Welcome to this lecture on Pulmonary Structures
This slide captures the learning objectives
that you should be able to answer
at the conclusion of this lecture.
First, describe the pleural membranes and
Describe the trachea, its wall composition
and bronchial branching pattern.
Compare and contrast the features of the right
and left lungs.
Describe the applied anatomy in performing
Describe the esophageal segments, constrictions
and the layers forming its wall.
Describe the locations of esophageal diverticula
and the relevance of Killian’s triangle.
And then we’ll summarize the key take-home
messages from this lecture.
Lastly, we’ll provide attribution for the
images that were used throughout this presentation.
Here is our body map and most of our attention
is going to be focused in the pleural cavities.
And then, we’ll also focus some of our attention
in the mediastinum
when we look at the esophagus and trachea, bronchi.
This particular slide represents the rationale
for talking about not only respiratory structures
such as the trachea, the bronchi and the lungs,
but also to include the esophagus.
What is interesting, developmentally, is that
the foregut derivatives will give rise not
only to GI structures, but will also give
rise to the pulmonary airways and the lungs.
So, if we take a look at this area here, we
are looking at the primitive foregut region
and here we see the development of the trachea
which then will lead to the development of
its branching pattern and then, more distally,
to the development of the lungs.
Here running posterior to the development
of the trachea would be the portion of the
foregut that will give rise to the esophagus,
the stomach and the proximal duodenum as well
as GI organs: the liver, its associated biliary
apparatus and then the pancreas.
This slide is demonstrating the concept of
the pleural membranes. Since the lungs reside
within their pleural cavities, we will have
investments of pleural membranes. So, we’ll
need to understand those membranes.
Here we’re looking at the right lung. Here
is the left lung. And then, lining the thoracic
cavity on either side, is this outer green
line. So, it’s just on the inner thoracic
wall. This is going to be your parietal pleura.
It similarly will be adhered to the inner
thoracic wall associated with the left pleural
cavity. If we follow this parietal pleural
membrane posteriorly, we will see that, at
the area where we have our vertebral column,
it will reflect back onto the surface of the
lung. This portion of the pleural membrane
that’s adherent to the surface of the lung
is now referred to as the visceral pleura.
There is a potential space between these two
pleural membranes and this potential space
represents the pleural cavity. In some cases,
excessive fluid, it may be blood or other
types of fluid that will excessively accumulate
within the pleural cavity converting the potential
space then into a fluid-occupied space.
This slide depicts the parietal pleural membrane
and its subdivisions. The subdivisions of
the parietal pleura are going to be named
according to the anatomic relationship of
each one. So, let’s take a look at those
Here, we can see the cut edge of the parietal
pleura associated with the right pleural cavity
and then over here we see the cut edge of
the parietal pleura that’s associated with
the left pleural cavity.
Most of the parietal pleura is going to have
a relationship to the vertebral column and
the rib cage. That then will be referred to
as the costovertebral pleura
or simply the costal pleura.
If we take a look, we also have the parietal
pleura that will cover the superior surface
of the left dome of the diaphragm along here
and then ascend up. Similarly, on the right
side, we have a portion of the parietal pleura
that’s associated with the right dome of
the diaphragm. This, then, is referred to
as the diaphragmatic pleura.
We will also have pleura that extends up and
over the apex of each lung up into the cervical
region, the inferior part of the neck. This
will be termed the cervical parietal pleura.
And then lastly, we’ll have parietal pleura
associated with each lung that will face the
mediastinum. And this would be referred to
as your mediastinal pleura.
When we think about the pleural membranes
and where they have points of reflection anatomically,
these points of reflection of the parietal
pleura will create various types of recesses
that are associated with the pleural cavities.
We have costal-diaphragmatic recesses associated
with the lungs, we have costal-mediastinal
recesses associated with each of the lungs
and we have vertebral mediastinal recesses
associated with the lungs.
The first two recesses are depicted, are illustrated
on this image. And so, the first one is a
fairly significant recess that projects inferiorly
and this is going to be the costodiaphragmatic recess.
Here we have the costal pleura and then, at
this point, it reflects onto the surface of
the diaphragm, becoming the diaphragmatic
pleura. And so, this area here is the costodiaphragmatic
recess. This represents a potential space
and may, in some cases, accumulate fluid.
We have the same costodiaphragmatic recess
that’s situated here on the left side as well.
The costomediastinal recess is along in through
here with the right lung.
We also have one on the left side.
This represents the point where the costoparietal
pleura is going to bend
and become the mediastinal parietal pleura.
