What is the Lymphatic System, and What Does it Do?

Most patients have heard of the lymphatic system, but few understand exactly what it is, what it does, and why it is important for their overall health. The lymphatic system controls fluid levels throughout the body and is also a primary part of the immune system.

Overall, lymphatic health helps other systems throughout the body work better, including the cardiovascular and gastrointestinal systems. It can also be a key player in fighting infections and some cancers. This article provides an overview of the lymphatic system and its role in the body.

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What is the Lymphatic System?

The lymphatic system is part of the immune system. It plays a primary role in defending the body against infections and keeping body fluid levels in balance. Lymphatic vessels, tissues, organs, and glands (Figure 1) drain a watery fluid called lymph from throughout the body.

Key components and their roles:

• Lymphatic vessels, similar to blood vessels, are found throughout the body. However, they carry a clear fluid called Lymph (Latin for Water) instead of blood. This fluid contains lymphocytes (white blood cells) and helps regulate infections.
• Bone marrow is the thick, spongy, jelly-like material found inside bones. It makes many kinds of blood cells, including red blood cells and immune system cells.
• The thymus gland, which sits between the lungs and just above the heart, makes specialized immune system cells called T cells. This occurs primarily before and during puberty.
• Tonsils sit at the back of the throat and help fight infection and disease. They help filter germs and toxins that enter the mouth and nose.
• The appendix is a small pouch-like organ at the end of the large intestine. While humans no longer need this organ, and its exact purpose is unknown, it seems to be part of the lymphatic system, acting as a post-digestion filter for bacteria and other harmful substances. It can, at times, get blocked and inflamed with bacteria, causing appendicitis.
• Lymph Nodes are small, bean-shaped structures that filter lymphatic fluid. They contain concentrations of white blood cells to help the body fight infection and disease. There are hundreds of lymph nodes throughout the body, with clusters in the neck, axilla (underarm), chest, abdomen, and groin.
• The spleen is a small organ inside the rib cage, just above the stomach. It stores and filters blood and makes white blood cells.
• Adenoids are small organs behind the nasal passage that trap germs entering the body through the nose and mouth. Adenoids begin to shrink around age 5 and usually disappear by adulthood.

The lymphatic system's primary function is to balance the fluid volume in the body and carry it to the circulation for elimination by the kidneys. The lymphatic system eliminates excess protein molecules, microorganisms, and foreign particles when it does this. It carries antigens and leukocytes to lymph nodes, where immune cells are located. 

In addition, the system can absorb fat-soluble vitamins and fatty substances in the gut via the gastrointestinal tract.

Recently, lymphatic vessels have been discovered near the spine and brain, which are believed to help keep the cerebrospinal fluid clean and uninfected. They may help prevent neurological disorders such as multiple sclerosis, meningitis, and Alzheimer’s disease.

Functions of the Lymphatic System

The lymphatic system has several functions related to health and the stability (homeostasis) of the human body. The system helps maintain the body's stability in cellular and large organs. Those functions can be divided into four primary categories. 

• The lymphatic system's main function is maintaining fluid levels in the body. During normal daily functioning, fluids leak between cells and organs and can build up in interstitial spaces. Those fluids would usually become trapped and cause swelling and discomfort. The lymphatic system pumps that fluid out of those trapped spaces and into the vasculature to be removed.
• Another purpose of the lymphatic system is to help fat and fat-soluble nutrients. Like the interstitial fluids, these fats normally have difficulty entering the body. The lymphatic system absorbs these molecules, even against pressure gradients, and allows them to pass into the body’s circulatory system for transport and use.
• Lymph nodes monitor the lymph flowing into them, and when they detect infection or disease, they produce T-cells and antibodies to fight the disease or infection.
• The lymphatic system removes toxins and impurities from the body, such as carbon dioxide, sodium, and cellular byproducts, through perspiration, bowel movements, urine, and exhalation.

The lymphatic system works mainly through pressures between lymphatic fluids and the vasculature. For impurities, extracellular proteins, antibodies, and the rest to pass through, there has to be a higher pressure within the lymph systems than in the vasculature.

The lymphatic system interacts with the small capillaries, where pressures are reduced, to allow these items to flow into the bloodstream for removal. These small lymph capillaries interact with blood capillaries. The tissues' fluid enters the lymph capillaries and is drained away (Figure 2). These fluids, termed lymph, also contain many white blood cells.

