Lymphatic system

In mammals including humans, the lymphatic vessels (or lymphatics) are a network of thin tubes that branch, like blood vessels, into tissues throughout the body. Lymphatic vessels carry lymph, a colorless, watery fluid originating from interstitial fluid (fluid in the tissues). The lymphatic system transports infection-fighting cells called lymphocytes, is involved in the removal of foreign matter and cell debris by phagocytes and is part of the body's immune system. It also transports fats from the small intestine to the blood.

Secondary lymphoid organs

The spleen, lymph nodes, and accessory lymphoid tissue (including the tonsils and appendix) are the secondary lymphoid organs. These organs contain a scaffolding that support circulating B- and T-lymphocytes and other immune cells like macrophages and dendritic cells. When microorganisms invade the body or the body encounters other antigens (such as pollen), the antigens are transported from the tissue to the lymph. The lymph is carried in the lymph vessels to regional lymph nodes. In the lymph nodes, the macrophages and dendritic cells phagocytose the antigens, process them, and present the antigens to lymphocytes, which can then start producing antibodies or serve as memory cells to recognize the antigens again in the future.

Related Topics:
Spleen - Lymph nodes - Tonsil - Appendix - Macrophage - Dendritic cell - Phagocytose - Antibodies

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The spleen contains lymphocytes that filter the blood stream rather than the lymphatics. Thus, the spleen has importance in fighting infections that have invaded the blood.

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Accessory lymphoid tissues act as barriers along points of entry for infections, such as the lung, the reproductive system, and the gut. (See separate section below).

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