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Chapter: Medical Surgical Nursing: Assessment and Management of Patients With Hematologic Disorders

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Reticuloendothelial System(RES)

The RES is composed of special tissue macrophages, which are derived from monocytes.

RETICULOENDOTHELIAL SYSTEM (RES)

 

The RES is composed of special tissue macrophages, which are derived from monocytes. When released from the marrow, monocytes spend a short time in the circulation (about 24 hours) and then enter the body tissues. Within the tissues, the mono-cytes continue to differentiate into cells called macrophages, which can survive for months. Macrophages have a variety of im-portant functions. They defend the body against foreign invaders (ie, bacteria and other pathogens) via phagocytosis. They remove old or damaged cells from the circulation. They stimulate the in-flammatory process and present antigen to the immune system. Macrophages give rise to tissue histiocytes, in-cluding Kupffer cells of the liver, peritoneal macrophages, alveo-lar macrophages, and other components of the RES. Thus, the RES is a component of many other organs within the body, par-ticularly the spleen, lymph nodes, lung, and liver.

 

The spleen is the site of activity for most macrophages. Most of the spleen (75%) is made of red pulp; here the blood enters the ve-nous sinuses through capillaries that are surrounded by macro-phages. Within the red pulp are tiny aggregates of white pulp, consisting of B and T lymphocytes. The spleen sequesters newly re-leased reticulocytes from the marrow, removing nuclear fragments and other materials (eg, denatured hemoglobin, iron) before the now fully mature RBC returns to the circulation. Although a minority of RBCs (less than 5%) is pooled in the spleen, a signifi-cant proportion of platelets (20%–40%) is pooled here. If the spleen is enlarged, a greater proportion of RBCs and platelets can be sequestered. The spleen is a major source of hematopoiesis in fetal life. It can resume hematopoiesis later in adulthood if neces-sary (eg, in bone marrow fibrosis). The spleen has important im-munologic functions as well. It forms a substance that promotes the phagocytosis of neutrophils; it also forms the antibody IgM after exposure to antigen.

 

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