sodium (Na) /sō″dē·əm/ [soda + L, ium] , a soft grayish metal of the alkaline metals group. Its atomic number is 11; its atomic mass is 22.99. Sodium is one of the most important elements in the body. Sodium ions are involved in acid-base balance, water balance, transmission of nerve impulses, and contraction of muscles. The recommended daily intake of sodium is 250 to 750 mg for infants 6 months to 1 year of age, 900 to 2700 mg for children 11 years of age or older, and 1100 to 3300 mg for adults. Sodium is an important component of more than 8 L of secretions produced by the body every day. These secretions include saliva, gastric and intestinal secretions, bile, and pancreatic fluid. The total daily secretion of sodium into these alimentary tract fluids averages between 1200 and 1400 mEq. A 154-pound adult has a total body pool of 2800 to 3000 mEq. It is also linked to chlorine, which is the most important extracellular anion in the body. Sodium is the chief electrolyte in interstitial fluid, and its interaction with potassium as the main intracellular electrolyte is critical to survival. A decrease in the sodium concentration of the interstitial fluid immediately decreases osmotic pressure, making it hypotonic to intracellular fluid osmotic pressure. The kidney is the chief regulator of sodium levels in body fluids and will excrete sodium-free urine when the body needs to conserve sodium. In high temperatures, such as those associated with fever, the body loses sodium through sweat, and sodium reserves are further diluted with additional water drunk by the affected individual. To prevent serious complications, depleted sodium must be replaced. Sodium salts, such as sodium bicarbonate, are widely used in medications. Sodium bicarbonate has an immediate and rapid antacid action on the stomach, but any excess rapidly enters the intestine so that the substance has a shorter action than that of other antacids. Sodium bicarbonate, which is very effective in rendering the urine alkaline, is an ingredient in many solutions used as douches, mouthwashes, and enemas. Sodium is also important in the transport of sodium and potassium ions through the cytoplasmic membrane.