The next slide will demonstrate the vertebral
mediastinal recesses. And that can be seen
along here. Again, the left side of the image
represents the right lung and here we have
the pleura reflecting in this area. This space
here is a potential space called the vertebral
mediastinal recess. And then we would have
a similar recess over here associated with
the other lung.
The next slide is going to demonstrate a procedure
called a thoracentesis. This type of procedure
is performed when there’s excessive fluid
accumulation in the pleural cavity. There
are several causes of excessive fluid accumulation.
The three primary causes would be heart failure,
lung infections as well as tumours.
When fluid becomes excessive, it has to be
removed from the pleural cavities and that’s
when a thoracentesis is performed. And then
let’s understand our applied anatomy to
be able to perform this procedure.
Here we’re in the mid-axillary line for
our point of reference. This happens to be
rib 9. This happens to be rib 10. So, we’re
operating within the 9th intercostal space.
Just inferior to rib 9, we have intercostal
structures, neurovascular structures, and
we want to avoid those so that we don’t
damage them. So, the best approach then is
to find the rib inferiorly here. And that
is going to be rib 10 and then to advance
the needle over its superior surface. And
you can see the tip of the needle has been
introduced into the costodiaphragmatic recess.
And then fluid can be removed once this needle
has entered that particular recess.
Now, let’s take a look at the trachea. And
what you’ll want to remember here will be
the vertebral levels where the trachea begins
and where it bifurcates.
The trachea is beginning at this point right
below the cricoid cartilage of the larynx,
which is here. And so, this is the initial
point of the trachea. It has a vertebral level
of C6. It then will travel distally and then
it’s bifurcating at this level. And this
will have a vertebral relationship between
T4 and T5. The distance travelled from C6
to T4 or T5 is only about 10 to 11 centimetres.
We’re only looking at a respiratory passageway
that is about 4 inches in overall length.
Not as long as we might think.
Along its length, you’ll see various cartilaginous
rings that are incomplete posteriorly and
the number of these cartilaginous rings is
anywhere from 16 upwards to 20.
Where the trachea bifurcates at its T4-T5
relationship, we can see a keel-like projection
at that level bifurcation. And that is shown
right in through here on the illustration.
That keel-like projection is called the carina.
And then you can see the right bronchus here
and you can see the left bronchus on the left
side of the carina.
What we’ll want to understand here is which
one of the bronchi is wider than the other
and which bronchus is more vertical than the
other. And in this case the answer to both
questions is the right bronchus.
The right bronchus is wider in diameter than
the left. The right bronchus is more vertical
than the left. The left bronchus comes off
at a more acute angle. We can utilize our
understanding of the characteristics of the
right bronchus when we think about aspiration
of a foreign object and the likelihood of
the bronchus then that will receive it. And
if you did follow a foreign object that’s
small enough, it has a greater likelihood
of entering the right bronchus.
The wall of the trachea is made up of layers
or strata. And those layers include the innermost
layer of the mucosa. External to that is the
submucosa. The third layer that’s even more
external is the cartilaginous/fibromuscular
layer. And then the outer layer or the coat
of the trachea is going to be the adventitia.
All four of those layers are depicted in this
slide. Here we have the mucosa and the portion
of the mucosa in direct contact with the air
moving though the lumen will have the epithelium
that lines the mucosa.
The submucosa is going to be characterized
by the presence of numerous glands that we see here.
The cartilaginous fibromuscular layer is demonstrated
here where we have the hyaline cartilage.
And then you can see posteriorly that the
rings of hyaline cartilage are incomplete
and the ends here of the rings are bridged
by fibromuscular components. So, here is the
collagenous component and then in red we have
the trachealis or muscular contribution to this region.
The outermost layer is your adventitia. That
is simply a connective-tissue coat.
There are various types of bronchi. So, let’s
describe the various divisions of the bronchi.
The first bronchi that form will be those
bronchi that divide where the trachea ends.
And these are primary bronchi: a right one
and a left one.
So, we have one primary bronchus for each lung.
Shortly after, each primary bronchus will
divide into secondary bronchi. And we can
see some secondary bronchi here and here and
here, for example. There are three secondary
bronchi to the right lung, two secondary bronchi
to the left lung. And secondary bronchi are
also known as lobar bronchi. The right lung,
as we’ll see shortly, has three lobes hence
it has to have three secondary or three lobar
bronchi. The left lung, normally, only has
two lobes and that is why we only have two
secondary or two lobar bronchi
associated with the left lung.
Each secondary bronchus will then divide into
tertiary segments. And we see numerous tertiary
segments in each one of these branching patterns.
