I'm still alive. And I am. I'm going at about 60 beats per minute and it will continue doing

that throughout the podcast and hopefully throughout the rest of my life. Because the

circulatory system is important, it moves oxygen around my body. It moves carbon dioxide

out of my body. It moves nutrients to the cells in my body. And so we need it to keep

beating. And it does. Something that we kind of take for granted. Before we get to the

elements of the human circulatory system you should know that there are different types

of circulatory systems. In things like insects and spiders they don't have blood per se.

They have something called hemolymph. And that hemolymph is going to be both blood and

what's called interstitial fluid. Interstitial fluid is going to be the fluid that bathes

the cells inside us. In an insect those things are combined together and that's why if you

squash a bug you get that goo that comes out of the bug. But in us we put our blood inside

blood vessels and then the interstitial fluid is going to be everywhere else inside our

body. And so we keep those separate. And so that's the difference between a closed and

an open circulatory system. In animals we also have a variety of different hearts. And

so a fish, something like this that lives in water, it simply has a two chambered heart.

And so it's heart has 1, 2 chambers. It's separated by a valve and the reason why is

that they live in water. And so when you're looking at the pictures of hearts on the next

few slides, I don't want you to look at the heart as much as I want you to look at the

loops that come from that. And let me make it a little simpler. I'm going to get rid

of half of this diagram. Because half of it is just the left side of the fish. Okay, so

if we look at it what do we have? We have one single loop. So the blood is going to

go to the gills where it's going to get oxygen and then it's going to go to the body and

then it's going to continue back to the heart. So we only have one loop. And that works great

in water. But when you move onto land you lose quite a bit of that pressure as you go

to the gills, or if on land as you go to the lungs, and so it simply isn't a system that

works. And so that's why on land we have a three chambered heart. So things like this

bearded dragon over here have a three chambered heart. What does that mean? Well let me again

draw it right down the middle and get rid of half of the diagram. This makes it easier.

What we now have is we have two loops. And so we have one loop that goes to the lungs

and then it comes back to the heart. And then we have another loop that goes to the rest

of the body. And so that deals with that pressure issue. But one thing that's interesting is

that instead of just having red and blue blood we now have this purple blood. What does that

mean? We're getting a mixing of the blood. In other words we're having a mixing of the

oxygenated blood in the red and the deoxygenated blood in the blue. An that's because we only

have 1, 2 because these ones are combined, 3 chambers in the heart. And so once we become

endothermic, one we become warm-blooded and need quite a bit of energy, that's not efficient.

And so in birds and mammals we have a four chambered heart. And so basically what we've

done is we've sealed up that third chamber. Now we have one, two, three, four chambers

to the heart. We still have a double loop. And so that's more efficient. And those have

evolved as we've had different constraints depending on the environment and where they

live. So what does blood do? Blood follows a loop. And so it's going to start at the

heart. It's going to move throughout rest of the body in arteries, arterioles eventually

down to capillaries and then come back again. And so it keeps moving around your body. It's

moving nutrients and it's moving that carbon dioxide out and it's moving oxygen to the

parts of your body that need it. Let's start with the heart then because it's important

that you understand the chambers of the heart and where blood is essentially going. Whenever

you see a diagram like this you want to kind of imagine yourself shifted into the heart.

So imagine yourself in this heart right now kind of turn yourself, in your brain, inside

it. So basically your right side now is going to be over here and your left side is going

to be over here. And so that's pretty important. So let's start with deoxygenated blood. Deoxygenated

blood means that it's coming back from your body. So where does it come from? It's coming

from your superior and inferior vena cava. So basically it's entering into what's called

your right atrium. So this would be your right atrium here. So we've got deoxygenated blood

coming back, it's in your right atrium. It then goes through this valve here. This valve

is called the AV valve. Sometimes we call it the tricuspid valve, but the blood is now

going to go from here into the ventricles. So it's going to go into your right ventricle.

It's then going to move out through this semilunar valve, semilunar valve, it's going to move

into what's called the pulmonary artery. So this would be the pulmonary artery here. What's

interesting about the pulmonary artery is it's an artery that has deoxygenated blood.

And the reason why is it's headed to the lungs. So the blood is going out that artery. That's

what an artery is. It moves away from the heart into the lungs and now it becomes oxygenated.

So that oxygenated blood is going to come back into here, that's going to be your left

atrium. And I can't write on that because you won't see it. So it's going to go into

your left atrium which is right there. It's then going to flow through our left AV valve

down into this ventricle. So this would be our left ventricle inside there. And then

it's going to be move out the back into this big artery. And that's called the aorta. So

it goes through the aorta. So there's an aorta down here and then this aorta as it move up

here is going to send up arteries that go up to the head. It's then going to go to the

body and then it's going to come back again. And so I should be able to clear all of those

out and you should pause the video right now and can you do that? Can you go form the superior

and inferior vena cava all the way to the aorta? And if you can, awesome. If not, you

may want to kind of go back and look at that again. Okay, so what are the blood vessels?

