Structures seen on the thoracic surface of the diaphragm.
Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the thoracic surface of the diaphragm. So, what we’re going to be doing here on this tutorial is covering the major and also minor openings found on the thoracic surface of the diaphragm. So, essentially we’re going to be looking at the image that you see now on the screen. Now, this image is a cut on your thorax and what we’re doing is then looking from cranial view to then look at the different structures here that we find around the diaphragm – this muscle here.
The very first thing we’re going to be doing also is just describing what is the diaphragm which you see here on this image highlighted in green – this is an image of the anterior view of the thorax. You can see a few thoracic organs namely the heart, the lungs and, here, the diaphragm. And, if you remember, the diaphragm is essentially a musculotendinous sheet made up of then skeletal muscle and a central tendinous part. It is found in the trunk of your body and separates the thoracic and abdominal cavities as you can clearly see here – so you have the thoracic cavity and below you find a bit of the abdominal cavity and dividing then this green structure, the diaphragm or highlighted in green.
Now, the superior border of the diaphragm is continuous with the xiphoid process anteriorly to the lower six costal cartilages laterally and the first to the third lumbar vertebrae posteriorly – so just a bit of the coordinates if you want to find the diaphragm in your body using these bony landmarks as coordinates.
Now, the next slide that we’re going to see here, the next image going back to the thoracic surface of the diaphragm here, we’re highlighting now what is known to be as the right central tendon of the diaphragm. The diaphragm in the center is comprised of a tendon called the central tendon of the diaphragm and the central tendon of the diaphragm is comprised of a strong aponeurosis – and here we see the right central tendon to be more specific. Now, the central tendon plays a role in respiration. Contraction of your diaphragm during respiration draws the central tendon inferiorly. This will then partially flatten the dome of the diaphragm which results in lowering of intrathoracic pressure and, therefore, enlargement of the thoracic cavity allowing then air to enter your lungs.
If there is a right central tendon, there should be the next one that we’re going to be highlighting here which is then the left central tendon of the diaphragm. Now, this one is, as the name indicates, located on the left side of the diaphragm, and both the left and right central tendons of the diaphragm are located inferior to the fibrous pericardium which you also see a little bit here on this image – this is a cut of the pericardium. We should also note here that the central tendon fuses with the pericardium through a ligament known as the pericardiacophrenic ligament.
I’d like to add a few words on the innervation of the diaphragm and, to do so, I’m using now this image of the lateral view of the thorax. We just cut here a few structures, removed a lung, specifically, the left lung to then expose here the diaphragm as you can see, and this structure here that we’re going to be talking about which is the innervation of the diaphragm but you also see here a bit of the heart covered in the pericardium, and a very important blood vessel here known as the aorta. So, just a few structures here to understand what we’re looking at right now. So, this is the front of your chest and this is the back – your back.
So, the innervation of the diaphragm comes from the phrenic nerve which is the structure that I just pointed out and is highlighted in green. And this one arises – this nerve – will be arising from the fibers of the third to the fifth cervical spinal nerves. Now, the phrenic nerve provides motor innervation to the muscular part of the diaphragm and sensory innervation to the central tendinous part of the diaphragm. The diaphragm is certainly a very important structure in your body because it plays an important role in breathing. So, when you’re breathing, the diaphragm contracts to then enlarge the thoracic cavity and then reduces, in this way, intrathoracic pressure. Now, during inspiration, the central tendon of the diaphragm is then drawn anteriorly and also inferiorly.
Next, we’re going to be talking about the different openings that we see here because, as you saw before, the diaphragm sits between the thoracic and the abdominal cavities so a lot of structures need to be passing through the diaphragm to reach then the abdomen or they come from the abdomen to go into the thorax. Now, these openings are also known as apertures. These apertures then allow the structures to pass between the cavities – the thoracic and abdominal cavities, to be specific. Now, for the purpose of this tutorial, we will first look at the major openings and the structures that pass through them as well as the minor openings and, after that, the structures that will pass through these openings.