Tertiary bronchi are also known as segmental
bronchi because tertiary bronchi are going
to supply each bronchopulmonary segment. Tertiary
bronchi will then undergo further successive
divisions. And there are many of these divisions
before they’ll finally lead to our system
of bronchioles. And the largest bronchiole
is referred to as a primary bronchiole.
The next slide that we’ll see will help
you understand the various structures that
are associated with the lungs in situ. And
those structures will be the lobes, fissures
and then two specific features that we see
associated with the left lung:
the cardiac notch and the lingula.
Here’s your right lung. It has two fissures.
One here: this is called the transverse fissure.
We also have a little bit shown here of the
oblique fissure. These two fissures help divide
the right lung into its three lobes: a superior
lobe, a middle lobe. And then we’re just
seeing a very small portion of a large inferior
lobe to the right lung.
The left lung only has one fissure. It too
is obliquely oriented and we just see kind
of the terminal aspect of that oblique fissure
here. That then means everything above the
oblique fissure belongs to the superior lobe
of the left lung. And then we’re seeing
just a little bit of a much larger inferior
lobe below the fissure.
Two structural features of the superior lobe
of the left lung would be the cardiac notch
that we see here. And you can see it receives
the heart as it projects to the left of the
midline. And then this tongue-like extension
here more inferiorly, but yet still associated
with the superior lobe is referred to as the
Each lung is going to present an apex, base
and surfaces. The apex of the lung, this is
the right lung, three lobes, the apex is shown
here. And then the base is opposite the apex
and is best demonstrated here. And we can
see that the base of the lung is concave because
of its relationship with the respective dome
of the diaphragm. So, the right lung with
its base will be related to the right dome
of the diaphragm. The concave surface of the
base of the left lung will be related to the
left dome of the diaphragm. And then the surfaces
of the lung: there are two. We have a more
extensive costal surface, which is everything
we see here. And then we’ll also be seeing
here more posteriorly.
So, it has relationships to the rib cage.
The mediastinal surface is this area here
and this is the surface of the lung that will
face the mediastinum.
Here we have the right lung in isolation and
we can better appreciate the two fissures
that are associated with the right lung as
well as the fact that the lung has three lobes.
Here is your transverse or horizontal fissure
and then here we can see more clearly the
extent of the oblique fissure. These two fissures
then will separate the right lung into a superior
lobe, a middle lobe and then this extensive
left lobe that we see here. And again the
lobes are supplied by secondary bronchi.
Here we’re looking at the left lung. It
only has one fissure: the oblique fissure.
And so, we see the extent of the oblique fissure
here. The area of lung above is the superior
lobe. The area of the lung below our oblique
fissure is going to be the left lobe.
And again, we can see the cardiac notch.
And you can see the lingula associated with that superior lobe.
On the following slide, you’ll be able to
understand the next concept about the lung
and that is the hilum of the lung. The hilum
represents the gateway into and out of the
lung. This gateway provides for the entry
of our respiratory passageways, the entry
of our pulmonary artery and its subsequent
branching pattern and then the exit of the
pulmonary veins that will conduct blood back
to the left atrium.
And so, if we take a look here, we have the
right lung above, its hilum is shown here.
Down below, we have the hilum that’s associated
with the left lung. And we can also see an
outline here of the pleura. And so, here the
pleura is approaching the lung surface itself
and then it’s going to spread out and adhere
to the lung and become the visceral pleura.
And where that reflection is happening below
the hilum, you’ll have this region here
of pleural membranes that constitutes what
is known as the pulmonary ligament.
In the left lung, its hilum will also have
a pulmonary ligament.
Now, within the hilum, we’ll have a relationship
of the airways to the vascular structures.
It’s going to be a bit different between
the right lung and the left lung.
In the hilum of the right lung, your airways
are located here in the posterior superior
aspect of your hilum. If you look anterior
to it, I can see the right pulmonary artery
entering the hilum and it will start to branch.
And then anterior to the artery and inferior
to the artery and airway, you have your two
pulmonary veins that are leaving the lung
to transport blood back to the left atrium.
In the left hilum, here is your airway posteriorly
located, but if you look here, the artery
is immediately above or superior to your airway.
And then your veins lie anterior and inferior
to those particular structures.
There is a mnemonic to help your remember
the anatomic relationship of the pulmonary
artery to the airway in each hilum. That mnemonic
is RALS. RALS stands for Right is Anterior
and Left is Superior. So, in the right hilum,
the artery is anterior to your airway and
in the left the artery is superior to your
The following slide will introduce you to
the concept of bronchopulmonary segments.
