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.