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, the lymph nodes (labeled green) are easily seen and widely distributed in the body. They are localized in groups as regional nodes. Regional nodes are organized in chains such that upstream regions drain into downstream regional nodes until lymph reaches the left or or right lymphatic trunks. 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 track in the abdomen and around the trachea and bronchi. Nodes are also located in large number in the head and neck. Lymphatics often follow blood vessels.
Note: Lymph nodes and ducts are small. Structures mentioned in the text are found in the cross hairs of the sectional images. Toggle the planes on and off in the main image to see where each sectional image was taken. To get your orientation, feel free to zoom in and out or to rotate the images.
In the axilla (arm pit), axillary nodes (labeled green; the rest are now brown) follow the course of the axillary vessels. They drain nodes from the upper limb and nearby regions of the chest wall. Use the right slider on the bottom of the right window to add back the skin to 60% opacity. Confirm which nodes are in the arm and which are in the chest wall by examining the sectional images and rotating the main image. Not shown here, most of the mammary gland drains into axillary nodes. Axillary nodes will drain into the venous system by the main or right thoracic ducts. The ducts are labeled brown and will be found in the cross hairs of the sectional images. The ducts are found where the jugular vein 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, nodes are located along the bronchopulmonary tract. These mediastinal nodes drain the lungs and heart. The nodes then drain into tracheal 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 limb, right side of the head, and the upper right quadrant of the chest. Those structures drain into the right thoracic duct.
The thoracic duct drains abdominal nodes, located along the aorta, arteries that supply the intestines, and alongside the intestines. Rotate this image left and right. A good way to do this is to hold down the Ctrl (PC) or Command (Mac) Key and then the left/right arrows on the key board. Wait for the image to move before hitting the directional arrow again. Step through the sectional images by grabbing an image with your mouse or by using the Ctrl or Command Key and the up/down arrows. All of these nodes drain to nodes close to the aorta (para-aortic nodes) before draining into the thoracic duct.
Within the pelvis and inferior abdomen, nodes follow the iliac artery system. Nodes within the pelvis lie along arteries in the pelvic walls. Pelvic nodes drain into para-iliac nodes, which drain into the para-aortic nodes, which drain into the thoracic duct. Rotate the image to show that the pelvic nodes (green) are distinct from the abdominal nodes (brown). Note how the pelvic nodes lie next to or posterior to the external iliac artery.
The para-iliac nodes also drain the deep and superficial inguinal nodes. These drain the skin of the genitalia and the lower limb. The superficial inguinal nodes are located just inferior to the inguinal ligament along the course of the great saphenous vein. See sectional images. Because there are no major arteries in the subcutaneous fat, lymphatics course alongside veins instead.
All of these nodes eventually drain into deep cervical nodes that follow the course of the internal jugular vein. These nodes drain into the thoracic ducts close to where the axillary nodes drain. Deep cervical nodes can be seen deep to the sternocleidomastoid in the cross section and in the main window (visible human's right side). Draining into the deep cervical nodes there are submandibular nodes, found in relation to the mandible, and several groups of nodes running near the superficial veins There are parotid nodes lateral and posterior to the mandible and mastoid 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 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 being returned 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?