Bronchopulmonary segments are their own individual
anatomic unit. Each one is supplied by its
own respiratory passageway. Each one is supplied
by its own artery and also drains by its own
venous system. The bronchopulmonary segments
are also separated
from one another by connective-tissue septum.
As a consequence of these being their own
individual units, it is possible to surgically
resect or remove each one of these pieces
like you would a piece from a jigsaw puzzle.
The slide that you now see shows the various
bronchopulmonary segments in the right lung.
Each coloured region represents a separate
bronchopulmonary segment. Here we see the
numbering in a costal view. And then here
is the mediastinal view of the right lung.
And if you look at the numbering, you will
see that there are 10 bronchopulmonary segments
identified and this is what is normal in the
right lung. The left lung will typically have
two less bronchopulmonary segments. Thus,
we’re at 8. However, it may in some cases
have 9 or even 10.
Here is the left lung in its costal view.
And then, here’s the left lung in its mediastinal
view. And if you count the number of each
coloured segment here, you will see that there
are 9. But, if you look at the numbering system,
you’ll see that 10 is the maximum number
here. And it’s missing one, so this really
only shows 9, but that is within anatomic
variation. And again you can kind of appreciate
how you could surgically resect or remove
each one of these units. And so, if there’s
tumour involvement in two of the segments,
you then remove those surgically and then
you can leave the other bronchopulmonary segments
intact or in place. And each segment is supplied
by a tertiary or segmental bronchus.
The bronchi can be visualized, if necessary,
with bronchoscopy. And so, here we see a bronchoscopic
view. And we’re at the level where we can
actually see the segmental bronchi. So, here’s
a segmental or tertiary bronchus, here’s
another. Here’s one leading off here to
the left. Above at this branching point we see
some additional segmental or tertiary bronchi.
This particular slide is demonstrating an
area within a bronchopulmonary segment. This
region of tissue within the bronchopulmonary
segment is referred to as a pulmonary acinus.
Each pulmonary acinus is going to be fed by
a type of bronchiole called the terminal bronchiole.
Terminal bronchioles will branch from your
primary bronchioles. And so, this bronchiole
that we see here is a terminal bronchiole.
And the area defined within the region here
represents the pulmonary acinus. Within the
pulmonary acinus and even smaller divisions
upstream of this level, what you’ll see
is the pulmonary artery will follow the branching
pattern of the bronchus or the airway. In
this case, we’re at the level of the bronchioles.
Venous blood is going to be drained at
the periphery of this organizational unit, the acinus.
Now, let’s shift our focus to the esophagus.
And the first aspect about the esophagus is
the fact that it’s divided into three parts.
We have, and it’s best seen here in this
lateral view, the most superior portion of
the esophagus. This is the cervical part.
The most extensive part of the esophagus will
travel within the thoracic cavity and that
will be called the thoracic part. And then
the esophagus will pass through at the esophageal
hiatus within the diaphragm and become the
abdominal esophagus. And then the abdominal
esophagus will promptly empty into the cardiac
region of the stomach.
The esophagus has layers associated with its
wall. And those four layers are the mucosa,
submucosa, muscularis externa and then adventitia
throughout most of its length. But, within
the abdominal cavity, we’ll have a serosa
representing the outermost layer.
If we take a look at our illustration, here
is the mucosa. Here is the deepest layer here,
this thin red muscular membrane. And then
the most superficial layer, the mucosa, will
be the epithelium of the esophagus. Lying
deep to the mucosa is the submucosa. And then
we have a very thick muscularis externa with
two muscle layers: an inner circular layer
that we see here and then an outer longitudinal
layer shown here. And then the layer that’s
the outermost layer, this again is the tunica
adventitia: connective tissue. But, again,
if you’re looking at the abdominal part
of the esophagus, the connective tissue will
be limited most externally by a thin epithelial
layer becoming the serosa.
This slide depicts various constrictions that
can be seen along the length of the esophagus.
Three of them are identified on this illustration.
The uppermost point of constriction of the
esophagus is at this level. This represents
the upper esophageal sphincter region. And
this is at a junction between the pharynx
and the esophagus. So, we can refer to this
point of constriction as the pharyngo-esophageal
constriction. So, this is a natural constriction point.
Down more in the middle of the thoracic esophagus
we have a couple of other structures that
put pressure on the esophagus thus serving
as a combined point of constriction. We have
the aorta and the right primary bronchus.
And if we combine these two structures, this
represents the aorto-bronchial constriction.
