potassium (K) /pətas″ē·əm/ [D, potasschen, potash] , an alkali metal element, the seventh most abundant element in the earth’s crust. Its atomic number is 19; its atomic mass is 39.10. Potassium salts are necessary to the life of all plants and animals. Potassium in the body constitutes the predominant intracellular cation, helping to regulate neuromuscular excitability and muscle contraction. Sources of potassium in the diet are whole grains, meat, legumes, fruit, and vegetables. The average adequate daily intake for most adults is 2 to 4 g. Normal adult levels of blood potassium are 3.5 to 5 mEq/L or 3.5 to 5 mmol/L (SI units). Potassium is important in glycogen formation, protein synthesis, and correction of imbalances of acid-base metabolism, especially in association with the action of sodium and hydrogen ions. Potassium salts are very important as therapeutic agents but are extremely dangerous if used improperly. The kidneys play an important role in controlling the secretion and absorption. Aldosterone stimulates sodium reabsorption and potassium secretion by the kidneys. The major extrarenal adaptation to this process involves the absorption of potassium by the body tissues, especially the tissues of the muscles and the liver. Potassium is most commonly depleted in the body by an increased rate of excretion by the kidneys or the GI tract. Increased renal excretion may be caused by diuretic therapy, large doses of anionic drugs, or renal disorders. Increased GI excretion of potassium may occur with the loss of GI fluid through vomiting, diarrhea, surgical drainage, or chronic use of laxatives. Potassium loss through the skin is rare but can result from perspiring during excessive exercise in a hot environment.
