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Pulmonary structures and esophagus

by Craig Canby, PhD
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    00:01 Welcome to this lecture on Pulmonary Structures and Esophagus.

    00:06 This slide captures the learning objectives that you should be able to answer at the conclusion of this lecture.

    00:13 First, describe the pleural membranes and associated recesses.

    00:18 Describe the trachea, its wall composition and bronchial branching pattern.

    00:26 Compare and contrast the features of the right and left lungs.

    00:30 Describe the applied anatomy in performing a thoracentesis.

    00:34 Describe the esophageal segments, constrictions and the layers forming its wall.

    00:41 Describe the locations of esophageal diverticula and the relevance of Killian’s triangle.

    00:49 And then we’ll summarize the key take-home messages from this lecture.

    00:53 Lastly, we’ll provide attribution for the images that were used throughout this presentation.

    01:02 Here is our body map and most of our attention is going to be focused in the pleural cavities.

    01:11 And then, we’ll also focus some of our attention in the mediastinum when we look at the esophagus and trachea, bronchi.

    01:23 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.

    01:40 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.

    01:57 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.

    02:16 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.

    02:43 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.

    03:00 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.

    03:53 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.

    04:20 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 anatomic relationships.

    04:40 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.

    04:56 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.

    05:13 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.

    05:37 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.

    05:51 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.

    06:04 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.

    06:39 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.

    06:55 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.

    07:20 We have the same costodiaphragmatic recess that’s situated here on the left side as well.

    07:29 The costomediastinal recess is along in through here with the right lung.

    07:36 We also have one on the left side.

    07:39 This represents the point where the costoparietal pleura is going to bend and become the mediastinal parietal pleura.

    07:49 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.

    08:22 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.

    08:46 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.

    09:02 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.

    09:20 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.

    10:00 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.

    10:11 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.

    10:58 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.

    11:21 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.

    11:35 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.

    11:48 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.

    12:08 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.

    12:46 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.

    13:12 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.

    13:31 The submucosa is going to be characterized by the presence of numerous glands that we see here.

    13:39 The cartilaginous fibromuscular layer is demonstrated here where we have the hyaline cartilage.

    13:46 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.

    14:12 The outermost layer is your adventitia. That is simply a connective-tissue coat.

    14:20 There are various types of bronchi. So, let’s describe the various divisions of the bronchi.

    14:28 The first bronchi that form will be those bronchi that divide where the trachea ends.

    14:35 And these are primary bronchi: a right one and a left one.

    14:40 So, we have one primary bronchus for each lung.

    14:44 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.

    15:30 Each secondary bronchus will then divide into tertiary segments. And we see numerous tertiary segments in each one of these branching patterns.

    15:42 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.

    16:10 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.

    16:34 Here’s your right lung. It has two fissures. One here: this is called the transverse fissure.

    16:44 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.

    17:08 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.

    17:34 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 lingula.

    18:02 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.

    18:59 So, it has relationships to the rib cage.

    19:03 The mediastinal surface is this area here and this is the surface of the lung that will face the mediastinum.

    19:12 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.

    19:27 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.

    20:00 Here we’re looking at the left lung. It only has one fissure: the oblique fissure.

    20:06 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.

    20:19 And again, we can see the cardiac notch.

    20:22 And you can see the lingula associated with that superior lobe.

    20:29 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.

    21:01 And so, if we take a look here, we have the right lung above, its hilum is shown here.

    21:08 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.

    21:31 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.

    21:46 In the left lung, its hilum will also have a pulmonary ligament.

    21:52 Now, within the hilum, we’ll have a relationship of the airways to the vascular structures.

    21:57 It’s going to be a bit different between the right lung and the left lung.

    22:05 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.

    22:36 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.

    22:55 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 airway.

    23:27 The following slide will introduce you to the concept of bronchopulmonary segments.

    23:33 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.

    23:59 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.

    24:14 The slide that you now see shows the various bronchopulmonary segments in the right lung.

    24:22 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.

    24:36 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.

    25:01 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.

    25:58 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.

    26:36 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.

    26:52 Each pulmonary acinus is going to be fed by a type of bronchiole called the terminal bronchiole.

    27:00 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.

    27:38 Venous blood is going to be drained at the periphery of this organizational unit, the acinus.

    27:52 Now, let’s shift our focus to the esophagus.

    27:56 And the first aspect about the esophagus is the fact that it’s divided into three parts.

    28:04 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.

    28:42 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.

    29:08 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.

    30:12 This slide depicts various constrictions that can be seen along the length of the esophagus.

    30:20 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.

    30:49 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.

    31:43 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.

    32:35 This slide represents the fact that the esophagus, like other tubular organs, can form diverticula.

    32:44 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.

    33:04 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.

    33:20 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.

    33:40 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.

    33:55 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.

    34:20 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.

    34:42 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.

    35:12 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.

    35:56 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.

    36:18 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.

    37:15 That now brings us to the key take-home messages from this presentation.

    37:21 The lungs are contained in pleural cavities limited by visceral pleura and parietal pleura.

    37:27 A thoracentesis may be performed to remove excess fluid from the pleural recesses.

    37:35 The trachea begins at vertebral level C6 and bifurcates into primary bronchi at T4/T5.

    37:44 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.

    37:58 Primary, secondary and tertiary bronchi respectively supply the entire lung, lobes and bronchopulmonary segments.

    38:10 The esophagus is divided into three parts: cervical, the thoracic part, which is its longest part, and then a short abdominal part.

    38:21 The esophagus is anatomically constricted at three main points and is subject to formation of diverticula.

    38:30 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.

    38:49 Thank you for joining me on this lecture about the pulmonary structures and the esophagus.


    About the Lecture

    The lecture Pulmonary structures and esophagus by Craig Canby, PhD is from the course Thoracic Viscera. It contains the following chapters:

    • Pleural membranes
    • Trachea
    • The lungs
    • The esophagus

    Included Quiz Questions

    1. Mediastinal pleura
    2. Cervical pleura
    3. Costovertebral pleura
    4. Diaphragmatic pleura
    1. Costodiaphragmatic recess
    2. Vertebromediastinal recess
    3. Costomediastinal recess
    1. Tertiary
    2. Secondary
    3. Primary
    1. Superior lobe of left lung
    2. Inferior lobe of left lung
    3. Superior lobe of right lung
    4. Inferior lobe of right lung
    5. Middle lobe of right lung
    1. Aorta and left bronchus
    2. Junction of pharynx and esophagus
    3. Diaphragm
    1. Junction of pharynx and esophagus
    2. Mid-esophagus
    3. Immediately superior to the diaphragm
    4. Through the esophageal hiatus of the diaphragm
    5. Immediately inferior to the diaphragm

    Author of lecture Pulmonary structures and esophagus

     Craig Canby, PhD

    Craig Canby, PhD


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