Video: Lymphatics of the lungs

Hello everyone! My name is Joao and welcome to another anatomy tutorial here at Kenhub. Today, we're going to be talking about the lymphatics of the lungs. In today's tutorial, we're going to look at the lymph nodes of the lung and surrounding structures. Once we've learned about the lymphatics of the lung, we're going to take a look at the clinical relevance of the pulmonary lymph nodes and their pathological role in cancer cell metastasis. We will be using this helpful diagram throughout today's tutorial so let's briefly talk about what we're looking at.

This is an anterior view of the lungs and airways with the descending thoracic aorta here and the venous brachiocephalic trunks here. The lymph nodes of the lungs and surrounding structures are shown here in yellow. Now remember that as we go through, we'll highlight in green the specific area we're talking about. First thing we need to do is to actually answer a question, what is the lymphatic system? Let's take a quick overview.

The lymphatic system is a huge network of tissues and organs which defend your body against disease-causing agents. Well, that's the main definition of the system. We can think of it as a filtering system. It is primarily made up of lymph. Lymph is the fluid that circulates throughout the lymphatic system. It originates as interstitial fluid and contains a variety of substances such as leukocytes, plasma proteins, water, chyle, glucose and salts. Now, these enter the lymphatic system through little capillaries that run into the lymph vessels which happen to be the next point here – lymph vessels. They are part of the lymphatic system and they transport lymph throughout your body. They contain valves just like veins so that lymph can travel in only one direction – forwards. You can see some lymph vessels on the image here.

Now, the third element that we find in lymphatic system is what we know as the lymph nodes, and lymph nodes are bean-shaped organs seen here on this image. They are found throughout the lymph vessels and these contain large numbers of B-cells and T-cells. The lymph nodes are responsible for filtering lymph fluid and removing infectious agents. Now, let's focus on the very first item on our list – lymph. And to do so, we're going to be using this image here showing a section of a lymph node.

As we mentioned, lymph travels in one direction only. Lymph enters into lymph nodes via several afferent lymphatic vessels and they exit the lymph node via efferent lymphatic vessels – don't forget that. Now, these are wider and fewer in number than afferent lymphatic vessels. Getting back to the lungs, let's first look at the superficial drainage of the lung.

The superficial tissue or parenchyma of the lungs as well as the visceral pleura which we know is the innermost covering of the lung are drained by a vast plexus of tiny lymph vessels which drain lymph from these areas towards the hilum of the lung. We'll see what happens to this collected lymph in just a little bit. Before looking at the deep tissues of the lung, we first need to remember that the left and right lungs differ slightly in their structure whilst the right lung contains three lobes, the left lung contains only two. In addition, the pattern of lymphatic drainage is also slightly different between the left and right lungs. Now, let's take a look at how this works.

Starting with the right lung, all lobes of the right lung first drain into the intrapulmonary nodes then onto the bronchopulmonary nodes at the hilum. From here, they drain into the right inferior tracheobronchial nodes towards the right superior tracheobronchial nodes. Then onto the right paratracheal nodes into the right bronchomediastinal lymph trunk and from here, it is emptied into the bloodstream.

Now, we're going to talk about what happens on the left lung. The lymph of the upper lobe of the left lung drains into the intrapulmonary nodes continuing onto and into the bronchopulmonary nodes also known as the hilar nodes then into the left inferior and left superior tracheobronchial nodes towards the left paratracheal nodes before entering into the left bronchomediastinal trunk before then being emptied into the bloodstream. The lower lobe follows the same pattern as the upper lobe up until the left inferior tracheobronchial node then it drains mostly to the right superior tracheobronchial nodes where it joins the same route as the lymph from the right lung.

You might be feeling a little bit boggled by now but don't worry, we're going to break this whole system down step by step. You're going to be a master on the lymphatics of the lungs by the time we finish this.

Now let's talk about the lymph nodes. We're going to start with these lymph nodes that you now see highlighted in green which are the intrapulmonary nodes. The first thing we want to look at is where they are located. The intrapulmonary lymph nodes are located around the bifurcations of the branching lobar bronchi like you can see here on the image. These lymph nodes drain the interstitium of the parenchyma of the lung which to you and me means the fluid-filled space in between the cells of the lungs. From here, transport of lymph is mainly caused by the action of breathing which brings us onto the next set of nodes which are the bronchopulmonary nodes which are these structures seen now highlighted in green.

The bronchopulmonary nodes are located in the hilum of the lung as you can see here on the image. The afferent lymphatic vessels of these nodes carry lymph from the intrapulmonary nodes into the bronchopulmonary nodes where the lymph is filtered some more. In addition to that, remember the lymph drain from the superficial tissue and visceral pleura of the lungs. This is also received by the bronchopulmonary nodes. After leaving bronchopulmonary nodes, the lymph is then once again propelled forward onto the lymph nodes we are going to see which are these right here – the inferior tracheobronchial lymph nodes.

The tracheobronchial nodes can be divided into inferior and superior groups. The inferior tracheobronchial lymph nodes are several large lymph nodes in the mediastinum inferior to the tracheal bifurcation as we can see here. These nodes receive afferent lymph vessels from the bronchopulmonary nodes. Again, the lymph is filtered. It is once again propelled forwards towards these here – the superior tracheobronchial nodes – which are the lymph nodes we're going to briefly talk about now.

The superior tracheobronchial nodes are comprised of several large lymph nodes in the mediastinum superior and lateral to the tracheal bifurcation as you can see here on this image. These nodes receive afferent lymph vessels from the bronchopulmonary lymph nodes as well as inferior tracheobronchial lymph nodes. You might be asking what happens here. Well, you guessed it. The lymph is then filtered some more before the afferent lymph vessels carry the lymph onwards to drain it into these right here – the paratracheal lymph nodes – the next lymph nodes on our list. The lymph is almost at its destination.

