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Introduction to lymph nodes

Overview of the anatomy and function of the lymph nodes.

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When studying the regional anatomy of the body, here's the typical pattern. We learn about the bones, the muscles, maybe some organs if there are any in our region of interest. After that, we might spend some time exploring the arteries and the veins of the region, after which we would also take note of the nerves there also, and it goes without saying, that we would never forget to learn about the lymphatics and lymph nodes present before finishing, right? Well, well, not so much.

The lymphatic system very often doesn't quite make the cut, does it? It’s just one of those areas we don't often get round to learning. It happens so easily. You're cramming for an exam. So much to learn, so little time. Who needs to learn about the lymphatic system anyway, right? Wrong. Don't worry. If this has happened to you, you're certainly not the only one.

For decades, the lymphatic system was not just neglected by the anatomy student, but also by scientists, doctors, and even anatomy teachers. We all know the cardiovascular system inside out. After all, it's been studied extensively for as long as Anatomy has been studied.

The lymphatic system, however, has often been considered less important and certainly secondary to the blood circulatory system. Why is this, you ask. Why is the lymphatic system the forgotten child of anatomy? Well, there's several reasons, but it's partly down to the makeup or the morphology of the lymphatic system which until recently has been quite elusive and difficult to characterize. In addition to that, there's just so much confusion in the literature, different textbooks and papers all saying different things, and calling structures by different names.

In addition to that, for a long time, the various roles and functions of the lymphatic system especially in pathology has been equally difficult to define. Fortunately, times are changing. Advances in technologies such as medical imaging and renewed interest in the system is slowly bringing lymphatics back to its rightful position as a primary system of the body.

In a previous tutorial which I hope you've already had a chance to watch, we've already introduced the basic primary anatomy of the lymphatic system introducing you to structures such as the spleen, the thymus, the tonsils, and the thoracic duct. Today, I want to change our focus of attention just a little bit by giving you an introduction to the lymph nodes.

The lymphatic system has quite a unique makeup, that's for sure. You may remember from our introductory tutorial to the lymphatic system that we discussed how it is composed of two primary divisions – the lymphatic vasculature and the lymphoid organs – and don't forget to take a note of these two terms – lymphatic and lymphoid.

Lymphatics in general refer to the movement of lymph throughout the body while the term lymphoid refers more to the immune system-related functions – two terms which will often cause confusion. When we look at the major lymphatic vessels, we learned about structures such as the thoracic duct, the right lymphatic duct, and the cisterna chyli. Focusing on the lymphoid organs, you'll hopefully already know that we have primary and secondary lymphoid organs and tissues in our body.

The primary lymphoid organs, also known as central lymphoid organs, include the bone marrow and the thymus, both of which are involved in the production, maturation, and selection of immune-related cells such as T and B lymphocytes. The secondary lymphatic organs which are also known as the peripheral lymphatic organs are concerned with initiation of what's known as adaptive immune response and also serve as the site for lymphocyte activation. Examples of secondary or peripheral lymphoid organs include the tonsils, Peyer's patches, the spleen and, of course, the lymph nodes. And as I mentioned, today, we're going to be focusing specifically on our lymph nodes.

Did you know that we can have up to eight hundred of these lymph nodes in our body? Yep, you heard me – eight hundred lymph nodes. Obviously, I won't be able to introduce all of the lymph node groups today, however, I'll do my best to explain what exactly is a lymph node followed by an introduction to lymph nodes by region of the body beginning with the head and the neck, the thorax, the abdomen and pelvis, the lower limbs and, finally, the upper limb.

The term node comes from the Latin “nodus” which refers to a knot which is exactly how these structures appear. They are described as being intercalated along within the lymphatic system, meaning that they appear in groups or chains of nodes along the lymph vessels, just like knots along a piece of rope.

Lymph nodes vary in their shape, size, and number. Their shape can be round, oval, spindle-like or kidney-shaped. Size is determined by several factors such as inheritance, age, functional load, and number of nodes in a lymph node group. Abnormally large nodes are often indicative of pathological changes, but we'll discuss that in much more detail later in the tutorial.

As I mentioned, the total number of lymph nodes is estimated to be approximately six hundred to eight hundred, however, this is quite variable due to factors such as the size and the sex of an individual. Let's take a moment to look at this simple illustration of a lymph node.

