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Lungs in situ seen from the anterior view.
Lungs In Situ - Human Anatomy | Kenhub
Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the lungs in situ. So, what we’re going to be doing basically is exploring the image that you see now on the screen which clearly shows here the 2 lungs – the right one and the left one – and then as you can see, we’re looking at them from an anterior view of the open thorax to understand a bit of what is happening here on this image. You notice here the heart, which is covered then by the pericardium, the thymus. You notice here the superior vena cava and this important muscle here, the diaphragm. And a lot of other structures that are connected, directly connected to the lungs or there found nearby these 2 organs.
So, a quick overview of what we’re going to be talking on this tutorial, we’re going to be discussing the anatomy and also the functions of the lungs, and then we’re going to be talking about those structures, those surrounding structures that you find near the lungs. Hence, the title of this tutorial, lungs in situ. You know these structures very well from probably elementary school, you started talking or heard about the lungs. Now, they are a pair of spongy air-filled organs that are located on either side of your chest. They are located within the thoracic cavity on either side of your heart and close to also your backbone.
Now, the lungs are enclosed and protected by the strong, strong structure known as the ribcage. And as you can also see here on this image that the lungs have broad bases which enable them to then sit upon this structure which is the diaphragm, and having these broad bases enable these organs to just sit on the diaphragm and prevent them from just being displaced.
Now, the lungs have 3 surfaces that we’re going to list here on this tutorial. One of them is closely related to the ribs, hence, the name costal surface. Now, this is the outer and in contact also with the costal pleura which we will be talking about but you see a little bit of the costal pleura here on this image. The other surface is known as the mediastinal surface which is the parts of the lungs that are in contact with this structure here that you’ll also see here which is known as the mediastinal pleura which then spacing the mediastinum. The other surface is known as the diaphragmatic surface which is then the surface that is in contact with this muscle that we talked about before, the diaphragm. Now, it is concave as you see also here and the diaphragmatic surface of the lungs is also forming an important part of these organs which is known as the base of the lungs which then rest on the diaphragm.
Now, the lateral and posterior parts of the lungs, they’re very thin and sharp margins and they will be projecting into these pockets, now, we’d say here, these recesses, which are well known as the costodiaphragmatic recesses and you can see 2 here on this image.
We’re going to start in highlighting a few structures here. The first one that you see on both lungs, this is known as the apex of the lungs or the pulmonary apex, which is the round upper part of the lung and it extends into the roof of your neck reaching between 2.5 to 4 cm above the level of the sternal end of the first rib, and you can see a little bit here of the first rib on both sides – so, these are the 2 first ribs.
Now, there is a sulcus which is produced by these 2 arteries here – the subclavian arteries – as it curves in front of the pleura. It runs upward and laterally immediately below the apex. It is positioned above the lobes and is partially responsible for filtering air.
Now, I would like to take a closer look at both lungs and we’re going to start talking about the right lung which is this one – so we’re looking at the subject’s perspective – and this is the right lung. Now, the right lung has a higher volume, total capacity, and weight than your left lung. And although it is 5 cm shorter due to the diaphragm which will be then rising higher on the right side to then accommodate an important organ as well – the liver – it is then broader than the left lung due to the cardiac notch that you see on the left lung.
Now, as I move on and show you here these images of the 2 lungs. On the left side, you see an image of the medial view of the left lung while you see also here the medial view but this time highlighted in green of the right lung. To show you here that the right lung is divided into 3 lobes. You’ll find here the superior, the middle, and also the inferior lobe. And these are divided by 2 fissures. You see one here, which is known as the oblique fissure which you also find an oblique fissure here on the left lung, and then there is this fissure which is unique to the right lung which is known as the horizontal fissure and you can clearly see then from a medial view of these organs.
Once again, we’re going to be focusing on this view here, where we see the lungs in situ to highlight this portion of the lungs which I just mentioned or talked about on the previous slide. This one is the superior lobe of the right lung. Now, the right upper lobe is one of the 3 lobes as we’ve seen before. It consists of 3 segments: an apical, the posterior, and also an anterior one.
A bit further down, we’re going to be highlighting another lobe of the lung, this one is known as the middle lobe of the right lung. And as a reminder, the middle lobe of the right lung has lateral and medial segments, and even further down we’re going to be highlighting here on this image now, the inferior lobe of the right lung. As you’ve seen also on previous slides, the oblique fissure will be separating the lower lobe from the middle and upper lobes. It is the largest of the 3 lobes of the right lung and is located behind and below the oblique fissure.
We’re going to move on and now talk about the other lung, the left lung, which you also see here clearly on this image, on the right side of the image but on the left side of the subject – so, this is the left lung. Now, the left lung is slightly smaller than the right one because 2/3 of the heart is located on the left side of your body – as you can see here. So, the heart is projecting to the left side of your chest and occupying more space on the left side. For that reason, your lung – your left lung – has to be a bit smaller in order to fit then your heart.
