shows you really neatly where the heart sits in our body

so you can see the heart is surrounded, on both sides, by ribs, right?

And in fact, I didn't draw it in yet, but let me show you where the

lungs would be. This is the right lung

and on this side you'd have the left lung. So this is where

your heart sits: between two lungs. And I'm saying

left and right from the perspective of the the person who owns this

heart. So this is their left and right, which is the opposite

of us if we're looking at it. The heart is actually sitting between the two

lungs within this protective casing that

the ribs are basically there to keep all these important organs

safe. And then below them, so if you draw

this here. Or if I draw it, you can

see now that below all this stuff is

a really really important muscle. So this muscle

people don't talk about this muscle, or this is not the kind of muscle

that you usually see people working on at the gym, but this muscle is called the diaphragm.

So your diaphragm muscle

and your ribs are enclosing a space, right? The diaphragm becomes the floor, and the ribs are kind of the

ceiling and the walls of this space.

And if you look at the contents of this space, you'd have your lung

and you'd have your heart. So, this entire space then

is called your thorax.

So what exactly does the heart do? Let's actually make a little bit of

space now, and bring up a

zoomed in version of the heart.

Let me start by orienting you to the heart. This is our right lung

and on the other side we have our left lung. And all this would be

inside of the rib cage, but I'm not going to draw that now, because that would

make it harder to see the heart itself. So to think

about exactly what the heart does, I think one, kind of neat way to do it is

to actually imagine that you're a cell. So put yourself in the perspective

of a cell, and let's say you're a cell hanging out

over here. This is you. And you can

think about any part of the body that you could be. Let's say a little

toe cell. So let's say you're a toe cell

and your job, of course, is to live and be happy,and you've got

near by, a little blood vessel. And in fact, every cell in our body

has a little blood vessel that's near by. And this toe cell

is just trying to make a living. And toe

cells need certain things, right? They need, for example, let's say oxygen.

I'll write it in white so it's very clear. They need oxygen

and they need nutrients, right?

So cells need certain things to live and be happy.

And on the flip-side, they also make waste. They're in

a sense just like us, they make waste. And that waste could be

all sorts of things, and one that kind of jumps to mind is

carbon dioxide (CO2). So carbon dioxide is waste

for this cell. So it's making some

waste and for the moment let's imagine that there's no blood flow.

So, even though there's a blood vessel near by,

really, no flow is happening, so I'll just write "no flow".

So as the little cell

makes waste. That waste, let's draw a little ball right here,

it's going to start accumulating, you're going to start collecting more and more of it

since the blood is not really flowing. And it might kind of

end up getting all the way around our toe cell. So our toe cell is getting

swamped, literally getting kind of covered by its own waste.

And on the flip-side, is it getting oxygen or nutrients? No.

It's not getting either of these things. So, before very

long, I would say within minutes, our toe cell

is thinking, "Well this is not a very happy way to live!" this is

actually really very sad, this is awful. And if this continues

the toe cell would die. So, what a toe

cell needs, and what every cell needs, and that could be a finger cell or a

skin cell, or really any cell that's living, needs

flow. Right? It needs this blood to be flowing nicely

and smoothly. And if there is flow

then you get a very different picture, right? If there's flow then all the sudden all the

waste product is actually now lifted and taken away.

It's flowing away, and it's a little bit like having

someone come by and pick up the trash, then you don't have trash all over the house.

So then you have nice flow, and

in return, oxygen and nutrients are delivered. So this stuff

gets delivered as well. So, all of the sudden the cell is going to be

very, very happy, and is going to be living just fine.

So, really if you want all of the cells in your body to be living just fine

like this cell here, you really want good flow throughout the

body. And so this is really point number one. Is that you really

need, somehow, to have blood flow moving and pushing

blood constantly through the body. So,

to do this for billions and billions of cells you would need a pretty powerful

pump, right? Something that's going to be able to pull

in all the blood from the body, and then push it back out. And that's what the heart

is. I mean at its core, that's exactly what the heart is doing.

It's an amazing pump, pushing blood, so that

you have good blood flow. And so I'm

going to write that on the side as kind of job number one. These are the jobs of the heart.

So jobs, and number one, would be

blood flow. And I'll write systemic

flow. Systemic flow. And all

that systemic means is that I'm refering to the entire body. So systemic

when I say that word, I just mean the entire body. All the cells

in the body. Now, exactly how that happens actually

you can see on this picture. So, here you have a giant

vein, this is a vein, and you have an artery.

This is an artery.

And blood is actually going through the artery, that way.

And it's actually coming into two veins, the one

at the top, this is called the superior, superior just kind of means

at the top. Superior vena cava. That's the

name of the vein. And at the bottom here, you can't see it because

it's on the other side of the heart, but there's another vein called the inferior vena cava.

And these two veins, this is also a vein,

these two veins are actually dragging blood in from all over the body,

into the heart.

And then, when the heart is ready to pump it back out, it goes into this

artery, and the name of it is the aorta.

So if you've heard of the aorta, this is the artery that people

are talking about. So this is how blood comes and gets pumped

around. But this isn't actually the only job of the heart. The job,

the second job of the heart, is actually

also in this picture, and it's called pulmonary flow.

Pulmonary flow. So, what does that

mean? Well, we know that cells are expecting

oxygen, right? We know this. And that they have a lot of carbon dioxide

waste. Well, it's good to move things around. It's good

to move blood around. But if you actually never got rid of that carbon dioxide

or brought in new oxygen, then a cell is not going to be very happy either.

I mean, you can have blood flow, but at some point it's also going to want some oxygen.

And it's going to want to get rid of that carbon dioxide. So, that's where the

lungs come in. So what happens is that the heart, before

sending blood out the aorta, before just dishing it out back into the body,

it actually sends the blood over to the

lungs. And it goes over to the left lung, and over to the right lung.

And the blood comes back from the right lung

and the left lung, and gets pushed back into

the heart, and then gets squeezed through the aorta. So there's this

actual extra little step here, where blood is going to

and from the lungs, and that's the pulmonary flow.

So the final thing you'll notice, if you look at this picture it's hard not to notice,

is that there are these, kind of wriggly looking little

blood vessels all over the heart. And what are these

exactly? I mean, you've got red ones, and blue ones, and

the blue ones are the veins, and the red ones are the arteries

but are they part of the systemic flow, or pulmonary flow, or something else?

Well, these vessels, all of them,

together are called coronary vessels.

And so specifically you might hear about

a coronary artery, or a coronary vein, but together you can call them

coronary blood vessels. I'll add the word blood here. So these

coronary blood vessels are actually serving the heart muscle

itself. I mean remember, the heart

is made up of thousands and thousands, actually tens of thousands of cells

and those cells, just like our toe cell that we drew,

they also need oxygen, nutrients, and have waste.

So, those cells are going to need blood vessels supplying

them as well. So, that's what the coronary blood vessels are. They're literally

the blood vessels that go to and serve

the heart. So these are the ones that serve the heart.

Now, if they're serving the heart muscles

and the heart cells, then, think about it, would they fit under

the systemic flow, or pulmonary flow? Well if the

main job is to serve the needs of cells, then

the coronary vessels fall under the systemic flow.