Conditions and Disorders of the Lymphatic System

The most common issue in the lymphatic system is lymphadenopathy, or swollen lymph nodes. Common infections, like strep throat, infected wounds, or mononucleosis can cause enlarged lymph nodes. Even a simple cold or the flu can cause swollen lymph nodes, especially the ones in the neck. This is why palpating (feeling) the throat nodes is a common practice in medicine.

There are also specific lymphatic disorders, including:

• Lymphedema is swelling that results from the build-up of lymph fluid in the fatty tissues just under the skin. Lymphedema can be caused by a variety of diseases, as well as direct damage to the lymphatic system. It occurs most commonly in the arms and lower legs. Signs of lymphedema include:
  • Swelling, fullness, or heaviness in the breast, chest, shoulder, arm, hand, leg, or foot
  • Skin changes such as dryness, discoloration, thickening, or dimpling
  • Aching, tingling, numbness, pain, or discomfort
  • Loss of flexibility in the joints
  • Trouble putting clothes on, feeling clothes are tighter.
• Castleman Disease is a group of rare disorders affecting the immune system similar to the flu or infection but without an infection being present. This disorder affects about 5,000 people per year in the United States. It creates an overactive immune response that can be damaging, even deadly if left untreated.
• Lymphoma is a serious type of immune system cancer that should be immediately evaluated and treated by a team of physicians.
• Any type of cancer can cause a disorder of the lymphatic system, as the immune system works overtime to deal with any type of cancer in the body. Any cancer treatment plan should involve monitoring the lymphatic system.

Testing and Diagnosis

Tests to check the health of the lymphatic system include a complete blood count (CBC) and palpation of the lymph nodes. If a lymphatic disorder is indicated, a clinician may order more extensive testing, such as a CT scan or MRI.

In addition to the standard tests, a clinician might order a lymphoscintigram. This is a specific test designed to examine the lymphatic system's flow. The patient is injected with a radioactive dye that can be tracked by a scanner, showing how the dye moves through the lymphatic system to check for blockages.

Another advanced test is the Lymphocyte MAP test by Cyrex Labs, a newly developed test that measures several factors in the immune system, including lymphatic system health and its connection to the immune system.

Maintaining a Healthy Lymphatic System

Like any part of the body, diet, exercise, and lifestyle can affect the lymphatic system. It is important to ensure a healthy lifestyle includes steps to keep the lymphatic system flowing freely.

How can I keep my lymphatic system healthy?

• A lymphatic-friendly diet should include fruits and vegetables, especially those high in antioxidants such as blueberries, lean meats such as salmon and chicken, and seeds and nuts.
• Exercise encourages fluid to drain into the lymphatic system, specifically the abdomen, where it can be more easily cleared. Walking, swimming, and low-impact exercises such as Tai Chi are ideal for lymphatic help.
• Deep breathing exercises are a great way to help the lymphatic system work properly. The deep, slow movements of the diaphragm are beneficial to overall lymphatic flow and health.
• Proper hydration through water is key to keeping lymph fluids smooth and flowing freely. 

When to Seek Medical Advice

Contact a healthcare provider if any of these symptoms persist:

• Fatigue (extreme tiredness)
• Swollen lymph nodes may be a sign of common infections (like strep throat) or more serious conditions like cancer or HIV.
• Unexplained swelling that lasts more than a few weeks or interferes with your daily activities

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Key Takeaways

The Lymphatic System includes:

• Thymus
• Adenoids
• Spleen
• Tonsils
• Appendix
• Lymph Nodes

In addition, these organs interact with parts of the cardiovascular, digestive, and immune systems. It interacts with these systems to:

• Maintain the body’s fluid balance
• Maintain homeostasis
• Keep the immune system operating at peak efficiency

Understanding lymphatic health should be an important part of any patient’s overall health plan.  

All patients should be encouraged to maintain their lymphatic health through:

• Proper nutrition, such as blueberries and other foods high in antioxidants.
• Exercise, especially low-impact, full-body movements such as walking.
• Lifestyle changes, such as deep breathing exercises and proper hydration.

By keeping the lymphatic system healthy and operating at peak performance, patients can have another powerful tool in their quest to stay healthy, happy, and productive.