Now, the left lung, in order to create that space, extra space, to fit in your heart, has an important structure known as the cardiac notch, which is basically an indentation in the lung that surrounds the apex of the heart, so the tip of the heart. As a reminder here, the left lung can be divided into 2 lobes – as you now see here highlighted on the medial views of the lungs. So, there are 2 lobes: a superior which you can find here – this is the superior lobe – and the inferior lobe which is then divided by this fissure here which is then the oblique fissure.
Going back to this image of the anterior view, we’re now highlighting the superior lobe of the left lung. Now, this lobe as I mentioned before separated from the inferior lobe by then the oblique fissure and it is subdivided into then 4 bronchopulmonary segments, two of which represent the lingula. And going down, we’re going to see here this highlight which is then the inferior lobe of the left lung, and the inferior lobe of the left lung is then divided from the superior lobe by the, again, the oblique fissure. Now, this lobe is what basically forms most of the base of the left lung and also a great portion of the costal surface of the left lung and most part of the posterior border as well. Now, the inferior lobe is the larger of the 2 lobes of the left lung.
Also here on these images, you can find the fissures as you see now highlighted in green. Now, on both lungs, we have the oblique fissures highlighted right now, and as you probably remember from previous slides, the oblique fissures are going to then be separating the inferior from the middle and superior lobes on the right lung, and on the left lung, they’re going to be – this one – the oblique fissure is going to be separating the superior and inferior lobes. Its direction is, however, more vertical than the horizontal one and it cuts the lower border about 7.5 cm behind its anterior extremity.
Now, if we take a look at the right lung, we see here this unique fissure to the right lung, this is then the horizontal fissure of the right lung. This one will be separating the superior from the middle lobe. It begins in the lower fissure near the posterior border of the lung and running horizontally forward, cuts then the anterior border on a level with the sternal end of the 4th costal cartilage. Now, on the mediastinal surface, it may be traced backward on the hilum. And the hilum of the lung is this structure that you see here also on this image. This structure then in a way where all these blood vessels are entering the lungs.
Another important structure that we’re going to be highlighting here, this is known as the trachea. Now, the trachea is basically a tube and will be connecting the pharynx and larynx to your lungs and then allows passage of air. The human trachea has an inner diameter of about 25 mm and a length of about 10-16 cm. And as you can clearly see here on this image, you see this little structure here – it’s not little but you just see a little portion here – which is the esophagus which lies posterior to then the trachea. So the trachea is in front of your esophagus, don’t forget that.
Another structure we’re going to be highlighting here on this image, now, a bit of a zoom-in here so I can show you the left main bronchus. The left main bronchus is smaller in caliber but longer than the right one being about 5 cm long, and as you can see here, it is entering the root of the left lung opposite to then the 6th thoracic vertebra. The left main bronchus divides into 2 secondary or lobar bronchi to then deliver air to the 2 lobes of the left lung, the superior and inferior lobes.
Next, we’re going to be talking about then the parietal pleura – a very important structure that is closely related to then the lungs – and to say that the parietal pleura lines your thoracic wall. It covers the superior surfaces of the diaphragm and also separates the pleural cavity from the mediastinum.
Now, there are different parts of the parietal pleura that have received specific names – we love to give names here – in anatomy. So, these names will be basically indicating their position within the thorax. The first one that I’m going to be highlighting here, this is known as then the cervical part of the parietal pleura. And this part is basically rising into the neck over the apex of the lung. Another part of the pleura that you can see here now highlighted in green – I just removed here the left lung so you can see clearly highlighted – the costal part of the parietal pleura. And as the name clearly indicates, this is the portion that lines the inner surface of the ribs and intercostal muscles.
The next part of the pleura that you see now highlighted in green – also with the left lung removed so you can clearly see here – the diaphragmatic part of the parietal pleura which, as also the name indicates, this is the portion of the pleura that will be lining the convex surface of the diaphragm. And, finally, the last part of the pleura that I also talked about before, this is known as the mediastinal part of the parietal pleura. This portion is then surrounding the mediastinum surrounding also the thoracic viscera.
Next here on the image, I would like to highlight these pockets, these recesses known as the costodiaphragmatic recesses that I talked about before. Now, they are also known as phrenicocostal sinuses, or sinus as singular, and this is a potential space in the pleural cavity at the posterior most tips of this cavity – as you can clearly see here on this image – just located at the junction of the costal pleura – so you a bit here of the costal pleura – and also the diaphragmatic pleura. They measure approximately 5 cm vertically and they extend from about the 8th to 10th ribs along the mid-axillary line.
Now, I wanted to dedicate some slides here for the costodiaphragmatic recesses because they do have a role. Now, the role of these recesses is that your lungs will be expanding into them during forced inspiration, however, the recess never fills completely. And during expiration, it contains no lung tissue, only pleural fluid.
Next, we’re going to be highlighting this muscle that we also covered on a previous or previous slides, this is the diaphragm. Now, the thoracic diaphragm or simply the diaphragm is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. It definitely has a very important role especially not only structurally because it is separating the thoracic as you can see here, the thoracic cavity, from the abdominal cavity, and it also has a very important role in respiration. So, as your diaphragm contracts, the volume of your thoracic cavity will be increasing and air is then drawn into your lungs.
