00:01
So when you first sat down
to learn about the thorax,
I'm guessing your
first thought was,
"Hey, I'm going to learn about
the lungs and the heart."
Iit might be a little surprise,
we're just now getting to the lungs.
00:11
Probably even more surprised
that we're going to do it
in a single session as opposed
to four or five for the heart.
00:16
That's because the real
complicated stuff in the lung
is occurring microscopically.
00:21
The micro anatomy, the histology
is really the complicated part
where the gas exchange takes place.
00:27
The gross anatomy
is actually not too bad.
00:30
So we're really going
to see the overall
shape and direction
and relations of things.
00:36
And we're going to start with
the left lung, from a lateral view.
00:41
The first thing we're going to
point out is the pointedness.
00:44
If we look superiorly, we see
that there's sort of a vague point
to the lung called the apex.
00:50
Conversely, at the bottom or the
inferior portion, it's much broader.
00:55
And that part we call the base.
00:58
We have an upper lobe,
that's not just more
superior than the other lobe,
but it's also a
little more anterior.
01:05
And it has a little tiny
special part called the lingula.
01:10
That we'll see later
is the portion of the upper lobe
that sits right over
the anterior aspect of the heart.
01:18
And then the other lobe
is the lower lobe.
01:20
And despite the name,
it's not just somewhat lower,
but it's also a little bit more
posterior than the upper lobe.
01:28
And that's because the gap or
fissure that separates the two,
it's running diagonally. In fact,
it's called the oblique fissure.
01:37
If we swing around to the right,
again, from a lateral view,
we can see a pointy apex superiorly
and a broad base inferiorly.
01:46
We still have an upper lobe,
and we still have a lower lobe.
01:51
And we still have
an oblique fissure
running along the front
of the lower lobe.
01:57
But on the right side,
we have an extra lobe.
01:59
We have the middle lobe.
02:01
And this middle lobe is
separated from the upper lobe
by a different fissure
called the horizontal fissure
because it's running
less diagonally.
02:11
Now, let's take some medial views.
02:13
So we'll go back to the left lung
and look from a medial perspective.
02:18
And we're going to focus on really
the only thing there is to see here,
which is that central depression
or hilum of the lung.
02:25
In three key structures here.
02:28
The first one is the left bronchus.
02:32
And we see superior to the
bronchus is the pulmonary artery.
02:38
Inferior is where we find
the pulmonary veins.
02:43
In order to get a sense
of the relationships
of the lung to what's nearby,
we've kind of put in these
little grooves or impressions
for structures that are resting
right up against the left lung.
02:55
So, the first one we
see here is pretty big.
02:58
And that's because on the left
side, we have a group for the aorta.
03:03
We have the arch becoming
the descending aorta here.
03:07
We also have grooves for
some branches of the aorta.
03:11
Namely, we have
the left subclavian artery here.
03:15
And we also have corresponding
veins in this area.
03:18
For example, we have
the left brachiocephalic vein.
03:22
And more centrally, we have
this long tube, the esophagus.
03:27
But the biggest impression
here is for the heart.
03:30
And so that's
the cardiac impression.
03:32
And that's because
the heart is mostly off
to the left side
of the thoracic cavity.
03:36
We'll swing around to the right,
and look at the right lung
from a medial view.
03:40
Again, focusing in on the hilum
and the three key structures.
03:45
And we're going to
start with the bronchus.
03:47
And this is a subtle but
important difference.
03:50
Here on the right side,
the pulmonary artery sits
anterior to the bronchus.
03:56
And it may not seem
like a big deal now.
03:58
But if you were to start
learning about
congenital heart diseases,
for example,
you really want to know
the relationship
of the bronchus to the artery
And the way to remember that,
is Right Anterior Left Superior.
04:13
And what that means
is on the right side,
the artery is anterior
to the bronchus,
and on the left side, it's superior.
04:22
So, R-A-L-S, or RALS is the acronym.
04:27
That sounds like a made up word,
but it's kind of isn't
because RALS, R-A-L-S
is actually the sound for crackles
when you auscultate lung sounds.
04:36
So it's at least
thematically linked.
04:39
Regardless of the
orientation of the artery
to the bronchus on either side,
the inferior most structures are
going to be the pulmonary veins.
04:48
If we put in those grooves or
impressions on the right side,
because of the asymmetry
going on in the mediastinum,
we're going to see
different structures here.
04:57
So we're gonna see
more venous structures.
05:00
For example, we're going to see
the group for the SVC,
or the superior vena cava
and the right brachiocephalic vein.
05:08
This is also the side that
we're going to see the azygos vein.
05:13
And of course,
we're going to have a little bit
of a groove for the inferior vena
cava before it reaches the heart.
05:21
We do have a little bit
of an artery here,
the right subclavian artery, but
not a lot of arterial structures.
05:28
Down the midline, and the longest
tube here is the esophagus.
05:33
There is a slight impression
here for the heart.
05:36
But because most
of the hearts off to the left,
it's a lot shallower
than it is on the right.
05:42
The trachea and bronchi, already
covered in separate section.
05:45
But now that we've mentioned
some of the asymmetry,
namely the different number of
lobes and the presence of the heart.
05:52
Hopefully,
if you were to go back
and look at that trachea and bronchi
section again,
you would understand why the
asymmetry is what it is there.
06:01
So now we're going to talk about
lymphatic drainage of the lungs.
06:04
Lymphatic drainage is
important for a lot of reasons.
06:07
And one of the reasons
it's important to lungs
is because the lungs are a
common sight of lung cancer.
06:13
And as we learned in
the breast section,
lymph nodes are an
important part of staging
how far a cancer has spread.
06:22
Cancers in the lung can spread
via the blood or the lymphatics.
06:26
However, the lymphatics are
rarely confined to certain areas,
because lymphatic vessels and
their associated lymph nodes
have to exit the hilum.
06:36
We have a predetermined path,
so we know exactly where
these lymph nodes draining
the lungs are going to occur.
06:45
Intrapulmonary lymph nodes
that are draining
intrapulmonary lymphatic vessels.
06:50
And then when we reach
the outside border,
where we hit the bronchus,
we have the bronchopulmonary
or hilar lymph nodes.
07:00
If we keep going,
we're going to hit the
carinal lymph nodes at the carina.
07:05
The tracheal bronchial nodes
at that junction
of the trachea and bronchus,
all the way up to the
paratracheal nodes.
07:13
And for the most part,
these lymphatics are going to drain
on the right side into
the right lymphatic duct
and on the left side
into the thoracic duct.
07:22
But some of these upper ones,
some of these paratracheal and
tracheal bronchial lymphatics
might drain into
their own special duct
called the bronchomediastinal
lymph duct,
which will actually drain
into the venous system directly.