So lymph is conducted to the nodes via afferent vessels and from the nodes via efferent vessels. The afferent vessels can be either peripheral collectors leading from a collection area to the lymph nodes or they can be internodal connective branches draining from other lymph nodes. The afferent vessels may enter the node at almost any point of the nodal surface which is the outer convex surface of the lymph node while the efferent vessels leave the node only at the hilum. The efferent vessels are therefore fewer in number than the afferent as well as being thicker and containing more valves.

The blood vessels also enter and leave the lymph node at the hilum. The lymph node itself is surrounded by a capsule consisting of densely-packed collagen fibers as well as a few elastic fibers. Trabeculae reach out from the capsule towards the center and form incomplete divisions within the lymph node. The basic lymph node is formed from reticular connective tissue which contains many lymphocytes and these are more tightly packed around the periphery which is known as the cortex. Deep to this is the medulla which is more loosely packed and organized into medullary strands, and there's no clear border between the cortex and the medulla.

So now that we've explored some of the microanatomy of a lymph node, let's now move on and have a look at some of the better-known lymph nodes of the body, beginning with the region of the head and neck.

Of the approximately eight hundred lymph nodes in the body, three hundred or more than one-third of all nodes are located in this region which makes this region complex, to say the least. And the primary reason for the amount of nodes located here is to provide a sort of surveillance system over all kinds of pathogens which might be ingested or inhaled by the oral and nasal cavities. We'll be keeping it pretty general today and taking time only to identify some of the most common node groups which are good to be aware of.

Most of the regional lymph nodes of the head are located at the boundary of the head and the neck region and these nodes are known to belong to the pericervical lymphatic circle or collar. The facial lymph nodes are located above these nodes in the facial region and other nodes such as the lingual lymph nodes are located within the pericervical circle.

I'm only going to speak about two node groups of this head region which are perhaps the most commonly known of this region. The first group are the submandibular lymph nodes which are a group of three to six lymph nodes located mainly around the submandibular gland. Afferent vessels of the submandibular lymph nodes receive lymph from the submandibular gland, the sublingual gland, the bottom of the oral cavity, the tongue, the gingiva, the teeth, the lips, as well as parts of the nasal cavity, the eyelids, and the chin.

The submandibular nodes commonly become swollen or tender due to infections of the teeth, the upper respiratory tract, the sinuses, and the tonsils. When this occurs, you often might hear this being incorrectly described as someone having swollen glands. The submandibular nodes may also become enlarged due to metastatic disease such as malignant growths in the submandibular and parotid glands and as well as the oral cavity.

The submental lymph nodes are located within the submental triangle which is an area below the chin overlying the mylohyoid muscle and the submental nodes drain lymph coming from the chin, the middle part of the lower lip, and the cheeks, deep vessels come from the gingiva, and the anterior part of the oral cavity.

Continuing down into the neck or cervical region now, we have two main groups of cervical lymph nodes, which are the anterior cervical lymph nodes and the lateral cervical lymph nodes, and as you would expect, the anterior cervical lymph nodes are located along the anterior aspect of the neck in what's known as the infrahyoid region and they consist of two groups – the superficial and deep anterior cervical lymph nodes. And examples of such include the pretracheal and prelaryngeal nodes which are located anterior to the trachea and the larynx respectively.

The lateral cervical lymph nodes are located along both lateral aspects of the neck and like the anterior cervical nodes, they can be divided into two groups – the superficial and deep lateral cervical lymph nodes. And these groups are then again further subdivided based on their specific locations. Collectively, the lateral cervical lymph nodes are numerous and receive lymph from most of the more superior lymph nodes of the head, and they form an intercalated pathway which reaches along the length of the internal jugular vein and surrounding structures right down to the clavicle where we have the supraclavicular lymph nodes which are of great clinical importance. And stay tuned, we'll find out exactly why they're so important later on.

So let's move on now from the cervical region and turn our attention now to the nodes of the thoracic cavity. The lymph nodes of the thoracic cavity can be roughly divided into two main groups – the parietal thoracic nodes which refer to the lymph nodes of the thoracic wall and the visceral thoracic nodes which are located around the organs of the thorax. The visceral thoracic nodes are largely comprised of a large group of nodes which are known as the mediastinal lymph nodes, and the mediastinal lymph nodes can be divided into anterior and posterior mediastinal lymph nodes which is separated by a third intermediate group known as the tracheobronchial lymph nodes.

The anterior mediastinal lymph nodes which include the brachiocephalic lymph nodes and the prepericardial lymph nodes are found anterior to the brachiocephalic veins and the pericardium respectively and these receive lymph from the thymus, the thyroid gland, the pericardium, as well as the heart.

