Lymph nodes are tiny, round (or bean-shaped) structures distributed throughout your body. They serve as biological filters of a sort, helping to trap and eliminate potentially dangerous germs, such as bacteria or viruses, which might otherwise do you harm. In some places—such as under the arms, in the groin, and in the neck—they cluster in groups. You may even be able to feel them if you try. In most cases, we are unaware of these structures. But when a problem develops and a node or nodes become swollen, it may be possible to feel one of these pebble-like structures beneath the skin.
Together with the lymphatic vessels and associated organs like bone marrow and the thymus gland, plus the lymph fluid, they comprise the lymphatic system. The lymphatic system is a key component of your body’s immune system.
The Parallel Circulatory System
The lymphatic system roughly parallels the more familiar blood circulatory system. Unlike the blood circulatory system, though, the lymphatic system has no central pump to continually force lymph fluid to circulate—sometimes against the pull of gravity—throughout the entire body. Also unlike the blood circulatory system, the lymphatic system is not “closed”.
Rather, clear, protein-rich, watery fluid (interstitial fluid), which bathes the spaces between the body’s cells, is free to drain into the system as needed to maintain proper fluid balance within the tissues. This fluid derives, primarily, from the blood itself. Most are drained back into the blood circulation, but up to three liters of this plasma-like fluid remains within the tissues. It’s the job of the lymphatic system to help drain this excess and keep fluid levels balanced.
Due to the lack of a central pump, the lymphatic system relies heavily upon passive assistance from the skeletal muscles surrounding given lymph vessels. The vessels in the ankles and legs, for example, must move lymph fluid against gravity to drain extracellular fluid back towards the heart for recirculation. A series of back flow-preventing valves, combined with contractions from walking, running or otherwise exercising your legs, help move the fluid northwards. In some instances, the lymph vessels themselves may contract rhythmically to assist in moving fluid within the vessels back towards the heart.
For those who are affected by lymphedema, the regular flow of lymph throughout the body is hampered, which means that external forces may be needed to help regulate. Compression garments that are specifically designed to facilitate the natural movement of lymph throughout the body are a common option. By working with their doctors to find the appropriate garments, patients can ease the symptoms of lymphedema.
Key Immune Functions
Lymph fluid (or simply; lymph), is a clear, watery fluid populated with specialized cells known as lymphocytes, as well as macrophages, which serve as a sort of clean-up crew that recycles waste material. The lymphocytes are warrior cells of the immune system. Divided between B lymphocytes and T lymphocytes, these cells cluster within the lymph nodes and stand vigil, waiting to trap and destroy any foreign cells. T cells are the vanguards of the adaptive immune system. T and B cells are specialized subtypes of white blood cells.
The adaptive immune system is a subset of the overall immune system. It features the ability to identify, “remember,” and destroy (or prevent the growth of) foreign invaders, such as bacteria. It is this aspect of the immune system that goes to work when we receive vaccinations. T cells identify the (weakened or inactive) disease-causing germ present in the vaccine, then devise specific ways to thwart it.
More importantly, they “remember” that information, and store it against future incursions by similar invaders. In this way, vaccinations prepare our immune systems to rapidly deploy specifically tailored cells to fight off these invaders, should they ever be encountered again. This system is highly specific. The parallel innate immune system is not nearly so specific.
Rather, it attempts to destroy any and all invaders identified as foreign. It provides immediate defense but does not “remember” specific invaders after they are eliminated. It’s a bit like the difference between having an electric fence, which immobilizes anything and everything that comes up against it, versus having ninja security guards, roaming the area, seeking out specific invaders who may be trying to get under, over, or around the fence. Once located, these ninja assassins of the acquired immune system (T cells) stealthily deal a fatal blow to the intruders.
How Can I Tell if My Lymph Nodes are Swollen?
When we are perfectly healthy, most of us will be unable to feel our lymph nodes beneath the skin. But occasionally (usually in response to certain types of infection) they may become noticeable as tiny bumps; typically in the neck, groin, or in the armpits. In some instances, there will be little to no cause for concern. But the following should prompt a visit or call to your physician, as any one of these could signal a more serious problem.
- They continue to swell over time; more than two to four weeks should prompt you to seek attention.
- They become hard, rubbery feeling, and immobile.
- You have an accompanying fever, night sweats, or persistent, unexplained weight loss.
- They have appeared suddenly, inexplicably.
- They are tender or painful.
- They reach the size of a kidney bean or larger.