What Is the Reticuloendothelial System?
The reticuloendothelial system (RES) is an essential component of the immune system, comprised of phagocytic cells located in different organs of the human body. Phagocytic cells capable of engulfing substances, such as bacteria and viruses, rendering them incapable of causing harm to the body. They also ingest abnormal cells and old cells, thus clearing the body of their harmful presence.
Phagocytic cells are derived from the bone marrow stem cells and become monocytes, which circulate in the blood. Most of these monocytes migrate to different tissues inside the body. When they are no longer in the blood circulation, they are called macrophages. Macrophages are generally larger than monocytes and are mostly located in tissues such as the lymph nodes, liver, spleen, brain, and subcutaneous tissues.
The appearance of macrophages differ depending on the organs in which they reside, where they are also given specific names. They are called Kupffer cells when they are found in the liver. In the brain they are known as microglia. When found in the lymph nodes, bone marrow, and spleen, they are named reticular cells. Tissue histiocytes or fixed macrophages are the names used when they are located in the subcutaneous tissues, and while in the lungs they are known as alveolar cells.
Cells of the reticuloendothelial system often remain fixed to these organs, and they function as the first line of protection and defense of the body. They mostly filter and destroy objects which are foreign to the body, such as bacteria, viruses, and bits of sutures or threads used during surgery. Some macrophages are mobile, and they can group together to become one big phagocytic cell in order to ingest larger foreign particles.
The functions of the reticuloendothelial system are not only limited to the ingestion of these foreign substances. The reticuloendothelial system is also important in presenting these substances to other cells of the immune system, such as the lymphocytes. Lymphocytes in turn secrete specific antibodies which can directly destroy specific bacteria and viruses. They are cells capable of remembering specific foreign substances, and render protection by attacking these specific bacteria and viruses every time they enter the body.
One other vital function of the reticuloendothelial system is carried out by the spleen. The spleen is a specialized organ capable of removing old and deformed cells from blood circulation. It is also capable of breaking down worn-out or old red blood cells (RBC) and keeping the hemoglobin part of the RBC to be used again by the body.
Written by Dulce Corazon
