Lymphatic System

The lymphatic system is the body's network of organs, ducts, and tissues that filter harmful substances out of the fluid that surrounds body tissues. Lymphatic organs include the bone marrow, thymus, spleen, appendix, tonsils, adenoids, lymph nodes, and Peyer's patches (in the small intestine). The thymus and bone marrow are called primary lymphatic organs, because lymphocytes are produced in them. The other lymphatic organs are called secondary lymphatic organs.

Lymphocytes are a type of white blood cell (wbc), which is highly concentrated in lymphatic fluid. This clear fluid, also called lymph, travels through the lymphatic vessels, which connect the lymphatic organs. The terminal lymphatic vessels feed into the thoracic duct that returns body fluids to the heart prior to blood reoxygenation. The reincorporated fluid originates in the bloodstream, bathes organs and tissues, and is returned to the bloodstream after passing through lymphatic filters that function as part of the body's defense system against infection and cancer.

Lymph nodes, primarily clustered in the neck, armpits, and pelvic area, are the system's battle stations against infection. Lymph nodes are connected to one another by lymphatic vessels. It is in the nodes and other secondary organs where wbcs engulf and destroy debris to prevent them from reentering the bloodstream. Of the other two major secondary lymphatic organs, the spleen removes dead red blood cells (rbcs), and Peyer's patches remove intestinal antigens (foreign or harmful substances in the body).