Can you guess what I am?

I'll give you a hint...

I have a very important job inside your body

and your heart helps me to do my job.

I'm a red blood cell!

My job is so important that you'll thank me for it later!

But I can't take all the credit.

Without your heart I couldn't do a thing!

You see, I'm like a little delivery truck in your body.

I pick up and drop things off all the time.

I ride the highways of something called

the circulatory system.

I like to call it the Circle System

because I keep going in circles!

This system is made of your heart and blood vessels

that carry your blood to different areas of your body.

Your blood vessels are like tiny tunnels

that run all through your body.

They are made up of arteries that take oxygen

to places in your body,

and veins that take carbon dioxide

from your body to your lungs.

This is MY highway.

But I can't move by myself.

I move within your blood when it moves.

How does your blood move, you ask?

Why, your heart pumps it.

Let me show you how.

Your heart is the most important muscle in your body.

It moves by itself and even though you can hardly feel it,

it keeps moving all the time,

even when you are sleeping.

Want to feel your heart move?

Sit very still and put your hand on your chest.

If you were running hard or exercising

you might find it easier to feel.

When your heart moves it's called a "heartbeat".

Your heart makes at least 100,000 heartbeats every day.

When your heart beats it pulls blood into it

and pushes it out again.

This helps the blood to move fast enough

to go through your whole body and back.

And it helps me to pick up my deliveries

and take them to different places in your body.

I'm not alone in there.

There are lots of red blood cells just like me

doing the same thing in your body all the time.

Even now, while I'm talking to you!

Here's me at the start of my little journey.

I just got back from dropping off some things

to some places in your body.

I need to get some more speed to do more deliveries

so I ride your bloodstream into your heart.

Going through the heart is easy because the heart

has special rooms and doors that only open one way.

Right now I am entering the right side of the heart.

I go through the first room called the "right atrium",

through the first door called the "tricuspid valve",

and through the second room called the "right ventricle",

and through the second door called the pulmonary valve.

The heartbeat causes the heart

to squeeze the blood in these rooms into the next area.

It pushes the blood through it and into the arteries

(like tunnels) that lead to other parts of the body.

So, now I'm moving a little faster

cause the heart has given me a push.

Now I need to go and pick up the things I need to deliver.

My first stop is to the lungs.

I need to pick up a little oxygen molecule

to take to someplace in the body.

Every body needs oxygen.

Our lungs bring it into our body,

and then I pick it up and take it to where it's needed.

It seems like it would be tricky to pick up the oxygen,

but the lungs really help me with that job.

You see, here in the body we all work together

and co-operate to keep everything running smoothly.

When I get to the lungs...

(I'm not really this big, it's just easier to see me this way)

... and I get really close to the sides of my little tunnel...

... the oxygen that is sort of floating out of the walls nearby

just jumps onto me for the ride.

When enough of it has hopped on and I can't hold anymore

then I'm ready to go back to the heart for another push.

Know what?

This all happens so fast that it's even faster than blinking!

So now this time I need to go in the other side of the heart.

This side is for all of us red blood cells

that are carrying oxygen.

The heart pushes us a little farther this time

because some of us have a very long trip.

I go in through the first room called the "left atrium"

through the "mitral valve" "doorway"

and into the "left ventricle" room to get my big push.

Then out I go and on my journey!

I like my job because I get to travel.

Here I am making a delivery in the foot area!

All I have to do is draw near to the tunnel wall

and the oxygen will just jump out of my truck

and squeeze out of the tunnel!

It's pretty neat to watch.

While this is happening I also make another pick-up.

Carbon dioxide needs to be taken up to the lungs

so that the body can get rid of it by breathing out.

And I'm just the cell to do it!

I grab some and off I go again.

Going back up to the heart is a little tricky

because I need to ride up.

It's kind of like climbing a hill.

Because of this the veins have little trap doors called valves

that only open one way.

This stops me from floating in the wrong direction.

So I keep going up and up as the heart

keeps beating and pushing the bloodstream along.

Eventually I get back to the heart again

where I get ready to drop off the carbon dioxide in the lungs

and get a good push to get me going on another pick-up.

So that's my job! What do you think?

Pretty important isn't it?

The heart really helps me to do my job well!