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.
The term is derived from bacteria and the Greek: ÏÎ±Î³Îµá¿Î½ (phagein), to devour. Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes, and as many as hundreds of genes.Phages replicate within the bacterium following the injection of their genome into its cytoplasm.acteriophages may have a lytic cycle or a lysogenic cycle, and a few viruses are capable of carrying out both. With lytic phages such as the T4 phage, bacterial cells are broken open (lysed) and destroyed after immediate replication of the virion.