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1 Sodium plays a large role in fluid balance, with different variations of sodium determining the shift of water by osmosis from one area of the body to another.  Along with chloride and bicarbonate, sodium is important for the proper regulation of the acid-base balance of the body.
sodium. a chemical element, atomic number 11, atomic weight 22.990, symbol Na. (See Appendix 6.) Sodium is the major cation of the extracellular fluid, constituting 90 to 95 per cent of all cations in the blood plasma and interstitial fluid; it thus determines the osmolality of the extracellular fluid.ts atomic number is 11, and its atomic weight is 22.9898. Sodium is one of the most important elements in the body. Sodium ions are involved in acid-base balance, water balance, the transmission of nerve impulses, and the contraction of muscle.