reticuloendothelial system

reticuloendothelial system

or macrophage system or mononuclear phagocyte system

Part of the body's defenses, consisting of a class of cells widely distributed in the body. Reticuloendothelial cells filter out and destroy bacteria, viruses, and foreign substances and destroy worn-out or abnormal cells and tissues. Precursor cells in bone marrow develop into monocytes (see leukocyte), which are released into the bloodstream. Most enter body tissues, developing into much larger cells called macrophages, with different appearances in various locations. Some roam through the circulation and between cells and can coalesce into a single cell around a foreign object to engulf it. Reticuloendothelial cells also interact with lymphocytes in immune reactions. Cells in the spleen destroy old red blood cells and recycle their hemoglobin; uncontrolled, this process causes anemia. Tumours of the reticuloendothelial system can be localized or widespread throughout the body. Seealso lymphatic system.

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The reticuloendothelial system (RES), part of the immune system, consists of the phagocytic cells located in reticular connective tissue, primarily monocytes and macrophages. These cells accumulate in lymph nodes and the spleen. The Kupffer cells of the liver and tissue histiocytes are also part of the RES.

Mononuclear phagocytic system and lymphoreticular system are synonymous with RES.

The reticuloendothelial system is divided into primary and secondary lymphoid organs.

Primary lymphoid organs

Primary (or "central") lymphoid organs - the sites where the cells of the RES are produced. The cells of the RES are produced in the bone marrow.

The thymus is also included as it is the required site for T cell maturation.

Secondary lymphoid organs

Secondary (or "peripheral") lymphoid organs - the sites where the cells of the RES function. This includes the lymph nodes, tonsils, spleen, and "MALT" (mucosa-associated lymphoid tissue).

  • MALT is further divided into the "GALT" (gut-associated lymphoid tissue) and the "BALT" (bronchus-associated lymphoid tissue).
  • The Kupffer cells of the liver act as part of this system but are not organized into a tissue; rather, they are dispersed throughout the liver sinusoids.
  • The microglia of the Central Nervous System (CNS) can be considered a part of the reticuloendoethelial system. They are scavenger cells that proliferate in response to CNS injury.

Function

The secondary lymphoid structures function to survey all entering or circulating antigen and to mobilize an immune response against foreign antigen upon its discovery. The GALT and BALT are privy to a myriad of antigen entering the gastrointestinal and respiratory tracts, respectively. All extracellular fluid must filter through lymph nodes as it traverses the lymphatics on its way back to the systemic circulation. Antigen residing in the interstitium is thus swept to the lymph nodes for processing.

Finally, the spleen filters the blood in search of antigen. Upon the discovery of foreign antigen, all of these tissues react in a similar manner to amass an appropriate and multifaceted immune response.

Clinical significance

Lymphoma of the reticuloendothelial system is called reticuloendotheliosis.

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