Video: Esophagus in situ

Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the esophagus and, this time, we’re going to be looking at it in situ. So what we are going to be doing is exploring this image that you see right now on the screen which is the anterior view of the open thorax. So, imagine that we open the thorax as you can see here and then remove the lungs, also the heart, and then left here, you can see a bit of the esophagus and also this structure here which is the trachea. You see a bit of the aortic arch, the thoracic aorta right here. Another important structure, the diaphragm and the stomach – just a few things so you can understand what’s happening here on this image.

Now, if I remove all these blood vessels, all the structures that you see here, you can then see highlighted in green the structure that we’re going to be talking about, the esophagus.

Now, on the first part of this tutorial, we’re going to be talking about the anatomy and functions of the esophagus, whereas, on the second part, we’re going to be focusing on the surrounding elements or the different neighboring structures that you find here around the esophagus.

As I mentioned, we’re going to be continuing on talking about the anatomy and functions of the esophagus. And in order to do so, I’m using this image right now which is an image of the lateral right view of the thorax if we were to cut your torso, as you can see here, this is the cut area and then expose, we just removed here then the right lung to then be left with the different structures that you see here including this highlight which is then the esophagus. You can see here the heart which is then enclosed by this structure which is the pericardium. You can also see here the superior vena cava, an important blood vessel, and the trachea. And this part here is then the chest – this is your chest and this is your back. So, as you can see here, the green highlight is the esophagus.

Now, the esophagus is none other than a fibromuscular tube through which then food will pass through and it does so through peristaltic contractions, so, movements of muscle that will allow food to go through from the pharynx all the way to your stomach. Now, in humans, the esophagus is a round 18-25 cm in length. Now, it also travels behind the trachea as you can clearly see here on this image, and the heart, and passing through the diaphragm and then empties into the cardia of the stomach.

As we move on, we’re going to now show you the highlighted esophagus here, now seen from an anterior view of the thorax. I’d like to add that the esophagus can be divided into 3 parts. Now, these 3 parts include a cervical part, a thoracic part, and also the abdominal part of the esophagus and we’re going to be highlighting them on the next slides.

Now, as I highlight the different structures, different parts of the esophagus, what I’m going to be doing is also mentioning the blood supply and innervation for each part of the esophagus.

Now, the one you see here highlighted which is found a bit closer to the neck then you call it the cervical part of the esophagus. Now, when it comes to the blood supply of the cervical part of the esophagus, the inferior thyroid artery and also the inferior thryoid vein are responsible for the blood supply of this part of the esophagus. I do here a zoom in using this image, you can see a bit of the cervical part of the esophagus here highlighted in green behind the structure which is the trachea.

The next part that we’re going to be highlighting here on the image, this is then the thoracic part of the esophagus. When it comes to the blood supply of this part of the esophagus, the bronchial arteries and branches directly from the thoracic aorta will be supplying this part of the esophagus and, in terms of venous supply, the azygos and hemiazygos veins are going to be then draining this area of the esophagus. And, on this image, you can see a bit more structures here. I just added the layer where you can still see the highlighted thoracic part of the esophagus. So, in other words, the thoracic part of the esophagus is a portion that you find within the thorax because if you go a bit further down, you’re going to find this portion that you see here, this part highlighted in green, which is then the abdominal part of the esophagus which is the portion of the esophagus that is then connecting to the stomach.

Now, a quick word on the blood supply of the abdominal part of the esophagus. The left gastric artery and also the phrenic artery are responsible for supplying this area of this part of the esophagus with oxygenated blood. Now, the left gastric vein is then responsible for draining the abdominal part of the esophagus. You can also see here on this image other structures added so you can have an idea of how the abdominal part of the esophagus relates to the other structures that you find. Anyway, we’re looking at the esophagus in situ meaning that we’re looking at it with other structures that surrounds it.

We’re moving on and looking at then now the innervation of the esophagus. Now, the esophagus is innervated by the structures that you see here highlighted in green. These nerves which are known as the left and right vagus nerves. The esophagus is also innervated by the cervical and thoracic sympathetic trunks.A quick note on the innervation: The vagus nerve and the sympathetic trunk innervate the smooth muscle directly (found in the middle and lower parts of the esophagus). Whereas the striated muscles of the upper part are supplied by the recurrent laryngeal nerves (of the vagus nerve).

Now, I would like to add a quick word on the function or the role associated to the esophagus. We have mentioned a couple of functions throughout this tutorial but some of the important ones is to also transport saliva, liquids and food from the mouth all the way to your stomach.

As I mentioned before, the second part of this tutorial will be dedicated to talking about the different and neighboring or surrounding structures that we find then around the or nearby the esophagus. Now, some of them include different arteries that we’re going to be seeing here, the structures that you see here in red on this image on the right side. Before we talk about them, I’d just like to add a list here. We’re going to be seeing the aortic arch, the thoracic aorta, the brachiocephalic trunk, the right and left common carotid arteries, and the subclavian arteries.