So, let’s start by looking at the major openings of the diaphragm. And there are three major openings in the thoracic diaphragm namely the aortic hiatus, the esophageal hiatus, and the vena caval foramen. And as you probably have noticed, these major openings are named after the largest structures that run through them. We’re going to start off by looking at this hiatus here that you see known as the aortic hiatus listed on the list that we saw on the previous slide. And here you see the aortic hiatus highlighted in green with the structure that passes through it. And you also see this image now where we see the diaphragm now from the abdominal cavity. So, this is the abdominal surface of the diaphragm where you can also see here the aortic hiatus with the structure that passes through it. So, we’re looking at the aortic hiatus seen from two different aspects.
In green, you can see then the structure that passes through it, the aorta, passing through this opening that is located just anterior to the twelfth thoracic vertebra between the two pleura of the diaphragm. Other structures that pass through this hiatus from the thoracic cavity to the abdominal cavity are then the azygos vein and the thoracic duct.
If you remember from the previous list, we’re now looking at the esophageal hiatus highlighted in green. This one is located just anterior to the aortic hiatus as you see here. Notice that this is the anterior portion of this – so this is the front of the diaphragm and this is your back as you notice here then a thoracic vertebra and a little bit of the sternum here – so, this should be around your chest, just a bit of location here. The structures passing through this opening include then the esophagus which is the largest structure passing through this hiatus, hence, the name. In addition, the esophageal vessels which include the branches of the left gastric artery and vein as well as the anterior and posterior vagal trunks – they also pass through the esophageal hiatus.
Next, we’re going to be highlighting this structure that you see now from both views, the abdominal on the top – the abdominal surface of the diaphragm – and the thoracic surface on the bottom. Now, here we’re looking now at the vena caval foramen. Now, the vena caval foramen encircles then a very important vessel, the inferior vena cava, which passes through it as well as some branches of the right phrenic nerve. And as you can see here, you notice on this image, the vena cava actually – highlighted in green – passing through this foramen.
We have listed now the major openings of the diaphragm to now list the minor openings and the structures that pass through them. The list includes then the lesser aperture of the right crus, the lesser aperture of the left crus, the medial and lateral lumbocostal arches, and the foramen Morgagni.
We’re going to start with the very first two of the list and, to do so, we’re going to be showing here these two images showing you the splanchnic nerves passing through the diaphragm and they’re going to do so by passing through the lesser aperture of the right crus and the lesser aperture of the left crus.
On this image here, you can see the splanchnic nerves entering the abdominal cavity through the small openings here which are then the lesser apertures and, on this right image, you can see then the splanchnic nerves in the thoracic cavity and here you also see them passing through the diaphragm which is the structure right here – so they’re crossing the diaphragm going into the abdominal cavity, and we’re looking at them right now from an anterior view of the thorax on this image. So, remember that the lesser aperture of the right crus and the lesser aperture of the left crus will be then transmitting the greater and lesser splanchnic nerves.
The next openings that we’re going to briefly discuss here that are not visible – quite visible – from the thoracic surface of the diaphragm but we are going to briefly mention them and show you these structures here. One of them is highlighted in green – another one here – these are then the sympathetic trunks, and they pass through the lateral lumbocostal arch and also the medial lumbocostal arch. Now, the sympathetic trunks, they run behind the diaphragm under the lumbocostal arches and both the medial and lateral lumbocostal arches, they contain areolar tissue when present and they also separate the superior and posterior surfaces of the kidney from the pleura. We will skip the foramen of Morgagni because we cannot clearly see it from the thoracic surface of the diaphragm but we’re going to move on and talk about the different other structures that we can see from this view – important structures worth remembering.
