00:01
Let's continue our discussion
of the respiratory system
by talking about the
lower respiratory tract.
00:07
We mentioned last time that
the lower respiratory tract
picks up after the larynx
and begins with the trachea.
00:16
The larynx, which is made of
cartilage connects to the trachea,
which is also made of cartilage.
00:22
Although this cartilage doesn't
go all the way around the airway,
it's actually more of a C-shape,
with cartilage missing at
the posterior portions.
00:32
It then terminates at
something called the carina
where it becomes the right main
bronchus and the left main bronchus.
00:42
And you see that the
left main bronchus
branches at a different angle
than the right main bronchus.
00:48
And that's because of
the presence of the heart
in the left side of the chest.
00:54
Here we see how the lungs sit
in relationship to things like
the trachea and the heart.
01:00
We have the trachea, again,
coming down from the larynx,
dividing into bronchi
that supply the lungs,
one on the right,
and one on the left.
01:11
The right lung can be
further divided into lobes.
01:15
We have a superior or upper lobe,
a middle lobe and an
inferior or lower lobe.
01:24
On the left, however,
we typically only have two.
01:27
We have a superior upper lobe,
and an inferior or lower lobe.
01:35
Here we can see the right
and left main bronchus
entering the right
and lung respectively.
01:41
We can also see by removing some
of the substance of the lungs,
just how much branching
there is occurring
in association with the
right and left pulmonary arteries.
01:53
And that's happening both at a
macroscopic and microscopic level
in order to help achieve
gas exchange.
01:59
And we'll see that
a little bit later.
02:02
We also find veins.
The right and left pulmonary veins
are merging into
larger and larger ones
until eventually there's a pair on
each side emerging from the lung.
02:15
And where these
things emerge or enter
is an opening in the lung
called the hilum.
02:21
And hilum is a term you
see in a lot of organs.
02:25
A hilum is an area where vessels
and other things
in this case, the bronchus
enter along that otherwise doesn't
have any other connections.
02:36
So here we see the
right hilum of the lung,
where the right pulmonary
artery is entering.
02:44
And we also see
the pulmonary veins.
02:47
And here we have the left hilum with
the left pulmonary artery in veins.
02:53
The space between lungs,
something called the mediastinum
and contains a lot of
important structures.
02:59
Most posteriorly,
we have the esophagus,
which is really just carrying
food through the thorax
down to the abdomen where it's
going to empty into the stomach.
03:08
Just anterior to the
esophagus, we have the trachea.
03:14
We also have coming off of the
heart which has been removed here,
the aortic arch, which ultimately
becomes the descending aorta
and will eventually pass down
into the abdomen as well.
03:26
Here we see the left lung
from a lateral point of view.
03:31
And we see that it
vaguely has a pointed area
towards the top called the apex.
03:38
And at the bottom or the
inferior end, it's much broader,
and we call that portion
of the lung, the base.
03:46
Again, we have an
upper or superior lobe
and a lower or inferior lobe.
03:52
And those two lobes are separated by
something called an oblique fissure.
03:58
And this fissure is just
what the name sounds like
it's oblique or diagonal.
04:05
There's also a little
bit of the upper lobe
that sits directly over the heart
and it's a very thin portion.
04:12
And that thin portion
somewhat resembles a tongue
hence the term lingula
because lingula
refers to the tongue.
04:21
If we were to look from
a medial point of view,
we would see a little bit of a gap
in the lung called again the hilum,
where structures can enter an exit.
04:31
And the case of the left lung,
we have the pulmonary artery sitting
just superior to the bronchus,
and then most inferiorly
we have the pulmonary veins.
04:44
Here we go back to
the lateral view,
but this time we look
at the right lung.
04:49
Again, the pointed area
at the top is called the apex
and the broad area at the
bottom is called the base.
04:55
And we still have
an upper lobe and a lower lobe.
04:59
And they're also separated
by an oblique fissure,
just as in the left,
but on the right, we have an
extra load called the middle lobe.
05:08
And it's separated
from the upper lobe
by a more horizontally
oriented fissure
called the horizontal fissure.
05:15
And this makes sense that we have
room for an extra lobe on the right,
because the heart is occupying
space on the left side of the chest.
05:25
Again, if we switch
back to a medial view,
we find the hilum where
things enter and exit.
05:30
And this case on the right side,
the pulmonary artery sits
anterior to the bronchus.
05:37
But again, the veins still
sit inferior to both.
05:43
So this brings us to the concept
of pulmonary circulation.
05:47
It's very different than
systemic circulation,
which is essentially all
the rest of our circulation.
05:53
And pulmonary circulation starts
with the pumping action
of the right ventricle.
05:58
That's going to pump blood out
through the pulmonary arteries,
where it can get
oxygenated in the lungs
and come back as the pulmonary
vein into the left atrium.
06:13
And from there,
that reservoir of oxygenated blood
can be used for
systemic circulation.
06:19
Now, this may be a
little confusing because
some of you probably have
always thought
that arteries carry oxygenated blood
and veins carry deoxygenated blood.
06:27
And that's because we typically
think of circulation as systemic
in which that is the case.
06:33
But arteries and veins
aren't defined by
whether they carry oxygenated
or deoxygenated blood.
06:39
They're defined by whether
they're going away from the heart,
or coming toward the heart.
06:44
So an artery is an artery as long
as it's going away from the heart.
06:48
In this case, the pulmonary arteries
are going away from the heart,
but they are carrying
deoxygenated blood.