Arteries vs. veins - what's the difference Video Lecture - Class 10

OK.
Let's talk about the
arteries and the veins.
And I'm actually going to
talk about both of them
simultaneously, because
there's some really interesting
differences I want to
point out between the two.
We know that they're
both vessels.
But there's some really
important differences
between how they work
and what they do.
So this is your heart,
and coming off your heart
is the aorta.
And before this video,
I've been drawing the aorta
quite differently kind
of showing its branches.
And here I'm showing it
kind of stretched out.
And I'll show a few
of the branches.
But really, the
point of the drawing
is not to make it
anatomically correct.
You can tell it definitely
is not anatomically correct,
because that wouldn't make
any sense at all, to have
blood going off to one side.
But really, I want to show
you a concept in this video.
A few concepts, actually.
So here we have,
let's say, the veins.
And I'm going to stretch
that out as well,
and let's imagine
that all of the veins
are dumping into this
one final vein that
gets back to the heart.
So I'll draw the branches
kind of coming into the vein
here and here.
And we know that the
arteries and the veins
are trying to get blood
out to the capillaries.
So let me just show you what
a zoomed-in version might
look like of the capillaries.
So we've got, let's say, some
capillaries here, and maybe
some here and here.
And you know, of
course, in real life,
you don't have three sets
of capillary beds, which
is what I'm drawing here.
But really, you have
thousands and thousands.
And let's not forget that
these capillaries are basically
found in different
parts of the body.
So you might have, for example,
a bone and some capillaries
in the bone.
This second capillary might
be going to your face,
let's say even
specifically your nose.
And this third
capillary bed, that
might be going down
to your foot so
that you have
blood in your foot.
So you have different
parts of the body
all getting capillaries.
And the blood is going
to start at the heart,
go to the capillaries
through the arteries
and then return through
all of those veins.
And we've lumped it together.
And what I want to show you now
is that this very, very simply
is the systemic circulation.
Now, of course, you
know that there's also
the pulmonary circulation.
So what does that look like?
Let me draw that out here.
So pulmonary you
know means lungs.
And I've shown you previously,
in another video, that there
is blood going to these lungs
in a very low-pressure system.
So we talked previously about
low-pressure and high-pressure
systems, and now just
remember that this
is kind of how it gets there.
You have the deoxygenated
blood or the blood
in the blue vessels kind
of going up like that,
and this would be
the pulmonary artery.
I'll write ART for artery.
And we have the pulmonary
vein bringing that blood
back to the heart
with oxygen in it.
So that's your
pulmonary circulation.
So you have pulmonary
circulation,
and you have the
systemic circulation.
And I'll get back to why I
drew the pulmonary artery
in blue and pulmonary vein
in red in just one second.
Let's just put that on
the side for a moment,
and let's get into
exactly how to think
about arteries and
veins in general.
So in general, I
think of arteries
as taking blood
away from the heart.
That's probably the
easiest and most clear way
of figuring out what
an artery is exactly.
So arteries are taking
blood away from the heart.
Let me just draw a
little arrow here.
And veins are
bringing blood back.
And so this becomes our first
point, point number one.
And this is a point of
difference between the two
of them, is the
direction of flow.
And even if you look at
the pulmonary system,
you can see that remains true,
that the arteries are taking
blood away and the vein is
bringing the blood back.
Point number two-- now,
you see that the arteries
are drawn in red,
for the most part.
And so usually arteries
have oxygenated blood
that they're bringing
out to the tissues,
and then the veins carry
the deoxygenated blood
that they're bringing
back from the tissues.
So point number two is
really about the color,
and so let me
write that in here.
So this would be like a little
red blood cell with hemoglobin
in it, and this is a
little red blood cell.
Still called a red
blood cell even
though its color is more
blue, but it's still
got hemoglobin in it.
But the hemoglobin
down here actually
doesn't have any oxygen
left, and so the color
looks quite different.
So the color of arterial
blood is usually
red because of the
fact that oxygen
is bound to the hemoglobin.
And less oxygen is bound
on the venous side,
so that's why it turns blue.
Now, I want to just put
a little star there,
because that's not always true.
And you can see where clearly
it's not true is over here.
Let me star the pulmonary
circulation, where
you can see that the pulmonary
artery and vein-- I'll
star that just to really
emphasize the point--
are actually the
reverse of what I just
said, because the pulmonary
artery is actually going
to carry the deoxygenated blood.