Because those are kind of what we don't see when we moved off the screen there. Well basically

they go from the arteries to the arterioles. So here's an artery right here. It's then

going to go to the arterioles and then it's going to go to the capillaries and then it's

going to go back to the venules and then it's going to go back to the veins. And so most

of the pressure is being handled by the arteries and the veins. And so the red is going to

be the arteries moving away from the heart and the blue is going to be the veins coming

back. One quick side note, blood is red. It's always red And some kids get confused because

they see diagrams like this and they think blood is blue and somehow if you somehow cut

yourself it turns from blue to red. That's just a silly story. It's just not true. So

I hope I didn't shatter too many dreams that you had. It's always red. And some people

say "Well look at my veins, they're blue." And I would say "'You're right, that's the

connective tissue in those veins but it's not the blood. The blood is red." Sometimes

it's really red, but it's red, it's red, it's red. Okay. So how do the arteries differ from

the veins? The arteries differ from the veins in a few ways. Number 1, they're not going

to be as strong, there's not as much connective tissue around it. But they also have valves

in them. Because once that blood has gone all the way down to the bottom, down here

to your feet, it has to get it's way all the way back to your heart. We've lost a lot of

that pressure. And so as the blood flows up, we have veins, we have valves that are found

in the veins and so it will actually move up. And then it can't go back down again because

this closes. And so it's going to work it's way back up to the heart. And that's why if

you're on bed rest for example it's important that we move your body around because as you

move muscles you're actually helping to return that blood back to your heart. What is blood?

Well blood is made up of four things essentially. We've got red blood cells. Those are carrying

the oxygen. Those are carrying the oxygen around your body. We also have the plasma.

Plasma's going to be the liquid portion. It has a lot of the nutrients in it, but it's

also going to carry that carbon dioxide as bicarbonate. We have white blood cells. White

blood cells are going to fight infection. And then finally we have platelets. Platelets

are important in blood clotting so if you get a cut the platelets will form almost a

lattice across that cut and eventually you'll have formation of a scab. And so if you look

at blood, blood is going to look like this but if we let it settle out what you're going

to get is those red blood cells are going to be down here and then we're going to have

the other things continue throughout that whole of the blood, like plasma. Okay. Your

heart goes through what's called a cardiac cycle. Cardiac cycle is going to have two

parts to it. It has diastole and systole. Diastole means filling and systole means pumping.

And so let's say you were to take a turkey baster. So a turkey baster looks kind of like

this. Like that. And so basically what you do is you squeeze the bulb down here and so

that's like systole. You're squeezing it and the liquid would flow out. And then when you

relax it, it's going to suck that fluid back into it. And so if you're basting a turkey

that works great. So how does a heart work? Well it's going to have a systole as well

when it contracts and then it's going to have a diastole where it's relaxing. And so we

have to time it as well. Because if the whole thing were to contract that wouldn't work.

And so basically what you have is you have systole up here, so you're contracting the

atrium and that pushes it down into your ventricle. You're ventricle at that point would be relaxed

and then as we pump our ventricle it's going to move it back in this direction and we're

going to have relaxation of the atrium so we can get new blood flowing into it. And

so what you hear in a heart is that lub dub, lub dub, lub dub, lub dub. And why do you

hear that? Well you're getting that contraction of the atrium. And then they relax. And then

contraction of the ventricle. And the ventricle is more powerful because it has to push it

into the lungs or it has to push it to rest of the body. And so it's going to be way more

muscle that we have down here in the ventricles than we do in the heart. And we're going to

have way more on the left side because that has to push it all the way around the whole

body. So timing is important as well. So basically you have this sinoatrial node, or the SA node,

and what it's going to do is this is where the heart contraction is going to start. So

you can imagine here is our heart, let me draw it in so you can kind of look at it.

So we've got that. We've got our atriums. And then we've got our ventricles here. So

we've got our atriums and then we have our ventricles here. So basically what's going

to happen is you're going to start the contraction at the top of the heart and it's going to

squeeze the atrium shut, so we're going to get a flow of electricity in contraction,

pushing it down like that. But then what happens is that electrical signal will go all the

way down here to the apex of the heart and then we're going to get it flowing in the

other direction. So now we have that flow going up to the ventricle because we want

to move that blood remember from the atrium to the ventricle. And then the ventricle either

out to the pulmonary artery or out to the aorta. So it goes to rest of the body. And

so that's an electrical signal that does that. Now your heart, as I said at the beginning,

continues to beat your whole life. But it's a muscle and it needs oxygen and it needs

nutrients as well. So how does it get those? Well we have what are called coronary arteries

that are on the outside of your heart. And those coronary arteries are going to serve

all of the muscle inside the heart. And if we ever have a blockage inside one of those,

what's that going to do? Well, we're not going to get nutrients and oxygen to that part of

the body and so that part of the body is going to die. It's not going to be able to do it's

job. An so what is a heart attack? A heart attack is simply when you have blockage in

the vessels that serve the heart. And so the heart muscle can die. And that's why it's

super important that we take care of our heart. We keep our vessels very very clean because

we need our heart to beat our whole life. And I hope that's helpful.