs to reduce my blood pressure. Or increase it for superpowers. Gravity is a b****.

[TheBitPianist]

The explanations are all incredibly interesting. Reminds me of the tons of different theories why our ancestors began to walk on 2 legs, I want all of them to be true

[BNails]

I'm no crocodile expert, but I would make a guess that it has a lot to do with energy conservation.

If a croc is just hanging out doing nothing, it needs very little energy. Why waste the energy stores it has on pointless circulation.

Meanwhile we don't have this because we were never really on the top of the "oh god, run!" food chain as crocs are. Not many animals are actively hunting crocs, unlike humans. We needed the constant ability to move fast and **right now**. Crocs rarely have to do this other than to prey on another animal.

[a.kitcat.b]

I love any reptile so hearing any random fact impresses me. Its extremely interesting to learn about something that has no clear reason to exist...but it does.

[victoriawilliams]

This information is so frickin fascinating.

[AliHSyed]

Nobel prize for the scientist that observed a croc on adrenaline.

[Ichithix]

When I was a kid I read a short story about a scientist who fixed the hole in crocodile hearts and they (re)evolved into dragons. Oops.

[jasonfabo]

What a ballsy human to inject a crocodile with adrenaline

[purplealice]

I was just watching a live camera feed of an alligator named Rex, at Snake Discovery on Twitch. She's a rescued gator whose growth was stunted by having been kept in a too-small enclosure when she was small.

[arnearne]

given that the valve affects all of these scenarios a little bit i think it's fair to say that just like having opposable thumbs it's not specifically for one exact task it most likely benefits the crocodile greatly in it's normal life to have this valve

[forrestgreene]

Was hoping the answer was, "Because they don't know how to love."

[TheSquire]

In your brief, hand-drawn diagram of the circulatory system you mislabeled the pulmonary artery and vein. Arteries and veins refer to whether blood is going to/from the heart, not whether or not the blood in it is oxygenated