Anatomy
The lymphatic system is comprised of vessels, nodes, and other lymphoid tissues, such as the spleen.
Vessels of the lymphatic system are found throughout most of the body. Lymphatic capillaries permeate the tissues and merge into larger vessels. Those larger vessels follow veins and assist in returning lymphatic fluid to circulation.
Lymph nodes are situated along lymphatic vessels, and are concentrated in various regions of the body. Those regions include neck, axilliary (armpits), abdomen, and groin. They act as filters and produce cells that are part of the immune response.
The fluid passing through the lymphatic system is called lymph. It is composed, in part, of large proteins, white blood cells, waste products, and water.
Function
A primary role of the lymphatic system is to remove excess fluid and particles from the interstitial tissue spaces. It is estimated that 10 percent of lymphatic fluid including large proteins is not directly returned to circulation by the venous system and must instead be removed by the lymphatic system. As lymph returns to the venous system, it must pass through the lymph nodes, where bacteria, viruses, and other particles are removed.
The lymphatic system lacks a central, heart-like propulsion mechanism. Instead, lymph flow arises from peripheral mechanisms including contraction of the muscles of the body. Contraction of muscles that surround the larger lymphatic vessels prevent backflow.