Lymphatics of the heart

Hello everyone! It's Megan from Kenhub here, and in today's tutorial, we’re going to talk about the lymphatics of the heart. In this video, we'll be exploring the pathways in which lymph travels from the heart to the venous system. Before we begin, let me give you a quick overview of what we're going to talk about today. First, we'll look at these two components separately – the lymphatic system and the heart – then we'll put them together and discover where and how these two components interact by looking at the lymphatics of the heart which is, of course, the topic of this tutorial. Finally, we'll conclude this tutorial with some clinical notes relevant to the topic.

First, let's take a look at the anatomy of the lymphatic system.

The lymphatic system is composed of lymphoid organs and lymphoid vessels. Lymph nodes are secondary lymphoid organs which are widely distributed throughout the body. We can now see them highlighted in green in our image on the right and I've circled some of them for you in blue. They are bean-shaped structures and each have at least one afferent vessel and one efferent vessel connecting it to the rest of the system. Vessels that carry lymph to a lymph node are called afferent lymph vessels and nodes that carry lymph away from a lymph node are called efferent lymph vessels.

Efferent lymph vessels may carry lymph to a vein, into a lymphatic duct or even to another lymph node. This means one lymph vessel could be efferent from one lymph node and afferent to another. Eventually, all lymph ends up in the venous circulation. Now, we'll take a look at the heart and the parts of it that are relevant to our understanding all of its interaction with the lymphatic system.

In this image, we're looking at the anterior aspect of the heart in situ with the lungs retracted. The heart is a muscular pump responsible for circulating blood throughout the body. It contains four chambers through which the blood passes and is made up of four layers. The heart is located in the mediastinum between the lungs and anterior to the trachea.

We'll now go through the four chambers of the heart in the same way blood travels from entering the heart as deoxygenated blood to leaving the heart as oxygenated blood to supply the body. The first chamber blood enters is the right atrium. In this image, we're again looking at the anterior aspect of the heart and the right atrium is highlighted in green. The right atrium receives deoxygenated blood from the venous system and when the right atrium contracts, the blood moves into the second chamber, the right ventricle, which is the structure we can now see highlighted in green.

When the right ventricle contracts, the deoxygenated blood travels into the lungs where it gets rid of carbon dioxide and picks up oxygen becoming oxygenated blood. When it returns to the heart, it enters the third chamber, the left atrium. This image shows us the heart from a posterior view with the left atrium highlighted in green. The four blue structures entering the left atrium are the pulmonary veins by which the oxygenated blood travels from the lungs into the left atrium. When the left atrium contracts, the blood moves into the fourth and final chamber, the left ventricle, which we can see here highlighted in green. Finally, when the left ventricle contracts, oxygenated blood is pumped through the aorta and distributed throughout the body.

When looking at the external surface of the heart, there are some marks and grooves that help us determine the boundaries of each chamber. Between the atria and the ventricles is a groove or sulcus called the coronary sulcus. The coronary sulcus is also called the atrioventricular groove. This sulcus separates the atria from the ventricles and we can see it here between the right atrium and the right ventricle. The right coronary artery and the lymphatic vessel called the right coronary trunk both occupy the sulcus.

The other groove that we're interested in is the anterior interventricular sulcus. As you can likely guess from its name, this groove is on the anterior surface of the heart and runs between the right ventricle and the left ventricle. This groove is also occupied by coronary vessels namely the anterior interventricular artery and the great cardiac vein. Again, we'll see shortly that an important lymphatic vessel called the left coronary trunk lies here as well.

The final aspects of the heart we'll look at today are the layers of tissue that make up the heart itself and if we cut into the heart to view the left ventricle as we've done in our image on the right, we can see these layers quite nicely. There are four layers that make up the heart. From internal to external, they are the endocardium which lines the chambers of the heart, the myocardium which makes up the musculature of the heart, the epicardium which covers the external surfaces of the heart and the pericardium which is a double-walled sac that encloses the heart.

So now that we've identified the key structures in the heart and the lymphatic system, let's take a look at how they interact. It's time to dive into the lymphatics of the heart. We'll work our way from the inside out, internal to external. Firstly, we'll consider the plexuses that are between the layers of the heart, the internal part of the heart. There are three lymphatic plexuses found in the heart, namely, the subendocardial plexus which is found deep to the endocardium or between the endocardium and the myocardium, the myocardial plexus which is found within the myocardium, and the subepicardial plexus which is found deep to the epicardium or between the epicardium and the myocardium.