In terms of location, the paratracheal lymph nodes run superiorly along either side of the trachea as we can see here. These nodes receive afferent lymph vessels from the superior tracheobronchial lymph nodes and once again, the lymph is filtered, filtered and filtered and the efferent lymph vessels send the lymph onwards to drain into the next ones that you see here – the bronchomediastinal lymph trunks – the structures seen now highlighted in green on the screen. Well, the lymph is almost, almost home.

In terms of location, the right and left bronchomediastinal lymph trunks lie medial to the superior portion of the azygos vein and anterior to the vertebral bodies of the spinal column. Looking first at the right bronchomediastinal trunk, it is located posterior to the right brachiocephalic vein and anterior to the anterior scalene muscle. The right bronchomediastinal trunk is a lymphatic vessel which forms from the confluence of efferent lymphatic vessels received from the tracheobronchial nodes as you can see here on this image. Most often, the right bronchomediastinal trunk empties all the collected lymph into the bloodstream around the anterior aspect of the junction of the right subclavian and right internal jugular veins. Sometimes, however, it may instead join the right internal jugular and subclavian lymph trunks forming then this one right here – the right lymphatic duct – this structure that we see now highlighted on the screen.

Just a quick note here that we've changed the diagram to better show the duct. We're now viewing the body from the anterior aspect. As I just mentioned, the right lymphatic duct is a variable structure which means it's not always present. When it's there, it is usually about one point twenty five centimeters long and it arises from the junction of the right bronchomediastinal, the right jugular and the right subclavian lymph trunks. Once the lymph has entered the right lymphatic duct, it is returned to the bloodstream at the confluence of the right internal jugular and right subclavian veins.

So that's the lymph from the right lung. Now, let's look at the lymph from the left lung.

On this side, lymph drains into the left bronchomediastinal lymph trunk which receives efferent vessels of the left tracheobronchial lymph nodes. In terms of location, the left bronchomediastinal lymph trunk is found posterior to the left brachiocephalic and left internal jugular veins and also anterior to the anterior scalene muscle. The left bronchomediastinal lymph trunk usually drains into the bloodstream at the confluence of the left internal jugular vein and left subclavian vein or occasionally directly into the left brachiocephalic vein where the lymph carried by the left bronchomediastinal trunk may first empty into another lymphatic vessel known as the thoracic duct which you see now highlighted in green on the image before being returned to the bloodstream.

And yes, we now covered all the lymphatics of the lungs. Now, it is time for us to go over a few clinical notes related to these structures. Knowledge of the lymphatics of the lung is very important in both the staging and treatment of lung cancer. As lung cancer spreads and metastasizes from its primary tumor, it often does so via the lymphatic system and usually proceeds in a sequential order just like what we've learned.

Hypothetically, the sentinel lymph node is the first lymph node or group of lymph nodes draining a cancer such as this circled here. It is also the first place where cancer cells are most likely to spread. Using a technique known as sentinel lymph node biopsy, doctors can examine as to whether cancerous cells from a primary tumor have spread or metastasize to other parts. This is done by using special dyes injected into a tumor. These nodes can be identified and tested to see if the cancer has spread. And if there is a tumor in the lungs, it may metastasize to surrounding lymph nodes interfering with the flow of lymphatic fluid through the node. It may even block the lymphatic ducts.

With other pathologies of the lung, the bronchopulmonary nodes – the ones that we see now highlighted – are those which most frequently become enlarged. On radiography of the chest, this may be indicated as a classical hilar lymphadenopathy which may be caused by inflammation, cancer or carcinoma or infection such as tuberculosis.

So what have we learned about the lymphatics of the lungs? Hopefully, you're feeling a lot less boggled now but let's recap before we finish this tutorial.

We learned that the lymph enters into the lymph nodes via several afferent lymph vessels and exits out of the lymph nodes via a smaller number of efferent lymph vessels. We then discovered that lymphatic drainage differs slightly between the left and right lungs – who knew? So in order of flow, all lobes of the right lung first drain into the intrapulmonary nodes which drain the bifurcations of the branching lobar bronchi as we saw on this image. The lymph then follows onto the bronchopulmonary nodes at the hilum which we saw here. Next, it's onto the right inferior tracheobronchial nodes inferior to the tracheal bifurcation as seen here, and after that, the lymph drains into the right superior tracheobronchial nodes which are superior and lateral to the tracheal bifurcation as you saw here on this diagram. At this point, the right lung is joined by the lymph from the lower lobe of the left lung.

Next up are the right paratracheal nodes which run superiorly along the trachea as you saw here and from here, the lymph flows onwards into the bronchomediastinal lymph trunk posterior to the right jugular vein and anterior to the anterior scalene muscle which we had a look at here. Then, finally, the lymph is emptied into the bloodstream at the junction of the right internal jugular veins sometimes via the right lymphatic duct which, you may remember, is the structure sometimes formed by the joining of the bronchomediastinal lymph trunk, jugular lymph trunk and subclavian lymph trunk seen here.

Now onto the left lung. As we learned earlier in this tutorial, the lymph from the upper lobe of the left lung follows the same drainage pattern as lymph from the right lung. The only difference here is that lymph leaves the left bronchomediastinal lymph trunk and empties into the bloodstream at the confluence of the left internal jugular and subclavian veins. The lower lobe of the left lung follows the same pattern as the upper lobe until the left inferior tracheobronchial node. Then, it drains mostly to the right superior tracheobronchial nodes where it joins the same route as the lymph from the right lung.

And that brings us to the end of this tutorial on the lymphatics of the lungs. Thanks for watching this Kenhub tutorial. I hope you enjoyed it and good luck with your studies. I think you've got this.