We’re moving on and start talking about these structures that I just listed and the first one that you see here highlighted in green is known as the aortic arch. Now, the arch of the aorta also known as the transverse aortic arch is the part of the aorta that begins at the level of the upper border of the second sternocostal articulation of the right side. Now, as you can see here on this image, the aortic arch is going to run upwards and then backwards and to the left in front of the trachea as you can see here. It is then directed backward on the left side of the trachea and finally passes downward as you can see also here on the left side of the body of the 4th thoracic vertebra. Now, right about here, it becomes then continuous with this structure here which is then known, start calling it, the descending aorta which then the descending aorta becomes the thoracic aorta and further down it then becomes the abdominal aorta. Now, if I add here a few more structures, you can see how the nerves are related and we’re going to talk about the structures on or later on on this tutorial.

But now we’re going to move on to another portion of the aorta known as the thoracic aorta but you can also call it the semi-aorta because as I mentioned before, the descending aorta can be split into 2; the thoracic aorta which is the portion of the descending aorta that you find on the thorax as you can clearly see here highlighted in green and as it crosses the diaphragm then it becomes the abdominal aorta. So as I mentioned before, this portion begins at the aortic arch and runs down through the chest and abdomen.

Moving onto another structure that we saw on that previous list of arteries, we’re looking now highlighted in green at the brachiocephalic trunk. Now, this can also be called the brachiocephalic artery or innominate artery and this is an artery of the mediastinum that supplies blood to the right arm and the head and neck. Now, as you can see here on this image, this brachiocephalic trunk is the first branch coming from the aortic arch and that it will divide into 2 important arteries. One is the right common carotid artery which you see here and the other one is the right subclavian artery which you also see here on this image.

Knowing that, we’re going to move on and talk about these 2 arteries that you see here highlighted in green on the image, and on the left side, you’re looking at the left common carotid artery while on the image on the right side, you see here the right common carotid artery. Now, these are the largest and most important arteries of the neck. The left one as you can clearly see here on this image branches directly out of this structure here, the aortic arch. So, the aortic arch is going to serve as an origin point, let’s say, for the left common carotid artery. Now, the right common carotid artery – if you remember from the previous slide – it is branching off then this structure here that we just looked at before the brachiocephalic trunk. Now, as these arteries go up, they’re going to then split into 2 important branches, the internal and external carotid arteries.

We’re going to continue on to these structure that you see here highlighted in green. We’re looking at the subclavian arteries. Now, these are paired major arteries that you find on the upper thorax below, just below the clavicle. As you can clearly see here on this image, the left subclavian artery originates from the aortic arch that branches off of the aortic arch while the right subclavian artery originates or branches off the brachiocephalic trunk, the structure that we talked about before. Now, the left subclavian artery supplies blood to, as you would expect, the left arm, and then the right one will be then supplying blood to the right arm with some branches then supplying the head and thorax.

Now that we covered the different arteries, we’re going to move on to other surrounding or neighboring structures but this time, we’re going to be talking about the different veins that you see here on this image. And the list includes the left and right internal jugular veins, the subclavian veins, the left and right brachiocephalic veins, and the superior vena cava.

We’re going to start off with this that you see here highlighted in green. These are the internal jugular veins. On the left side, you’re looking at the right internal jugular vein while on this image on the right side, we’re looking at the left internal jugular vein. Now, these veins bring deoxygenated blood from your head back to your heart via the superior vena cava which you can see a little bit here on this image.

Before we’ll move on and talk about different structures, I’d just want to give you an overview of how blood goes from the right and left internal jugular veins back to your heart. Now, we also have to remember that blood will be coming from the left and right external jugular veins and then from these veins that you see here highlighted on these 2 images, the left and right internal jugular veins, and all these veins will be then draining into the subclavian veins. And you can see here then the subclavian veins on these images. Now, the blood will go then into the brachiocephalic veins which you can also see here on this images, as you can see, as I’m pointing out, and then the blood will go into the superior vena cava which you see here a bit of the superior vena cava, and into the right atrium of your heart.

Now that we just talked about the trajectory of the blood from the left and right internal jugular veins, it is time for us to move on to another set of highlights here, and these structures that you see highlighted in green are the subclavian veins. Now, they are a paired large veins, one found on each side of your body as you can see here. Their diameter is approximately the size of your smallest finger, and they will be receiving blood from the axillary and jugular veins. And then, they will be draining into these structures here which are then known as brachiocephalic veins which happened to be the next veins that we’re going to be seeing here highlighted in green. And on the image on the left side, you see the right brachiocephalic vein while on the image on the right side, you see the left brachiocephalic vein.