First one seen now highlighted in green which shows then the diaphragmatic part of the parietal pleura. Now, the diaphragmatic part of the parietal pleura – as you can see here in the thoracic cavity – is the part of the parietal pleura that covers part of the convex surface of the diaphragm and, just as a reminder, the pleura is a two-layered membranous structure that covers your lungs. There is an external layer known as the parietal pleura and then an internal one which is known as the visceral pleura. We also see here from this image of the anterior view of the thorax the diaphragmatic part of the parietal pleura where we just removed the lungs and then show you how it lies over part of the diaphragm.
The next structure we’re going to be highlighting here – as you can this really thin line highlighted in green – this is known as the costal part of the parietal pleura. Now, as the name suggests, it covers the inner surface of the ribs as well as the intercostal muscles. You can also see here the costal part of the parietal pleura now from this image of the anterior view of the thorax.
Next, we’re going to be highlighting the, another part of the parietal pleural, this time the mediastinal part of the parietal pleura which covers the mediastinum and is continuous with the costal part and also the diaphragmatic pleura and you can see also here from this anterior view of the thorax now with the structures that we find on the mediastinum.
Another structure we can find here from this image is known as an intervertebral disc – just a bit of location to understand what is happening on this image so you have a better understanding when we describe the thoracic surface of the diaphragm. To be specific, we find the intervertebral disc found between T8 and T9 vertebrae. There are a few structures that can be seen in relation to this disc, namely, the descending aorta located anteriorly as you can see here, a few veins here – the azygos and hemiazygos veins – located anterolaterally on the left and right side respectively, and also here the – if you remember – the sympathetic trunks that are located posterolaterally to this disc.
So, I’m just going to highlight here then the two sympathetic trunks – the right sympathetic trunk and the left sympathetic trunk. So, you have a bit of understanding what is happening here – notice these highlights. As I mentioned before, these structures pass through just behind the diaphragm under the medial lumbocostal arches on the left and right sides.
We also see here this structure that I’m now highlighting that I mentioned also before, this is known as the pericardium. The pericardium is a fibroserous double-walled sac that encloses your heart. The pericardial fluid and the roots of the great vessels are also capsulated within the pericardium and it is located within the middle mediastinum. Here we see the fibrous pericardium which is a layer of dense connective tissue and it is connected to the central tendon of the diaphragm through the pericardiacophrenic ligament – don’t forget this. You can also see here from this image of the anterior view a bit of the pericardium.
Next, we’re going to be highlighting here this structure which is known as the left costomediastinal recess which refers to a potential space between the costal and mediastinal pleurae on the left side. Now, this space plays a role during respiration and allowing deep expansion of the lungs during inspiration. There’s also a right one that you see now highlighted in green which also, as a function, allows expansion of the lungs during inspiration. It is located between the costal and mediastinal pleurae but this time on the right side.
We can also see here on this image, this little bit here which is part of the anterior mediastinum. It is bordered laterally by the pleurae and anteriorly by this structure here, the sternum, which means that the pericardium forms its posterior border which you can also see here that the pericardium defines its posterior border. The anterior mediastinum contains remnants of the thymus and some lymph nodes but we can't really see here on this image. I just wanted to highlight to show you that we see here a little bit of the anterior mediastinum.
Finally, the last highlight and topic and structure that we’re going to be talking about on this tutorial – one that I mentioned just earlier – this is the sternum, just a cut of the sternum to be more specific. Now, as I mentioned before, this forms the anterior border of the anterior mediastinum, and here we see a cross-section of the sternum at the level of the diaphragm. This long bone helps protects your lungs and heart and major blood vessels as well as forming the anterior part of the rib cage. It also provides attachment to the transversus thoracis muscles.
Now that you just completed this video tutorial, then it’s time for you to continue your learning experience by testing and also applying your knowledge. There are three ways you can do so here at Kenhub. The first one is by clicking on our “start training” button, the second one is by browsing through our related articles library, and the third one is by checking out our atlas.
Now, good luck everyone, and I will see you next time.