The document discusses major extra and intracellular electrolytes. It begins with an introduction to electrolytes, noting that they dissociate into cations and anions when dissolved in body fluids. It then describes the two main body fluid compartments: intracellular fluid contained within cells, and extracellular fluid outside of cells, consisting of plasma and interstitial fluid between cells. Finally, it discusses the importance of electrolyte balance for proper cell and organ function.