Now, these veins are found on your upper chest and they’re formed by the union of each corresponding internal jugular vein and also the subclavian vein. So, if I take this one as an example, you can see here the internal jugular vein uniting here with the right subclavian to then form the right brachiocephalic vein. Now, one quick note that the left brachiocephalic vein is usually longer than the right one. Now, these vessels will then merge to form another very important vessel, the superior vena cava, which you can find here on these 2 images just behind the junction of the first costal cartilage with the manubrium of the sternum. Now, the brachiocephalic veins are the major veins returning blood to the superior vena cava.

And speaking of which we’re going to talk about now this structure that you see here highlighted in green, the superior vena cava, which is relatively large in diameter yet short. This vein will be carrying then deoxygenated blood from the upper half of your body all the way to the right atrium of your heart. And as I mentioned on previous slides, this vein will be receiving blood from the brachiocephalic and another vein, the azygos vein.

Now that we talked about the different veins that we find as neighboring structures of the esophagus, we’re going to start covering the different nerves. And the list includes the left and right recurrent laryngeal nerves and the anterior vagal trunk.

Starting off with the very first ones on the list that you see here highlighted in green on the image on the left side, you’re seeing then the left recurrent laryngeal nerve while on the image on the right side, we’re looking at the right recurrent laryngeal nerve. Now, these nerves are branches of the vagus nerve and they emerged from the vagus nerve at the level of the arch of the aorta and then travel up side to the side of the trachea and also the larynx. Now, as you can clearly see her on these images, they are not symmetrical so these nerves are not symmetrical. While the left recurrent nerve – as you can see here – will be looping around the aortic arch. The right recurrent laryngeal nerve will be looping around the subclavian artery. Now, the recurrent laryngeal nerves will be controlling all intrinsic muscles of the larynx except for the cricothyroid muscle. Now, these muscles act to open and close your vocal cords and also include the posterior cricoarytenoid muscle, the only muscle to open the vocal cords. Now, these nerves also carry sensory information from the mucus membranes of your larynx just below the lower surface of the vocal folds as well as carrying sensory secretory and motor fibers to the cervical segments of the esophagus and the trachea.

Next structure that we’re going to be highlighting here on this image of the anterior view is known as the anterior vagal trunk. Now, this structure is a branch of the left vagus nerve which you can also see here, this is the left vagus nerve and see how the anterior vagal trunk is a branch of the left vagus nerve. The anterior vagal trunk will be contributing what you also see here, this mesh of nerves which is known as the esophageal plexus. Important to note that the anterior vagal trunk will be giving off several branches including the hepatic branch which supplies then the liver, a celiac branch which are smaller branches which provides parasympathetic innervation to the celiac plexus, and also an anterior gastric branch or branches which then will supply your stomach. There is also a posterior vagal trunk which you cannot see here on this image and it is very similar to the anterior one. The posterior vagal trunk is also a branch of the vagus nerve which contributes to then the esophageal plexus.

Now, that we covered all the nerves, all the arteries and veins, we’re going to continue on in exploring some of the structures that you see here on this image that are found nearby the esophagus. Now, the first one that I’m going to be highlighting here one that I talked about before, this is the trachea. Now, this is basically a tube and is connecting the pharynx and larynx to then the lungs allowing then air to pass through. Now, the human trachea has a diameter of about 25 mm and the length of about 10-16 cm. And as you can clearly see here on this image, the esophagus just lies posteriorly to the trachea.

As we go down on the trachea, you can find here this split which we call then the tracheal bifurcation and this is a division of the trachea into the right and left main bronchi. Now, this split, this tracheal bifurcation happens at the level of the 5th or 6th thoracic vertebral body. Now, as for the results of this split, you see here these 2 bronchi. On the image on the right side, on the left side, this is the right main bronchus and on the image on the right side then you see the left main bronchus. Now, a bronchus which is singular for bronchi is also known as the primary bronchus or main bronchus. This is a passage in your respiratory tract that conducts air into your lungs. Now, the bronchus will be then branching into smaller tubes which in turn become bronchioles. And one important note to make here that there is no gas exchange taking place on your bronchi. And as I mentioned before, the trachea will be dividing into 2 main primary bronchi, the left and right ones, which you see here on the images and these happens then at the level of the sternal angle of the 5th or 6th thoracic vertebrae.

Now, let’s take a closer look here at the structure which is then the right main bronchus. The right main bronchus is wider, shorter, and more vertical than the left main bronchus. As one will be entering the right lung at approximately the 5th thoracic vertebra, the right main bronchus divides into 3 secondary bronchi also known as lobar bronchi which then deliver air to the three lobes of the right lung – the superior, middle and inferior lobes.

