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lymphatic system

A component of the circulatory system comprising the lymphatics and the lymphoid tissues. SEE: illus.; immune response; immune system; lymph.













 LYMPHATICS: The lymphatics begin with the lymphatic capillaries, permeable endothelial vessels one-cell thick, which absorb interstitial tissue fluid, particles, microbes, debris, and, from the small intestines, fat. Lymphatic capillaries empty into larger lymph vessels that eventually empty their contents (lymph) into the venous circulation through lymphatic ducts.

 LYMPHOID TISSUES: Lymph nodes are interposed between lymph vessels at some of the junctions between vessels. As it percolates through a lymph node, lymph is modified: debris is filtered out, lymphocytes are activated, and antibodies and lymphocytes are added to the fluid. Other lymphoid tissues have similar functions: The spleen filters the circulating blood, to which it adds antibodies and lymphocytes. Tonsils, Peyer patches, and other unencapsulated lymphoid tissues line epithelia that are in contact with the outside environment; unencapsulated lymphoid tissues activate lymphocytes and manufacture antibodies against foreign antigens. Lymphoid tissues in the bone marrow are proliferation and activation centers for lymphocytes, and the thymus is a proliferation and maturation center for T lymphocytes, esp. during the neonatal and early postnatal years.


(lim″fi-dē′mă) [lymph + edema] An abnormal accumulation of tissue fluid in the interstitial spaces due to the removal of lymph nodes or to the blockage or destruction of lymphatics. Stagnant flow of tissue fluid through body structures may make them prone to infections that are difficult to treat; as a result lymphedematous limbs should be protected from cuts, scratches, burns, and blood drawing. SEE: illus.





 SEE: lymphatic blockade; elephantiasis; lymphedema pump.

 CAUSES: Common causes of lymphedema include neoplastic obstruction of lymphatic flow (as in the axilla, in metastatic breast cancer); postoperative interference with lymphatic flow (after axillary dissection); infectious blockade of lymphatics (in filariasis); radiation damage to lymphatics (after treatment of pelvic, breast, or lung cancers). All of these are secondary (acquired) lymphedemas. Rarely, lymphedema also may occur congenitally (Milroy disease), or develop at the onset of puberty or during adulthood from an unknown cause that may be related to vascular anomalies (primary lymphedema). In the U.S. and other developed countries, the leading cause of secondary lymphedema is surgical or radiation therapy for cancer, esp. if accompanied by lymph node dissection.

 SYMPTOMS AND SIGNS: Symptoms of lymphedema include a feeling of ...

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