The lymphatic system is one of two major systems responsible for moving fluid around your body. The other is the cardiovascular system. These two circulatory systems work together to make sure your body’s tissues can get what they need and get rid of what they don’t need.
If you’re like most people, you’re more familiar with how the heart and blood vessels work together as part of the cardiovascular system — but you may not know how the lymphatic system fits in. The heart 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, unused proteins, and other waste products back to the heart. About 90% of the blood gets sent back through the veins. But the other 10% of blood is a fluid component that leaks out into the body’s tissues through the very tiny blood vessels known as capillaries. This fluid contains protein, waste, cellular debris, bacteria, viruses, excess fat — things too big to get back into the veins.
At this point, the lymphatic system takes over. It too has tiny vessels known as lymphatic capillaries, but these capillaries have small holes in their walls that allow the fluid to pass through. This fluid is called lymph. 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 reaches of your body. (It’s very much like how blood 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 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, as well as more 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, as well as the chest and upper back areas, drains to the underarm (also known as 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. Now that 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.
It might help to think of your lymphatic system as a drainage network that has two important roles in your body: It maintains the balance of fluid by working right along with the cardiovascular system, and it plays a key part in the immune system by recognizing toxins and foreign substances — things that could harm the body if left unchecked.