The next one that we’re going to be seeing here, this highlight, this is then as you remember the left main bronchus. This one is smaller in caliber but longer than the right being about 5 cm long, will be entering the root of the left lung opposite to the 6th thoracic vertebra. The left main bronchus divides into the two secondary or lobar bronchi to then deliver air to the two lobes of the left lung – if you remember – the superior and inferior lobes. Just for a bit of location, we’re going to show you this image here. This is the highlight of the first rib. The first rib is the most curved and usually the shortest of all ribs and you can see here as a point of location on this image.

The next important structure that we’re going to be covering here is the pleura. Now, these structures that you see here where we just removed the lungs and we see these empty spaces. Now, this sac-looking structures are known as the pleura and they can be divided into other structures. Now, this is serous membrane which folds back onto itself to form a 2-layered membrane structure. Now, the thin space between the 2 pleural layers is known as the pleural cavity and normally contains a small amount of pleural fluid. Now, the outer pleura or the parietal pleura is attached to the chest wall as you can see here on this image which we will then talk about. Now, the inner pleura which we also call the visceral pleura covers the lungs and joining structures via blood vessels, bronchi, and nerves.

Now, we’re going to start here by talking about then the parietal pleura which lines the thoracic wall, covers the superior surface of the diaphragm as you see here on this image, and also separates the pleural cavity from the mediastinum.

Now, we’re going to be seeing different portions or parts of the parietal pleura that have received special names that we’re going to be talking about on the next images and now we’re highlighting one of them which is known as the cervical part of the parietal pleura also known as pleural cupula and this structure rises into the neck over the apex of the lung. The other part of the parietal pleura that we can highlight here is known as the costal part of the parietal pleura and the costal pleura is a portion that lines the inner surfaces of the ribs as you can clearly see here, and also the intercostal muscles. A bit further down, we’re going to be highlighting this portion of the parietal pleura that lies on top of the diaphragm and for that reason we’re going to be calling it the diaphragmatic part of the parietal pleura. Now, as you can see it clearly lines the convex surface of the diaphragm.

Finally, we’re going to be highlighting this part of the parietal pleura which is known as the mediastinal part of the parietal pleura which is then lining other thoracic viscera. You can also see this image of the mediastinal part of the parietal pleura with a bit more structures for so you can understand how this structure is lined up along other structures.

Now, we’re moving on. I’m talking about these folds that you find here a bit further down which are known as the costodiaphragmatic recesses. They’re also known as the phrenicocostal sinuses. Now, this is a potential space in the pleural cavity at the posterior most tips of the cavity located at the junction of the costal pleura and the diaphragmatic pleura. It measures about 5 cm vertically and it extends from the 8th to 10th ribs along the mid-axillary line.

We’re moving on, continue here with the costodiaphragmatic recess but to show you here an image with the lungs so we can talk about the role of the costodiaphragmatic recess. Now, the lungs expand into this recess during forced inspiration. However, the recess never fills completely. During expiration, when you breathe out, it will then contain no lung tissue, only pleural fluid.

Next on our list we’re going to be highlighting another recess. This time it’s known as the phrenicomediastinal recess which is the recess found at the juncture between the diaphragmatic and mediastinal pleura coursing along the line of the attachment of the pericardium to the diaphragm.

Another structure that you’ll find here is known as the pericardium. Pericardium, if you remember, is a double-walled sac containing then and envelops your heart and the root of the great vessels. We’re going to be talking about it on a separate tutorial on more detail. But just a quick note here that the pericardial sac has 2 layers, a serous layer and a fibrous layer – just a reminder – and it also encloses the pericardial cavity which contains then pericardial fluid. The pericardium also has important roles. One of them is that it fixes or secures your heart onto the mediastinum, it also protects it against infections, and provides lubrication for the heart.

Next, I’m going to show you here an image of the highlight of the pericardium where you see it covering some of the main vessels. Notice here, you see the thymus here and just behind it, you’ll find or enclosed or envelop by it, you see the heart.

Next, we’re going to be talking about this muscle here, a very important muscle known as the diaphragm. This is a sheet of internal skeletal muscle that extends across the bottom of the ribcage and has also a very important role. One of them is in terms of structure, it separates the thoracic cavity containing your heart and lungs from the abdominal cavity. So as you can see here, you have your thoracic cavity here. Just under it, you’ll find then the abdominal cavity. And a very, very important role associated to the diaphragm is that it plays an important role in respiration. So, as you diaphragm contracts, the volume of your thoracic cavity increases and then air is drawn into your lungs.

Finally, I just want to highlight this structure here so we know what’s happening on this image. And I talked about this one before. This is the stomach, which is as you probably know, a very famous organ which is a muscular hollow dilated part of the digestive system which functions as an important organ of the digestive tract in general. It is as you probably remember we will talk about in more detail on separate tutorials, this organ is involved in the second phase of digestion following then mastication or chewing. And the stomach is located between two important structures. One of them which is the main topic of this tutorial, the esophagus, and the other one is the small intestine.