We’re going to move on and start talking about the different arteries that we find here on this image and before we do so, we’d like to quickly list them. So, we’re going to be talking about the aortic arch, the pulmonary trunk, the right and left pulmonary arteries, and also the brachiocephalic trunk. And let’s start with the very first one here on the list that you see now highlighted in green, this one is then the aortic arch.
The arch of the aorta or the transverse aortic arch is the part of this blood vessel that begins at the level of the upper border of the 2nd sternocostal articulation on the right side. And as you see here, it runs at first upward and then backward and to the left in front of the – as you can see here – the trachea that we talked about. It is then directed backward on the left side of the trachea and finally passes downward on the left side of the body, and as you can see here on this image – I just removed the heart and the lungs – to then expose here the aortic arch and the thoracic or descending aorta.
Next structures we’re going to be highlighting here which you see on both these images, now, these are the pulmonary arteries. Now, on the left image, you see here this highlight of the right pulmonary artery while on the right image, you see the highlight of the left pulmonary artery. Both arteries – pulmonary arteries – will be carrying deoxygenated blood from the heart to the lungs and they are some of the exceptional arteries other than the umbilical arteries in the fetus that will be carrying deoxygenated blood. So, as you remember, all arteries or most of the arteries in your body are carrying oxygenated blood instead.
Now, a closer look here at the right pulmonary artery – a zoomed-in image – where you see the right pulmonary artery or right branch of the pulmonary artery which is longer and larger than the left one and runs horizontally to the right behind the ascending aorta as you can see here – so this is the ascending aorta – and also this important vein, the superior vena cava, and also in front of the – which you cannot see here on this image – but in front of the right bronchus to then the root of the right lung. And here at the root of the right lung, you can see these 2 branches because this artery is going to be then divided into, dividing, into 2 branches. The lower and larger of these goes then to the middle and lower lobes of the lung and the upper or the smaller one will be then distributed to the upper lobe.
Now, going to this image where I’m now highlighting then the left pulmonary artery or left branch of the pulmonary artery which is shorter and somewhat smaller than the right one. This one will be passing horizontally in front of the descending aorta and the left bronchus which we talked about – the structure that you see here behind the left pulmonary artery – to then the root of the left lung where it’s going to be dividing into 2 branches, one for each lobe of the lung.
The next structure that we’re going to be highlighting here is the ligament and this ligament is known as the arterial ligament or the ligamentum arteriosum. Now, this is a small ligament which is attached to the superior surface of – as you can see here – of the left pulmonary artery and then goes all the way to attach to the aorta. This is a remnant of the ductus arteriosus and is formed within 3 weeks of birth. Now, this ligament has a major role in trauma. Now, it fixes the aorta in place during decelerations recoil consequently and potentially resulting in ruptured aorta.
Next in line, we’re going to be talking about another artery known as the brachiocephalic trunk or also known as brachiocephalic artery or innominate artery. Now, this is an artery of the mediastinum that supplies blood to the right arm and head and neck. It is the first branch of the aortic arch which you can also see here – so this is the aortic arch – this is the first branch coming out of the aortic arch and soon after it emerges, the brachiocephalic artery will be dividing into the right common carotid artery which is this one going upwards and the right subclavian artery which you can also see here on the image.
Now, that we just covered the different arteries that we find here on this image of the lungs in situ, it is time for us to talk about then the veins. And the main veins that you see here on this image include then the right and left brachiocephalic veins, the superior vena cava, and the pulmonary veins. So, let’s start by highlighting the very first 2 here on the list, the brachiocephalic veins.
On this image, you find here highlighted in green, the right brachiocephalic vein and on this one then you find the left one. Now, the brachiocephalic veins are formed by merging of 2 veins – and you can see here – the internal jugular vein which then meets with the subclavian vein and then they formed the brachiocephalic vein. Then the 2 brachiocephalic veins connect here, merged to form a very important vein, the superior vena cava. The main task of these veins is to transport deoxygenated blood of the upper extremity and head region towards then the superior vena cava and then to your heart. And then this blood when it reaches the heart is going to be pumped into the lungs.
The next structure we’re going to be highlighting here – one that I talked about before – this is the superior vena cava, and the superior vena cava is large in diameter – no doubt about it – but relatively short. Now, this vein will be carrying deoxygenated blood from the upper half of your body to then the heart’s right atrium. The superior vena cava will be receiving blood from the brachiocephalic veins and also from the azygos vein.
Next set of veins I would like to highlight here on both sides, we’re seeing the pulmonary veins. So, you see the right pulmonary veins and the left pulmonary veins. The pulmonary veins will be transporting – and write down on your notes – oxygen-rich blood from the lungs towards then the left atrium of your heart so it can then be pumped back into your body. Now, the pulmonary veins are somewhat exceptional when compared to other veins – they do not have valves. The right pulmonary veins are divided into the superior and also the inferior right pulmonary veins, as you can see here – so the superior and inferior. We’re going to see this similar pattern also on the left pulmonary veins that are then split into the superior and also the inferior left pulmonary veins, and you can see a little bit here also on this image, the superior and a bit of the inferior left pulmonary vein.
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Now, good luck everyone, and I will see you next time.