So what you're looking
at is basically kind of a mechanistic way
of thinking about the heart, almost as if it's
a couple of pumps with pipes attached
to the pumps. And in a way, that's not a bad
way to think about the heart. In fact, we're going to kind
of move through this diagram. And I realize it looks
a little bit scary. But once I start
labeling stuff, you'll start seeing that it's actually
not as bad as it seems. So let's get started in the
upper part of the heart. The right atrium is right
there, and then blood goes down into the
right ventricle. And then on the
other side, I'm going to label the last two
chambers, the left atrium and the left ventricle. And we're going to actually
follow the path of blood after it leaves the
right ventricle. We're going to start our journey
here at the right ventricle. So what's the first thing
that kind of comes across? Well, blood leaves
the right ventricle, goes through a valve. And after, on the
other side, you've got this area right here. And I've drawn it as
one tube with no split, and this is the pulmonary trunk. So blood is headed
towards the lungs, going first through the trunk. And of course, after the trunk
there's a left and right. So I'll write that up here. The pulmonary arteries are next. And remember, I
call them arteries because they're going
away from the heart. And there are two arteries. So pulmonary arteries, left
and right pulmonary arteries. And that's why you
see two things here. One here, and you see one here. And those are basically tubes. So it's going from
the pulmonary trunk. It's splitting into
one of the two tubes. And now I'm drawing the
left and right lung up top. And of course, you know
that the lungs are actually not going to look this way. So this is not
anatomically correct. But this is not, as I
said in the beginning, a bad way of thinking about it. So blood goes through
the lungs and then comes out on the other side. And there we're
going to talk about left and right pulmonary veins. And actually, here I'm going
to make the point that there aren't just two pulmonary
veins, one for each lung. Actually, there are
usually more than that. And so when I draw
this, too, I really want you to just think
of the two sides, veins coming from both sides. But the actual number could be
a few pulmonary veins in total. The pulmonary veins drain blood,
then, into the left atrium, right? So now we're on the
other side of the heart. And for the moment, I'm going to
kind of pause the journey here. So we've gone from the right
ventricle, around to the lungs, back again in the left atrium. And this is kind of the
first part of our journey. And this part of the
journey is called the pulmonary circulation. I'm actually just going
to write that here. Pulmonary circulation. So the fact that this part is
going-- starting from the heart and going back to the
heart is one circuit, and our heart actually
has two circuits. But I want to point out
the circuits one at a time, and we've already kind
of completed one circuit. So I'm going to
take some blue paint to indicate deoxygenated
blood, or blood without oxygen. I'm going to paint
in how it would look. And actually, it stopped
there because my arrows. But you can actually see now the
deoxygenated blood kind of goes from the right ventricle,
through the pulmonary trunk, through the arteries, and
into the left and right lung. And once it's there,
it's going to kind of mix in with the capillaries. And it's going to
start getting oxygen, and then it's going to
come out on the other side in the pulmonary veins. And it's again stopped
a little bit there, but I can fill it in. And the pulmonary
veins are going to deliver that oxygenated
blood to the left atrium. So what you see kind
of colored in now is the pulmonary circulation. That's the first
part of our circuit. But let's now keep
going and now talk about the second part of the
circulatory system, which is the systemic circulation. So now the journey starts
with the left ventricle, so let me start there. So for the systemic
circulation, I'm going to start the
left ventricle. And it's going to go
around to the body, right? The body is kind
of the thing that's going to be receiving
all of the blood. And when I say body, I
really mean lots of things. I mean things like
the brain, so it could be an organ like
the brain or the liver. It could also be maybe
things like bones, if you have bones
in your fingers. Could be the toes. Could be any part of your body
that you can think of, right? So all these different
organs and tissues are going to be getting blood
from the left ventricle. It's going to be going initially
through a giant vessel. This vessel I'm going to label
it say, here, as the aorta. So this large
vessel is the aorta. And of course, it
branches and splits. And I haven't shown
all the branches that come off the aorta. But there are
many, many of them. It goes to the various
tissues and organs, and then it comes back
out on the other side. And at the end, kind
of somewhere up here, it's going to go back
to the right atrium. And it generally travels through
two major kind of vessels. One is the inferior,
and the other is the superior,
meaning lower and upper. And they're both
called vena cava. So superior vena cava
and inferior vena cava. I'll just write that here. So these are the two major veins
that are bringing back blood from all the different
parts of the body. And so now you've actually
seen the second circulation, because it all ends
at the right atrium. And this is the
systemic circulation. I'm going to write
systemic circulation here. So now you can see that
the heart is really two different systems-- or let's
say two different circuits, rather. And the first one, the
pulmonary circulation, is really kind of relying on
the right ventricle as the pump. And the second one is relying on
the left ventricle as the pump. And actually, now that you've
seen it, I can now color it in. There it would kind of
deliver all the blood to the various organs,
and then the organs would use up the oxygen. So let me show it kind of
now going back to blue just to indicate deoxygenated