Now that we're familiar with these plexuses, let's look at their pathway. So, basically, the subendocardial and myocardial plexuses send their efferent vessels to the subepicardial plexus. After receiving those tributaries, the subepicardial plexus gives rise to the right and left coronary trunks. So, we can now look at the heart externally and divide the heart into two – the right and left sides. The right and left coronary trunks that arise from the subepicardial plexus follow two different routes to join up with the venous system, and now we'll look at each of these in turn.

The right coronary trunk seen here highlighted on this image of the anterior view of the heart receives tributaries that drain lymph from the right border of the heart, the diaphragmatic surface of the right ventricle and the right atrium. This trunk runs in the coronary sulcus between the right atrium and the right ventricle adjacent to the right coronary artery. The right coronary trunk then courses anterior to the ascending aorta and terminates as it drains into the lymph nodes we now see highlighted in green – the brachiocephalic lymph nodes.

In the next image, we can see a lateral view of the brachiocephalic lymph nodes from the left hand side. These nodes are named for their close proximity to both the brachiocephalic veins and the brachiocephalic trunk. I've highlighted the brachiocephalic veins in gray for you on this image. The efferent vessels of the brachiocephalic lymph nodes then run superiorly joined with some other efferent vessels but most importantly, drain into the thoracic duct, which joins the venous system at the left venous angle. We can see the thoracic duct highlighted in green on our image.

What's important to note here is that lymph from the right side of the heart drains into the left venous angle. You can see that I've used an arrow to illustrate the pathway of lymph from the right side of the heart into the left venous angle which is now contained within the circle on your screen.

Now let's take a look at the left coronary trunk. The left coronary trunk travels superiorly in the anterior interventricular groove while receiving afferent vessels from the right and left ventricles as well as tributaries from the diaphragmatic surface of the left ventricle. This vessel then travels between the pulmonary artery and the left atrium before draining into the structures that we now see highlighted in green which are the inferior tracheobronchial lymph nodes. These nodes are named after their location at the inferior aspect of where the trachea bifurcates into the bronchi at the carina.

The efferent vessels of the inferior tracheobronchial lymph nodes run superiorly joined with some other efferent vessels but most importantly drain into the right lymphatic duct which joins the venous system at the right venous angle. The fact to highlight here is that lymph from the left side of the heart drains into the right venous angle. You can see that I've used an arrow to illustrate the pathway of lymph from the left side of the heart into the right venous angle which I've circled for you on your screen.

So as we've discovered, there's a crossed drainage pattern that exists in the heart. The pathways crossover and join the venous system on the opposite side. Lymph from the left side of the heart drains into the right venous angle and lymph from the right side of the heart drains into the left venous angle.

Like any other organ, the heart has lymphatic fluid that needs to be drained from its interstitial space. There are some instances where this is unable to happen as efficiently as it should and we're going to talk about this in our clinical notes.

Myocardial infarction or a heart attack can damage cardiac lymphatic vessels. This can lead to myocardial edema as a result of lymph drainage, and myocardial edema decreases cardiac output.

So, now, you're officially an expert on the lymphatic drainage of the heart but before I leave you, let's have a quick review to summarize what we talked about today.

So, lymph is collected from the interstitial space of the heart via three plexuses namely the subendocardial plexus which is found deep to the endocardium, the myocardial plexus which is found within the myocardium, and the subepicardial plexus which is found deep to the epicardium. Now, remember that the subendocardial and myocardial plexuses drain into the subepicardial plexus. And after receiving those tributaries, the subepicardial plexus gives rise to the right and left coronary trunks.

The right coronary trunk which lies in the coronary sulcus drains the right side of the heart. Lymph in the right coronary trunk travels to the brachiocephalic lymph nodes then to the thoracic duct joining the venous system at the left venous angle. The left coronary trunk which lies in the anterior interventricular groove drains the left side of the heart. Lymph in the left coronary trunk travels to the inferior tracheobronchial lymph nodes then to the right lymphatic duct joining the venous system at the right venous angle.

So, if you're going to take anything away from this tutorial, remember that lymph from the right side of the heart drains into the left venous angle and lymph from the left side of the heart drains into the right venous angle.

That brings us to the end of our tutorial on the lymphatics of the heart. I hope you find it useful and thanks for watching!