Lymphatic System
Directions
- Print this PDF worksheet for a hardcopy guide as you work through this lesson.
- Within the lesson click the red linked headings to bring up the desired starting point within the cadaver for your work.
- Use the provided images on the worksheet to annotate and identify specific anatomical structures.
As you see, the lymphatic system is a bit like the cardiovascular and nervous systems, it branches throughout the body. In this dissection we'll examine a few discrete lymphatic organs, however, the lymphatic vessels are too delicate (thready) to survive the dissection process of our specimen.
The lymph trunks and ducts are WAY too small to see in our specimen. Lymph collected in these capillaries empties into one of the principle lymphatic trunks, lumbar, intestinal, bronchomediastinal, subclavian, and jugular. As you hopefully surmise, these trunks are larger than the capillaries and are named for their locations. Again, they are simply to thready to be observed in our specimen. The lymphatic trunks empty into two main lymphatic channels.
- Thoracic Duct (left) - The thoracic duct is about 38-45 cm long and begins as a dilation at its inferior end called the cisterna chyli. This is the main duct for the return of lymph to the blood. The cisterna chyli receives lymph from the lumbar and intestinal trunks. One of the larger abdominal expansions you see here is undoubtedly the cisterna chyli, it just isn't labeled separately in your specimen. In the neck, the thoracic duct receives lymph from the trunks draining the left side of the head, neck, chest, the left upper limb, and the entire body inferior to the ribs. The thoracic duct drains into the left internal jugular and left subclavian veins.
- Right Thoracic Duct - As you can see, this right lymphatic trunk is only about 1.2 cm long. It receives lymph from the right jugular, subclavian, and bronchomediastinal trunks which drain the upper right side of the body. The right thoracic duct drains into the right jugular and right subclavian veins.
Red bone marrow (in flat bones and adult long bone epiphyses) and the thymus are primary lymphatic organs because they are where stem cells divide and become "immunocompetent" meaning that they are capable of mounting an immune response. The lymph nodes, spleen, and lymphatic nodules are where most immune responses occur and are called secondary lymphatic organs and tissues.
- Thymus - The thymus generates several cell types that are involved in our immune responses. The thymus' primary job is populating secondary lymphatic organs with T-cells early in life. Beginning at puberty, the thymus begins to atrophy and is quite small once we reach old age.
- Lymph Nodes - As you can see, lymph nodes are scattered throughout the body but do occur in several concentrations, too.
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Spleen - The spleen is the largest single mass of lymphatic tissue in the body. Rotate your specimen to a lateral perspective so you can see the depth of this organ. Of course, realize you are looking THROUGH the arm :-). Blood flows into the spleen (via the splenic artery) where B cells and T cells carry out immune functions similar to what occurs in lymph nodes. Splenic macrophages also destroy blood-borne pathogens by phagocytosis. Three blood related functions also occur within the spleen:
- Macrophages remove worn out or defective blood cells and platelets.
- Platelets are stored (up to 1/3rd of the body's supply).
- Blood cells are produced during fetal life.
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Lymphatic Nodules - Because lymphatic nodules are NOT encapsulated they are considered lymphatic "tissues" rather than organs. This lateral perspective gives you an idea of the depth of these nodules, however, the anterior perspective provides you with a better look at their distribution. Rotate your specimen back to the anterior position.
- Pharyngeal Tonsils (Adenoids)
- Palatine Tonsils - commonly removed in a tonsillectomy
- Lingual Tonsils - sometimes removed during a tonsillectomy
- Peyer's Patches (not specifically labeled in your specimen) - Large isolated clusters of lymph nodules are found in the wall of the distal portion (ileum) of the small intestine and in the wall of the appendix. These tissues are structurally similar to the tonsils. These function to destroy bacteria that are present in large numbers in the intestine. This prevents pathogens from crossing the intestinal wall and entering the bloodstream. These tissues also generate many "memory" lymphocytes for long-term immunity.
Self-Test Labeling Exercises