The tracheobronchial lymph nodes are a large collection of lymph nodes which are located around the trachea and bronchi of the lungs as well as within the lungs themselves. To learn more about these specific lymph nodes, don't forget to check out one of our other video tutorials where we discuss in more detail the lymphatics of the lungs.

Okay, so let's continue on with our lymph nodes, and we're now moving into the posterior mediastinum where we have the appropriately named posterior mediastinal lymph nodes. And these are located in the region posterior to the hilum of the lungs and the pericardium, the superior surface of the diaphragm, anterior to the descending thoracic aorta which I've drawn in for you as well as lateral to the esophagus – and you can see the nodes highlighted on this illustration in green. The posterior mediastinal nodes drain lymph away from the esophagus, the posterior pericardium, and the posterior surface of the diaphragm.

Continuing inferior to the thorax, we now reach the abdomen where there are quite literally hundreds of lymph nodes associated with various viscera or organs as well as adjacent to the main vascular structures within the region. An example of these would be the mesenteric lymph nodes which drain a large portion of the small intestine.

The superior mesenteric lymph nodes form one of the largest groups of lymph nodes in the body and consists of somewhere between one hundred and one hundred and fifty lymph nodes dispersed throughout the mesentery which is the extensive peritoneal folding that attaches the small intestine to the abdominal wall. We can roughly divide this large group of lymph nodes into three subgroups which are the peripheral or juxtaintestinal lymph nodes consisting of small nodes located adjacent to the most peripheral blood vessel arches, the larger intermediate mesenteric lymph nodes which are located along the length of the jejunal and ileal arteries, and finally the superior central lymph nodes which form a chain along the superior mesenteric artery and the vein in the root of the mesentery.

The central nodes, therefore, form the major collecting point for the lymph of the small intestine but also for the inferior parts of the pancreas and parts of the large intestine. Efferent collectors of the central mesenteric lymph nodes may empty into the intestinal lymph trunk which then discharges into the cisterna chyli but, however, this is highly variable.

Okay, so we're going to continue inferiorly down into the pelvis specifically to the region surrounding the common, external and internal iliac arteries where we can find the aptly named iliac lymph nodes. Like their associated arteries, these lymph nodes can be subdivided into common, external, and internal groups and receive lymph drained from the areas supplied by these arteries which means just how the common iliac artery is the root artery for all arteries of the lower limbs and the most pelvic organs, the common iliac lymph nodes similarly receive lymph drained from these regions also.

Moving a little more inferior on our main illustration towards the lower limb, another group of lymph nodes which I'd like to introduce you to are the superficial inguinal lymph nodes. As you can see in the illustration, the superficial inguinal lymph nodes are found on either side of the groin region and form two groups – a proximal or horizontal group and a distal or vertical group.

The superficial inguinal nodes usually consist of about ten to twelve nodes and are embedded within the subcutaneous fatty tissue of this region which is why they are normally only palpable in persons who are relatively thin. The superficial inguinal lymph nodes receive lymph from the superficial lymph vessels of the lower limb except those from the posterolateral leg and the sole of the foot. Efferent lymph vessels drained from the superficial inguinal nodes continue to the external lymph nodes which we identified earlier.

Not visible in our main image but worth mentioning all the same are these nodes which are the deep inguinal nodes, and generally, there can be between one to three deep inguinal nodes which are found medial to the femoral vein. They receive afferent vessels from deep lymph vessels that accompany the femoral vessels, lymph vessels from the glans penis or clitoris, and a few efferents from the superficial inguinal nodes, and the efferent vessels of these nodes also drain to the external iliac nodes.

Another group of lymph nodes in the lower extremity are the popliteal lymph nodes, and these are a group of nodes which are found within the fatty tissue around the popliteal fossa along the posterior aspect of the knee joint and generally number six or seven nodes. One of the popliteal lymph nodes known as the superficial popliteal node lies at the point where the short saphenous vein joins the popliteal vein and drains the superficial regions of the lateral leg and the sole of the foot.

The deep popliteal lymph nodes are situated around the popliteal vessels receiving trunks that accompany the anterior and posterior tibial lymphatic vessels. Most of the efferent popliteal lymphatic vessels ascend close to the femoral vessels to reach the deep inguinal nodes, however, some may accompany the great saphenous vein to the superficial inguinal nodes.

