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Jessi: Hi guys! Do you want to try something neat? Take these two fingers, now hold them on the side of your neck right next to your throat. If you hold them still for just a moment, you'll start to feel something bumping around in there.

That is your pulse, the feeling of blood moving through you body, and that means your actually feeling your heart beating. Your heart is always beating, all day and all night, even when you're asleep. It can never take a break because it has a very important job, it moves your blood all around your body.

And your heart can do that because it's actually a muscle. You have muscles all over your body that help you move, like muscles in your legs that you can use to run and muscles in your jaw for chewing yummy food, but your heart is the hardest working muscle of them all.

Now, make a fist with your hand. That's about how big your heart is. It may seem kind of small, but it's incredibly strong, and it's the constant squeezing of your heart muscle that keeps all that blood flowing.

But why does your blood have to move around in the first place? Well, you can think of your blood as working kind of like a delivery truck. It carries lots of what your body needs to keep going, especially oxygen.

You've probably heard of it before, oxygen is the gas in the air that people and a lot of other animals need to live. When you breathe in, you're bringing oxygen into your lungs, and your blood is there to soak up all that oxygen and, with the help of your heart, send it all over your body, to your head and to your feet and everywhere in between.

As your blood gets pumped around, all of your different parts of your body take the oxygen from it and they use it to do their jobs, whether that's making your leg muscles move so you can run, or helping your stomach take care of that sandwich you had for lunch.

But your body also has a bunch of stuff that it needs to get rid of, especially a gas called carbon dioxide. So after your blood drops off its shipment of oxygen, it also picks up that waste and hauls it off. When your blood gets back to your heart, it gets pushed to the lungs once again, where the blood drops off the carbon dioxide and picks up more oxygen.

So when you breathe in, you're breathing in oxygen that goes into your blood, and when you're breathe out, you're breathing out the carbon dioxide that your body has gotten rid of.

Now, it sounds like a long journey, but your heart can pump blood to every part of your body in less than one minute. And your heart beats one hundred thousand times every day, so at any point during your day, your heart is sending blood to your lungs, and out to the rest of your body, and back to your lungs again all at once. That's some serious work!

But have you ever noticed your heart beating faster when you're been running around for a while? That's your heart working extra hard. When you're running, jumping, and playing around, your body needs more oxygen and other nutrients to do that extra work, so your heart has to work harder to send all of those good things to the parts of your body that need them, and to get rid of all of the extra waste.

So the more you exercise your body, the more you exercise your heart. Now, who's up for some jumping jacks to get our hearts beating faster?

And if there's something that you'd like to learn more about, just let us know by asking an adult to help you leave a comment below or email us at kids@thescishow.com and we'll see you next time.

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