What is the most important electrolyte for the maintenance of osmotic pressure and volume in the extracellular fluid compartment? The most abundant positive ion or cation in the extracellular fluid  is sodium (Na+). Chloride (Cl-) is the most abundant negative ion  or anion.
Medical Definition of MACROPHAGE. : a phagocytic tissue cell of the immune system that may be fixed or freely motile, is derived from a monocyte, functions in the destruction of foreign antigens (as bacteria and viruses), and serves as an antigen-presenting cellâsee histiocyte, mononuclear phagocyte system. a phagocytic tissue cell of the immune system that may be fixed or freely motile, is derived from a monocyte, functions in the destruction of foreign antigens (as bacteria and viruses), and serves as an antigen-presenting cell â compare histiocyte. â macÂ·roÂ·phagÂ·ic \Ëma-krÉ-Ëfa-jik\ adjective.
Macrophages are a type of white blood cell which eat foreign material in the body. These cells are involved in the primary or innate immune response to a number of immune invaders, and they also make up an important part of the body's acquired immune system.acrophages help clean up bacteria and viruses in the body. Macrophages can be co-opted by HIV cells and aid the spread of the virus. A monocyte is the first stage of life for a macrophage. Macrophages are a type of white blood cell that eats foreign material in the body.