How the Lymphatic System Works

The lymphatic system works with the cardiovascular system to maintain the balance of fluid in your body. Both systems supply the body’s tissues and organs with nutrients and also remove waste products.

The cardiovascular system kicks things off with the heart, which pumps oxygen- and protein-rich blood out through the arteries and into the body’s tissues and organs. The veins carry blood containing carbon dioxide and other waste products back to the heart.

About 90% of the blood gets sent back to the heart through the veins. But the remaining 10% is a fluid that leaks out into the body’s tissues through very tiny blood vessels called capillaries. This fluid — called lymph — contains protein, waste, cellular debris, bacteria, viruses, and excess fat that are all too big to get back into the veins.

The lymphatic system takes over from the cardiovascular system as lymph fluid moves throughout the body. Tiny vessels called lymphatic capillaries have small holes that allow lymph to pass through.

There is no heart-like pump for the lymphatic system. Instead, as you breathe and move your muscles, the lymph continuously gets pushed toward the heart from the outer parts of your body.

The way lymph moves through the body is similar to how blood that’s depleted of oxygen moves back toward your heart through the veins. First, the lymph moves out of the lymphatic capillaries and into larger lymphatic collector vessels. These vessels have muscular walls and one-way valves that keep the lymph moving in the right direction. Many of the lymphatic vessels sit just under the surface of your skin.

As the lymph makes its way back toward the heart, it has to pass through the lymph nodes — small, round masses that filter out bacteria, waste, and other toxins and also contain infection-fighting white blood cells. The lymph nodes play a key role in recognizing and destroying these substances, while also signaling the body to launch an immune response when needed.

You have clusters of lymph nodes in your groin, under your arms, and in your neck, and additional nodes located along other lymphatic pathways in the chest, abdomen, and pelvis. As the lymph moves out of different areas of the body, it slows down to get filtered by the regional lymph nodes. For example, lymph from the hand, arm, and under the arm, and from the chest and upper back areas, drains to the underarm (or axillary) lymph nodes to be filtered.

Eventually, the lymph travels to one of two large lymphatic ducts just below the neck, where it gets dumped into a large vein and back into the bloodstream. Once the debris and proteins have been filtered out, it’s safe for the fluid to join the bloodstream again. Just as blood is always circulating throughout your body, lymph is continuously being moved out of your tissues, through the lymphatic vessels and nodes, and back to the lymphatic ducts.

Lymphedema happens when the lymphatic system becomes damaged or overwhelmed and can’t clear lymph fast enough, so the fluid builds up and causes swelling.

Sometimes, an injury or infection can trigger lymphedema, especially if you have fewer lymph nodes as a result of breast cancer surgery.

When we injure ourselves or get an infection, the body’s tissues can get inflamed and make the lymphatic system work harder because blood flow and fluid both increase. If your lymphatic system can’t keep up, it can trigger lymphedema.

Other times, overusing a limb can trigger lymphedema. For example, when you use your arm more than you’re used to, your heart is pumping more blood through your arm than usual. More blood means more fluid in the tissues, which also means more lymph that can overwhelm the lymphatic system.