Lymphatics are part of the body's immune system. They are bioactive filters that recognize and produce antibodies against infectious agents. They can also be breeding grounds for metastasizing cancer cells. Therefore, the organization of the lymphatic system informs us about the spread of disease and design of therapeutic approaches.
Although lymphatic vessels are too small to identify on the Visible Human, they often follow blood vessels. On the other hand, lymph nodes (highlighted green) are easily seen and widely distributed in the body. They are localized in groups as regional lymph nodes and connect in chains via lymphatic vessels such that upstream regions drain into downstream regional lymph nodes until the lymph reaches the left or right lymphatic trunks. Lymph nodes are located in the axillary and inguinal regions to gather lymphatic flow from the limbs. There are large groups of nodes around the digestive tract in the abdomen and around the trachea and bronchi in the thorax. Lymph nodes are also located in large numbers in the head and neck.
Note: Lymph nodes and ducts are small. Structures mentioned in the text are found in the crosshairs of the cross-sectional images. Toggle the planes on and off in the 3D image to see the location of each cross-sectional image. To help orient yourself to an anatomical region and enhance your understanding of the relationships, zoom in and out, rotate and vary the skin opacity of the 3D image.
In the axilla (arm pit), axillary lymph nodes (highlighted green; the rest are unhighlighted) follow the course of the axillary vessels. They drain lymph nodes from the upper limb and nearby regions of the chest wall. Use the slider accessed by the "skin" icon at the bottom left of the 3D view to adjust the skin to 60% opacity. Confirm which nodes are in the arm and which are in the chest wall by examining the cross-sectional images and rotating the 3D image. Not shown here, most of the mammary gland drains into axillary lymph nodes. Axillary lymph nodes drain into the venous system by the main or right thoracic ducts. The ducts are highlighted brown and will be found in the crosshairs of the cross-sectional images. Termination of each duct is found where the jugular meets the subclavian vein. Mouse over the image until the labels for these structures appear. The main duct (on the left) is dilated and appears much larger than the right duct.
Within the chest, lymph nodes are located along the bronchopulmonary tract. These mediastinal lymph nodes drain the lungs and heart. Mediastinal nodes then drain into tracheal lymph nodes and then the thoracic duct.
The largest lymphatic vessel, the thoracic duct, lies in the posterior mediastinum between the aorta and the azygos vein. See the small brown profile to the right of the aorta in the cross-section. It drains the entire body except the right upper limb, right side of the head, and the upper right quadrant of the chest which all drain into the right thoracic duct.
The thoracic duct drains abdominal lymph nodes located along the aorta, arteries that supply the intestines, and alongside the intestines. All of these lymph nodes drain to nodes close to the aorta (para-aortic lymph nodes) before draining into the thoracic duct. Rotate the 3D image left and right. A good way to do this is to hold down the Ctrl (PC) or Command (Mac) Key and press the left/right arrows on the keyboard. Wait for the image to move before pressing the directional arrow again. Step through cross-sectional images by grabbing with your mouse and moving an image plane in the 3D view or by using the Ctrl or Command Key and the up/down arrows.
Within the pelvis and inferior abdomen, lymph nodes follow the iliac artery system. Lymph nodes within the pelvis lie along arteries in the pelvic walls. Pelvic lymph nodes drain into para-iliac lymph nodes, which drain into the para-aortic lymph nodes, which drain into the thoracic duct. Rotate the image to show that pelvic lymph nodes (green) are distinct from abdominal lymph nodes (brown). Note how the pelvic lymph nodes lie next to or posterior to the external iliac artery.
The para-iliac lymph nodes also drain the deep and superficial inguinal lymph nodes. These drain the skin of the genitalia and the lower limb. The superficial inguinal lymph nodes are located just inferior to the inguinal ligament along the course of the great saphenous vein (see cross-sectional images). Because there are no major arteries in the subcutaneous fat, lymphatic vessels course alongside veins instead.
All head and neck lymph nodes eventually drain into deep cervical lymph nodes that follow the course of the internal jugular vein and drain into thoracic ducts close to where the axillary lymph nodes drain. Deep cervical lymph nodes can be seen deep to the sternocleidomastoid in the cross-sections and 3D view (Visible Human's right side). Draining into the deep cervical lymph nodes there are submandibular lymph nodes, found in relation to the mandible, and several groups of lymph nodes running near the superficial veins. There are parotid lymph nodes lateral and posterior to the mandible and mastoid lymph nodes posterior to the ear.
Patterns of lymphatic drainage are important to the clinician. For example, to stage (determine how advanced) a cancer, one criteria is to determine if lymph nodes are involved. The clinician needs to know where to look for potentially positive lymph nodes. Consider the following questions.
Would lymph nodes in the hand and mammary gland eventually drain into a common set of lymph nodes? Which ones?
Yes, lymph from both locations would drain into axillary nodes before returning to the blood stream via a thoracic duct.
Would lymph nodes under the chin and mammary gland eventually drain into a common set of lymph nodes? Which ones?
No, lymph from under the chin would drain into cervical nodes, which do not communicate with axillary nodes.
Would lymph nodes in the lung and mammary gland eventually drain into a common set of lymph nodes? Which ones?
No, lymph from the lung would drain into bronchopulmonary nodes, which do not communicate with axillary nodes.
A patient with no history of inguinal or scrotal surgery has testicular cancer. Where would you expect to find cancer-containing lymph nodes: Inguinal nodes, iliac nodes, and/or aortic nodes?
Aortic nodes. Except for the superficial drainage of the limbs, lymphatics course alongside arteries. The testes are supplied by the testicular arteries, which branch off the aorta just inferior to the renal arteries. Accordingly, inguinal and iliac nodes would be bypassed. In contrast, the scrotum would drain to inguinal nodes. Surgery can alter the pattern of lymphatic drainage.
Review the distribution of lymph nodes and follow lymph back to the thoracic ducts. Which lymph nodes drain into nodes that drain into nodes that drain directly into a thoracic duct?