Swollen lymph nodes in your neck are one way to know if you have a cold. They swell because they’re busy fighting the invading virus.

Those nodes—points of filtration and cell multiplication—are part of the lymphatic system, which includes tissues, organs, and vessels scattered throughout the body. Other than killing infectious agents, the lymphatic system also maintains the fluid balance in the blood and absorbs fats from the digestive tract.

The parts of the lymphatic system are named after the area of the body in which they are found. For example, the nodes in the neck are called cervical nodes (after the cervical part of the vertebral column) and mandibular nodes (after the mandible, or jawbone).

The vessels transport a fluid called lymph. It’s similar to blood plasma. It contains disease-fighting white blood cells, specifically lymphocytes, a type of white blood cell. There are three kinds of lymphocytes:

  • NK cells: Called “natural killer” cells, these play a large role in defending the body against viruses and tumors.
  • T cells & B cells: Made in the thymus and bones, respectively, these white blood cells target specific pathogens or infected cells. Both create antibodies that “remember” the pathogen and are prepared to mount a defense against it should the body ever encounter it again.

The vessels and lymph create a one-way system that interacts with the circulatory system at capillaries, permeable vessels that allow for the lymph and circulatory systems to interact as lymph enters the bloodstream. Similar, yet not identical, capillaries exist in the lungs where blood receives oxygen.

Other important parts of the lymphatic system include:

  • Thymus: Some lymphocytes mature in this small butterfly-shaped organ in the chest.
  • Tonsils: Located in the throat, these masses of lymphoid tissue remove contaminants that come in contact with the body through the mouth.
  • Appendix: Attached to the large intestine in the lower abdomen, this finger-like tube’s function is widely unknown, but some theories believe it helps keep dangerous contaminants from invading deep tissue in the organs.

However, both the tonsils and appendix can be removed if they become infected with bacteria and become enlarged. Still, the body can function without either of these organs.

The lymphatic system plays an important part in cancer diagnosis in that the seriousness of the cancer is determined by whether or not it has spread to the lymph nodes. Also, patients who begin treatments before cancer has spread to the lymph nodes have a greater chance of survival because the cancer has not infected this vital system.