Hi. It's Mr. Andersen and I was just checking my pulse to make sure that
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.