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.
An oncogene is a gene that has the potential to cause cancer cancer. Oncogenes were first described as retrovirus-encoded genes that produced tumors in birds and rodents. These genes were then shown to be dominant mutated forms of host genes. (proto-oncogenes) that had been picked up by the retroviruses. Generally they are in the form of a proto-oncogene in the normal cell. Most oncogenes require an additional step, such as mutations in another gene, or environmental factors like non-ionizing or ionizing radiation, or more likely a viral infection, to cause cancer. Many cancer drugs target the proteins encoded by oncogenes.