Lymph

Lymph is a clear, colorless or pale yellow fluid that circulates within the lymphatic system. It forms from interstitial fluid that bathes tissues and carries white blood cells, especially lymphocytes, as well as proteins, lipids, and cellular debris. Lymph travels through a network of blind-ended lymphatic capillaries, collecting vessels, and larger trunks, eventually returning to the bloodstream via the right lymphatic duct or the thoracic duct.

Key roles of lymph include maintaining fluid balance by returning excess interstitial fluid to the circulatory system and facilitating immune defense by conveying antigens and immune cells from tissues to lymph nodes. Lymph nodes filter lymph and are sites where lymphocytes become activated. Lymph also transports fats from the gut: fats absorbed by intestinal lacteals form chyle, a milky lymph that drains into the thoracic duct.

Anatomy and organization: lymphatic vessels and nodes are distributed throughout the body; lymphoid organs such as the spleen, thymus, tonsils, and mucosa-associated lymphoid tissue participate in immune responses. The spleen filters blood and stores lymphocytes; the thymus is where T cells mature; MALT tissues defend mucosal surfaces.

Clinical notes: disruption of lymph drainage can cause lymphedema; enlargement of lymph nodes (lymphadenopathy) can reflect infection or malignancy; lymphomas are cancers of lymphocytes. Chronic infection with filarial worms can cause elephantiasis, a severe form of lymphedema.