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.