Sodium Balance

Abstract

²⁴Na injected in a human subject dilutes in 24 hours into 2500–3000 mmol Na, about 45 mmol/kg body weight (Edelman and Liebman, 1959). This is called exchangeable Na and is the mass of Na primarily concerned in Na balance. In addition there is about 1000 mmol Na which is part of the crystalline structure of bone and which can be altered only slowly and probably takes no part in normal Na balance as discussed in this chapter or the acute experiments of Chapter 8. The distribution of exchangeable Na is shown in Table 26. Na is the cation of extracellular fluids where its concentration is 140–150 mmol/kg water as in plasma. Inside cells the concentration of Na is only a few mmol/kg water, with K the intracellular cation.