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When your pet is ill, it is often a sign that their immune system is working. The lymphatic system is one part of the immune system that plays a vital role in protecting your pet. It is a network of tissues, vessels, and organs that carry a colorless fluid called lymph through almost all body tissues. Details of this system include:

  • Lymph fluid: The lymph is composed of white blood cells, known as lymphocytes, that are one of the primary cells of the immune system.
  • Lymphocytes: Lymphocytes are types of white blood cell that make up the body’s immune defense system. These cells include T cells, B cells, and natural killer cells.
  • Lymph vessels: Lymph vessels carry lymph fluid away from tissue and back into circulation.
  • Lymph nodes: Lymph nodes are small organs found throughout the body. During an infection, T and B immune cells residing in the lymph nodes are trained to recognize the bacteria or virus causing the problem. They are then activated to go to the site of infection.
  • Related primary organs: The spleen, bone marrow, and thymus gland are the primary lymphoid organs.
    • The bone marrow is the site where most of the body’s immune cells begin their development, including white blood cells, red blood cells, and platelets. These are then sent out to the rest of the body.
    • The thymus is also a critical location for immune cell development. Here, T cells are specially trained to fight the disease. Most of this immune cell development happens before birth. Therefore, a damaged thymus can be removed without harm to the immune system.
    • The spleen largely acts to filter blood. It specifically filters out any damaged red blood cells or unwanted microorganisms that might cause harm to the body.

The circulation of the lymph through the body is like the circulation of blood. The lymphatic system generates an immune response to protect the body against infections (for example, viral and bacterial) and foreign microorganisms. It also destroys cancer cells, eliminates toxins, and removes waste products. Lymph spreads from small blood vessels and moves into spaces between cells to carry waste materials out.

There are hundreds of small structures called lymph nodes throughout your pet’s body. As lymph circulates, it traps bacteria, viruses, toxins, and waste before entering the lymph nodes. The lymph nodes then filter out any harmful material or infectious agents and return the lymph back to the bloodstream.

Appreciating how your pet’s lymphatic system works helps you determine what you should pay attention to, especially in the lymph nodes. If you come upon anything unusual, consult your vet. Swollen lymph nodes can result from many things, so it is best to have your pet checked to determine the cause and learn about potential treatment options.

The Pet Cancer Foundation’s Website Editorial team is comprised of veterinarians, veterinary oncologists, and veterinary technicians, as well as scientific writers and editors who have attained their PhD’s in the life sciences, along with general editors and research assistants. All content found in this section goes through an extensive process with multiple review stages, to ensure this extended resource provides pet families with the most up-to-date information publicly available.

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Keep Your Pets Healthy Editorial Team

Last Updated: October 20, 2022

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The following sources were referenced to write the content on this page:

Hsu, MC & Itkin, M 2016, ‘Lymphatic anatomy’, Tech Vasc Interv Radiol, vol. 19, no. 4, pp. 247-254.

Liao, S & Padera, TP 2013, ‘Lymphatic function and immune regulation in health and disease’, Lymphat Res and Biol, vol. 11, no. 3, pp. 136-143.

Randolph, GJ, Ivanov, S, Zinselmeyer, BH & Scallan, JP 2017, ‘The lymphatic system: integral roles in immunity’, Annu Rev Immunol, vol. 35, pp. 31-52.

Swartz, MA 2001, ‘The physiology of the lymphatic system’, Adv Drug Deliv Rev, vol. 50, no. 1-2, pp. 3-20

The Pet Cancer Foundation’s medical resource for pet owners is protected by copyright.

For reprint requests, please see our Content Usage Policy.