And last but not least, we're going to look at the lymph nodes of one final region of the body which is the upper extremity. As you can see in the illustration, many of the lymph nodes of the upper limb are concentrated in and around the armpits or the axilla and these are known as the axillary lymph nodes.

The axillary lymph nodes are a large group of approximately twenty to thirty nodes which are generally subdivided into five groups, and these are the anterior or pectoral group which drain the skin and the muscles of the anterior and the lateral walls of the trunk above the umbilicus and the lateral parts of the breast; the posterior or subscapular group which receives lymph from the muscles and the skin of the back from the scapula area down to the iliac crest; the lateral or brachial group which drains the lymph from the superficial and deep compartments of the upper limb except for the superficial vessels of the arm that run along the cephalic vein; the central group which receives the efferent vessels of the three groups previously mentioned; and finally, the apical group which also drains lymph from the other axillary nodes as well as lymph drained directly from some superficial vessels running along the cephalic vein.

Efferent vessels of these axillary nodes unite to form the subclavian trunk which then opens into the right lymphatic duct on the right side or into the thoracic duct on the left side, and the most common cause malignant axillary lymph node enlargement is breast cancer.

Continuing distally along the upper limb, we also have another small group of lymph nodes known as the cubital lymph nodes and the nodes mainly refer to the supratrochlear nodes, also known as the epitrochlear or the supraepicondylar nodes which are located close to the medial epicondyle of the humerus. And other cubital nodes may be located distal to the elbow joint close to the common interosseous artery. Cubital nodes receive lymph drained from superficial portions of the ulna and forearm as well as the middle, ring, and little fingers.

And that concludes our introduction to the major lymph nodes to the body. Before we conclude, let's discuss some clinical correlations to this topic.

Lymphadenopathy refers to a series of diseases or conditions which affect our lymph nodes resulting in them becoming abnormal in size, hard or rigid or increasing in number. Lymphadenopathy can be localized, meaning restricted to just one area of the body, or generalized, which means it affects lymph nodes in several different regions. The vast majority of occurrences of lymphadenopathy are not serious and are most often related to infection which can also be referred to as lymphadenitis. These are your typical acute viral or bacterial infections which you might get from a tooth infection or when battling the flu. Generally, these are short-lived and they last for one to two weeks only.

More chronic infections such as tuberculosis lymphadenitis, cat-scratch disease or toxoplasmosis, and even bubonic plague. More serious cases of lymphadenopathy include those related to cancer and this may develop within the lymph nodes themselves such as in the case of either Hodgkin’s or non-Hodgkin's lymphoma and it may have alternatively spread to the other lymph nodes from other tissues drained in the body which is known as metastatic cancer. Another serious causes of lymphadenopathy may be related to immune diseases such as lupus and HIV.

And with that, we have completed our introductory tour to the lymph nodes of the body. Let’s do a quick recap of what we've explored today before we finish up.

So we began with the head and the neck where we focused on three major groups of lymph nodes which included the submandibular lymph nodes draining the teeth, gingiva, and inferior half of the oral cavity; the submental lymph nodes which drain the anterior oral cavity, inferior lips and chin region; and finally, the cervical lymph nodes which we saw were comprised of anterior and lateral groups.

Moving onto the thorax, our lymph node group of interest was the mediastinal lymph nodes which again could be subdivided into superior, anterior, middle, and posterior groups. Continuing inferiorly, we explored some of the abdominal lymph nodes, in particular, the vast superior mesenteric lymph node group. After that, we moved into the pelvic region where we discussed the iliac nodes and here we learned that this group can be further subdivided into common, external, and internal iliac lymph nodes. In this region, we also looked at the inguinal lymph nodes located at the region of the groin which are comprised of the superficial and deep groups.

Continuing into the most distal part of the body, the lower limb, we found this region to be relatively sparse of lymph nodes, but we did however briefly discuss the popliteal lymph nodes which are located in the popliteal fossa posterior to the knee joint. And finally, our last region of interest was the upper limb where we explored two major groups of lymph nodes. The first was the axillary lymph nodes which are the well-known node group of the axilla or armpit, and last but not least, we discussed the cubital lymph nodes which are generally located in the region of the elbow joint.

And that's it, we're done and dusted.

I hope you enjoyed your introduction with some of the major lymph node groups of the body. Remember if you wish to explore the lymph node groups of a particular region of the body in more detail than what we discussed today, you’ll be able to find dedicated videos for this on our website.

Thanks for watching. Happy studying!

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