How the Lymphatic System Drains and Protects

The lymphatic system has two linked jobs. Its vessels return fluid and proteins from tissues to the bloodstream, while lymph nodes provide places where immune cells inspect material carried in lymph and organise responses. The spleen supports immune defence too, but it filters blood rather than lymph.

Fluid from tissues enters lymphatic vessels The fluid around tissue cells is called interstitial fluid . Some of it enters tiny lymphatic capillaries that begin within the tissues. These first lymphatic vessels are thin and blind ended, meaning closed at one end. Their structure allows fluid, proteins and some cells from the tissue space to enter. Once interstitial fluid is inside a lymphatic vessel, it is called lymph . Lymph moves back towards the bloodstream Small lymphatic vessels join into larger collecting vessels. These eventually feed into larger lymphatic ducts that return lymph to large veins near the base of the neck. There is no central pump equivalent to the heart. Larger collecting lymphatic vessels can contract, and nearby skeletal muscle movement and breathing also help move lymph. One way valves in collecting vessels help limit backward flow, so these different forces move lymph progressively towards the venous circulation. Lymph nodes are immune meeting points Lymph passes through lymph nodes positioned along the lymphatic network. These small structures contain organised groups of immune cells. Material carried in lymph can be captured and shown to immune cells. This helps the immune system recognise threats and organise a response. A node can enlarge when immune cells become activated and increase in number during an infection. Enlargement therefore reflects activity within the node, not simply fluid being trapped inside it. The spleen surveys blood rather than lymph The spleen sits high on the left side of the abdomen, under the ribs. It contains immune tissue, but it is connected to the bloodstream rather than sitting along the lymphatic drainage route. The spleen helps remove ageing or damaged red blood cells and supports immune responses to material carried in the blood. This is an important difference from lymph nodes, which receive lymph. Impaired lymphatic drainage can cause lymphoedema If lymphatic drainage is reduced, protein rich fluid can accumulate in the tissues. Persistent swelling caused by this problem is called lymphoedema . Lymphoedema can result from abnormalities in how the lymphatic system developed, or from later damage or blockage. Cancer treatment, infection, injury and surgery can all affect lymphatic drainage. Over time, persistent lymphoedema can change the affected tissues and increase the risk of skin infection.

Lymphatic vessels return tissue fluid to the bloodstream and carry lymph through immune rich lymph nodes. The spleen also supports immune defence, but it filters blood rather than lymph.