And then the third and final constriction
is where the esophagus will pass through the
esophageal hiatus within the diaphragm. These
constrictions do have clinical significance.
The first example is during a procedure where
you may have to scope the stomach and look
for the presence of an ulcer or bleeding ulcer.
In order to do that, you have to advance the
endoscope through the esophagus and gently
pass the endoscope through these various points
of constriction. If one is too aggressive
with the advancement of the scope, you can
penetrate and damage the wall. Another clinical
example is with elderly individuals. In the
elderly, they have decreased salivary-gland
secretions and, if they’re taking numerous
pills and don’t drink enough water, a pill
can lodge at these points of constriction.
And if a pill remains lodged at a point of
constriction for too long of a period of time,
that can irritate the mucosa of the esophagus
and cause esophagitis.
This slide represents the fact that the esophagus,
like other tubular organs, can form diverticula.
There are three main diverticular sites. The
first one is at this level. This is occurring
at the junction between the pharynx and the
esophagus itself. And you can see the fact
that there is a diverticulum or an outpouching
of mucosa and submucosa at this superior point.
This is referred to as a pharyngo-esophageal
diverticulum also known by the eponym Zenker’s
diverticulum. Another area of the esophagus
that can develop diverticula is the mid-esophagus.
And here you have a diverticulum within the
mid-esophagus. And then the third most frequent
site is a formation of a diverticulum just
above the level of the diaphragm. That will
be termed an epiphrenic diverticulum.
This slide of the esophagus is demonstrating
two triangles that are located at the level
of the proximal esophagus. Those two triangles
are Killian’s triangle and Laimer’s triangle.
And Killian’s triangle is represented in
this particular area. The apex of Killian’s
triangle is projecting superiorly. The base
is inferiorly directed. And then the Laimer’s
triangle is shown right below. So, its base
is superior and its apex is directed inferiorly.
The borders of Killian’s triangle will be
the cricopharyngeus muscle. And we have the
transverse muscle fibres of the cricopharyngeus
muscle. This is the inferiormost component
of the inferior pharyngeal constrictor. It
also represents the upper esophageal sphincter.
And then, this portion of the inferior constrictor,
where we have these oblique fibres, this represents
the thyropharyngeus part of your inferior
constrictor. And so, the area between those
oblique fibres in the transverse fibres represents
Killian’s triangle. This is a potential
site of weakness and when a Zenker’s diverticulum
or a pharyngo-esophageal diverticulum forms,
it is within Killian’s triangle.
Laimer’s triangle is going to be bordered
by the transverse fibres of the cricopharyngeus
at its base. And then this oblique orientation
here coming to a convergence at the apex represents
a structural defect within the muscularis
externa of the esophagus. This area just has
the circular fibres of that muscularis externa
and the longitudinal fibres are very poorly
developed here. This is another potential
site of weakness and less frequently it too
can provide for the formation of a diverticulum.
Here we have a normal endoscopic view of the
esophagus. Here, you can appreciate the whitish
nature of the mucosa. This is imparted by
the fact you have a thick epithelial stratified
squamous epithelium here, so it’s difficult
for the blood vessels to shine through.
Now, the next slide is another endoscopic
view, but this is a pathologic view of the
esophagus. Here the esophagus looks very,
very angry and you can see that there are
bulges underneath the mucosal components.
And these bulges represent dilated esophageal
varices. And esophageal varices can form when
you have hepatic portal hypertension. And
the causative factor for hepatic portal hypertension
is cirrhosis of the liver. In severe cases,
these esophageal varices can rupture and as
a result, the patient will vomit blood as
a result of that rupture.
That now brings us to the key take-home messages
from this presentation.
The lungs are contained in pleural cavities
limited by visceral pleura and parietal pleura.
A thoracentesis may be performed to remove
excess fluid from the pleural recesses.
The trachea begins at vertebral level C6 and
bifurcates into primary bronchi at T4/T5.
The wall of the trachea consists of the mucosa,
then moving outwards, submucosa, the cartilage
fibromuscular layer and then, the externalmost
layer’s your adventitia.
Primary, secondary and tertiary bronchi respectively
supply the entire lung, lobes and bronchopulmonary segments.
The esophagus is divided into three parts:
cervical, the thoracic part, which is its
longest part, and then a short abdominal part.
The esophagus is anatomically constricted
at three main points and
is subject to formation of diverticula.
The esophageal wall consists of four layers:
mucosa, submucosa, muscularis externa and
throughout most of its extent, an adventitia
except for the short abdominal segment which
is limited by a serosa.
Thank you for joining me on this lecture about
the pulmonary structures and the esophagus.