SIGNIFICANCE
OF POTASSIUM
Potassium is the major intracellular electrolyte; in fact, 98% of the
body’s potassium is inside the cells. The remaining 2% is in the ECF, and it is
this 2% that is important in neuromuscular func-tion. Potassium influences both
skeletal and cardiac muscle activ-ity. For example, alterations in its
concentration change myocardial irritability and rhythm. Under the influence of
the sodium– potassium pump and based on the body’s needs, potassium is
con-stantly moving in and out of cells. The normal serum potassium
concentration ranges from 3.5 to 5.5 mEq/L (3.5–5.5 mmol/L), and even minor
variations are significant. Potassium imbalances are commonly associated with
various diseases, injuries, medica-tions (diuretics, laxatives, antibiotics),
and special treatments, such as parenteral nutrition and chemotherapy (Cohn et
al., 2000).
To maintain potassium balance, the renal system must func-tion because
80% of the potassium is excreted daily from the body by way of the kidneys; the
other 20% is lost through the bowel and in sweat. The kidneys are the primary
regulators of potassium balance and accomplish this by adjusting the amount of
potassium that is excreted in the urine. As serum potassium levels increase, so
does the potassium level in the renal tubular cell. A concentration gradient
occurs, favoring the movement of potassium into the renal tubule with the loss
of potassium in the urine. Aldosterone also increases the excretion of
potassium by the kidney. Because the kidneys do not conserve potassium as well
as they conserve sodium, potassium may still be lost in urine in the presence
of a potassium deficit.
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