Lymph nodes and lymph vessels, including those found in the lungs, are part of the body's immune system, and they transport waste material and fluids from tissues throughout the body, states the American Cancer Society. The liquid they transport is called lymph fluid, which contains oxygen, nutrients, viruses and white blood cells.
There are hundreds of lymph nodes located throughout the body, according to the American Cancer Society. These nodes act as filters for harmful materials such as bacteria and contain cells that help fight infection by targeting and attacking germs as they travel through the lymph fluid. Each lymph node filters substances carried to it from the vessels, and the fluid then moves toward the chest. After reaching the chest, the filtered lymph fluid, salts and proteins re-enter the bloodstream.
When lymph nodes run into problems such as injury, infection or cancer, they may expand or swell as they attempt to clear out the problem cells, the American Cancer Society says. Lymph nodes commonly swell in the neck, groin and underarms. Generally, only one area swells at a time. However, certain infections, medicines, immune system diseases or cancers may cause more than one lymph node area to swell at the same time.