blood, and it goes back to the right atrium
as deoxygenated blood. So this is kind of how
we sometimes see it. And again, this doesn't
show you or give you an appreciation for
the anatomy exactly, where things branch
off and where the different names make sense. But you get a kind of
overall feel for the fact that we have two
different circulations, and you can see
where the blood is going for the two
different circuits. Now, when you look
at this picture, you could say, well,
OK, I guess you can see where all the different
tissues are getting the blood. Basically sounds
like everything is coming from the oxygenated
blood coming out of the left ventricle. But some tissues always kind
of trip people up or kind of spark a question,
and I'm just going to kind of try to target
a couple of the tissues that I think people sometimes
might have questions about. And one of them-- wouldn't
really call it a tissue, but you could definitely
call it a cell type. It's the RBC, and RBC just
stands for red blood cell. So people sometimes
wonder if the red blood cells are carrying blood
to other parts of the body, then how do they
themselves get oxygen? Do they just kind of use
up some of the oxygen that they're carrying,
or what exactly? And to answer this
question, I would have to remind you that a
red blood cell basically looks a little bit like
this in cross-section. And it doesn't have
any mitochondria. No mitochondria. So it has no mitochondria. And remember, mitochondria are
these tiny little organelles inside of cells that
are using oxygen. So if it has no
mitochondria, then it is not really using oxygen. So it's not using oxygen. And really, these cells--
we call them cells, and they are in many
senses of the word. But they don't really
have mitochondria. They also don't have a nucleus. I mean, these are, literally,
these amazingly designed cells that are made for the purpose
of carrying around oxygen to the body, because
they literally are bags of hemoglobin. So just remember, red blood
cells don't really need oxygen. They simply carry it around. Another tissue or organ that
makes people kind of wonder is the heart. The heart is pumping
all the blood around. But does it actually
get oxygen from vessels that are in the
pulmonary circulation or from the systemic
circulation or what? And here, the short answer
is systemic circulation. That's kind of the quick answer. And let me actually
show you where the blood vessels come from. These are called
coronary vessels. I'll just write the
word coronary here, coronary vessels. So coronary artery and vein. And these coronary
vessels, they actually come right off the
aorta here and here. So they kind of come off
of the aorta right away. They're the first branches
off the aorta, actually. So the first branches
go and serve the heart, so it's kind of the first to
get systemic circulation blood. And the veins actually
drain into a spot directly into the right
atrium, so there's actually a little spot right there
that they drain into. So the blood from the arterial
side is coming from the aorta. And on the venous
side, it's actually not even dumping into the inferior
or superior vena cava. Kind of a little
known fact, it's going directly into
the right atrium. And finally, kind of a
tricky one, but the lungs. Where do the lungs
get their oxygen from? And this is, I say, tricky. And I kind of saved
this for last, because there are
actually blood vessels. And again, don't worry so much
about the anatomy in terms of where is it coming
off of exactly? But it's coming off of
the systemic circulation, and you've got a vessel
going to the right lung. Let's say something like that. And you've got
another vessel going-- I'll just draw it
kind of going-- to the left lung like that. So you've got a
couple of arteries that are branching
off, and these are also part of the systemic
circulation. And these are called
the bronchial arteries. And these bronchial
arteries bring then really wonderful oxygenated
blood, right? These are the
bronchial arteries. And you might say, well,
that wasn't so difficult. I'll say bronchial vessels,
because there are also some veins coming off. Actually, let me draw
the veins now for you, so you can see how
those kind of end up. And these veins, they come
from, of course, the right lung. And they actually end
up dumping in here. You can't really
show blue on blue, but just trust they go there. And you've got another vein
from the other lung, kind of following a parallel path and
going into the veins as well. And so they don't dump
necessarily directly into the inferior or
superior vena cava, but I just want
to show that they go into the venous side on
the systemic circulation. So if that was it, that
would be really simple. But actually, lungs are kind
of interesting in the sense that there is a lot
of mixing going on. So you've got pulmonary
arteries carrying blood. You've got bronchial
arteries carrying blood, and that blood mixes. And then you've got--
at the capillaries, you've got some blood
kind of from both places, the pulmonary
circulation and blood from the systemic
circulation again mixing. And then on the other side,
where the veins are bringing blood back to the heart, most
of the blood-- as it turns out, most of the blood
actually goes this way, into the pulmonary veins. So even though you have
bronchial arteries bringing blood in-- that
would be right here-- you only have bronchial
arteries bringing blood in, a lot of that
blood ends up going into the pulmonary circulation. So that's kind of an interesting
fact, that not as much goes this way directly into
that systemic circulation. So it's kind of a tricky
thing to keep in mind. But the lungs, then,
technically really are getting blood both from
the systemic circulation, but also they're
kind of mixing blood. And they're mixing blood with
the pulmonary circulation. We'll talk a little bit more
about this in another video. I don't want you to feel like
this kind of got too confusing. But I just want you to be aware
that there is mixing going on in the lungs with the systemic
and pulmonary circulation, kind of a neat organ in that sense.
