The lymphatic system is a network of specialized vessels (lymph vessels) throughout the body whose purpose is to collect excess lymph fluid with proteins, lipids, and waste products from the tissues. This fluid is then carried to the lymph nodes, which filter waste products and contain infection-fighting cells called lymphocytes. The excess fluid in the lymph vessels is eventually returned to the bloodstream. When the lymph vessels are blocked or unable to carry lymph fluid away from the tissues, localized swelling (lymphedema) is the result.