The function of lymphatic vessels is to aid in the return of interstitial fluid to intra-vascular volume. They assist with transport of lipids from the gastro- intestinal tract to the blood and also aid in filtering out pathogenic organism. The lymphatic vessels are similar to the capillaries and are located in large numbers in organ systems that frequently have direct contact with the external environment. They have nodular systems that act as filters by phagocytic action within them. The large lymphatic vessel return lymph to the circulating blood volume via thoracic duct into the subclavian veins.