This is a clear or pale fluid that flows around the body’s tissues and contains white blood cells that fight infection. Lymph starts out as plasma, the liquid part of blood. As blood flows through the body, some of this plasma leaks into the spaces between cells. Here, it picks up waste products, such as pieces of cells that have died. It also picks up viruses and bacteria. Then the liquid, now called “lymph,” enters microscopic lymph capillaries.
Lymph flows from these capillaries to larger channels, called lymph vessels. These vessels carry lymph back to the bloodstream. But first, lymph enters bean-shaped nubs of tissue called lymph nodes. Lymph nodes remove waste products and other materials from lymph. Lymph nodes also contain white blood cells called lymphocytes. These cells prepare the body to attack invaders, such as viruses and bacteria. If they detect these invaders, they destroy them or tell the body to make more infection-fighting cells.
The lymph vessels and nodes are part of the body’s lymphatic (Lim-FAAH-tic) system. This system also includes organs such as the spleen and tonsils, which make lymphocytes. In addition to helping fight disease, the lymphatic system also helps balance the body’s fluids.