And the pulmonary vein is
carrying the oxygenated blood.
So clearly, that's the
reverse of what I just said.
But that is one exception
to the general rule, which
is that arteries
definitely look red
and veins generally look blue.
So those are two
points of differences
between the arteries and veins.
Let's keep going.
So now you know that
arteries are high pressure,
because the heart is
pumping the blood out.
And it's going to be under
very, very high pressure.
And so I kind of
think of the arteries
as being like a river,
a fast-flowing river.
So you can think of this as
fast flowing, high pressure.
So that is the third difference.
So this is a
high-pressure system.
Third difference is that
it's a high-pressure system.
In fact, maybe I'll
even emphasize the point
by writing the word very
large, high pressure.
And actually, the other thing
we think about with arteries
is that there's not so much
volume in the arteries.
Let's say I froze
time and I asked
you to try to figure out where
all the blood was located.
Not too much of it
is in the arteries.
So it's actually a
very low-volume system.
I'll write volume very small.
And the veins are the opposite.
They're kind of a
large-volume system,
and they have really
kind of low pressures.
So I'll write pressure
very small over here.
And if you actually
figured out what percent
is where in terms of the
amount of blood, about 5%
of the blood at any point in
time would be in the heart.
And let's say about 5%
would be in the capillaries,
and then about 10% or so
would be in the lungs.
So what are we up to now?
We're at 5 and 5 is 10.
10 plus 10 is 20.
And then we have another about
15% percent in the arteries,
so about 15%.
So that's actually
not too much blood.
And so the remaining
65% of the blood
is actually in the veins
at any point in time.
So that's remarkable.
About 2/3 of the blood
at any point in time
is actually sitting in
all the veins combined.
And so the way I've drawn it
is really not really the best
way to draw it.
I should really
erase this and really
redraw this to make
it much more accurate.
It should look a
lot more like this,
like a big giant lake of blood.
And so this is actually how
to think about the veins.
It's actually a very,
very low-pressure
but high-volume system.
So that might be the third point
I'll bring up on the vein side,
is that it's a
high-volume system.
Now, we've talked about
the direction of flow.
We've talked about the fact that
one side carries more oxygen
than the other.
And we've also
talked about the fact
that the arteries are a
high-pressure, low-volume
system.
And the veins are a high-volume,
low-pressure system.
So what are some
other differences?
So one other difference
is that in the arteries,
you actually don't
have any valves.
Now, I don't know how to label
that to make it super clear.
But let me just find
some sort of open spot
here and write a number four.
There are no valves in
that arterial system.
Whereas, on the venous side,
you actually do have valves.
You have these valves
that come together.
Let me make it very clear by
making the two sides touch.
And the blood goes
through like that,
so you have these valves
that keep the blood going
in the right direction.
So that would be
the fourth point
of difference between the
two, so you have these valves.
And you might get confused
because you think, well,
doesn't the heart
also have valves?
And it does.
The heart also has valves.
But the veins have a
different type of valve,
and that's actually to
keep the blood flowing
in the right direction.
You can imagine that
you probably don't even
need that on the arterial
side, because the pressures are
so high that the blood
is forced to go one way.
Whereas, in the veins, because
it's kind of like a giant lake,
water can kind of swirl
around and around and around.
And so it's helpful
to have valves keeping
it going in the right direction.
So that's a fourth
point of difference.
So now think about
the fact that you
might have a break in
the arterial system.
So let's say that
you have an accident
and you cut a big
artery, let's say.
What would it look like?
So if you have a
break right here,
you would actually have
like a fountain of blood
coming out right there, because
it's under such high pressure
that it's just
going to spew out.
And so this is basically what
it looks like when you actually
cut an artery, again,
because of the fact
that it's under
such high pressure.
And now on the venous
side, or on the vein side,
if you have a break, it
looks really different,
because if you have,
let's say, a break right
here, you'd actually get
kind of a pool of blood
just locally before it clots
off, because, again, you
have very low pressure.
So it's just going to
kind of quietly pool,
and you might get a
bruise right there.
But it certainly won't look
like a fountain of blood.
And so that's actually
another final point
of difference, which
really gets back
to the high-pressure
system on the arterial side
and the high-volume,
low-pressure system
on the venous side.