Lymphatic System Overview
The lymphatic system is part of the circulatory system and a vital part of the immune system, comprising a network of lymphatic vessels that carry a clear fluid called lymph directionally towards the heart. Unlike the cardiovascular system, the lymphatic system is not a closed system. The system helps to equalize fluid distribution. The interstitial fluid pressure is greater than lymphatic pressure which causes lymph vessel flaps open to open. This allows interstitial fluid to enter lymphatic capillaries where lymphatic circulation merges with veins and returns the fluid to blood. When interstitial fluid pressure is less than lymphatic pressure, the lymph vessel flaps close to prevent lymph from leaking back out. Lymph is the clear fluid that leaks out of the capillaries. It is composed mainly of water, plasma protein, chemicals and white blood cells. Lymph is generated by the diffusion of the relevant materials from capillaries by differential pressure. The lymphatic system transports proteins and large glycerides and fats get absorbed into the lacteals in the small intestine. Lacteal refers to the lymphatic capillary in the small intestine. Plasma proteins as well as cells that leak into the interstitial fluids get returned to the blood via the lymphatic system. The lymphatic system is also the site of the production of lymphocytes involved in immune reactions. Lymphocytes are produced in the bone marrow from blood stem cells but lymphoid tissues provide a place where lymphocytes can reside, proliferate, and differentiate. Lymphoid tissue is found in the lymph nodes, thymus, and scattered throughout various organs such as the spleen. Lymph tissue contains many lymphocytes that filters lymph. The thymus is the place where T cells mature. The lymphatic system also transports substances similar to blood. When pathogens or foreign antigens get inside a lymph node, lymphocytes that reside there get activated. Upon activation, lymphocytes start releasing chemicals that stimulate an immune response. This involves proliferation, antibody production and release of cytokines.