Potassium homeostasis.

Potassium balance is regulated by appropriate changes in potassium excretion in the distal portion of the nephron. By contrast, potassium intake, absorption and proximal renal reabsorption do not show regulatory variation. Extracellular potassium concentration, which is a critical factor in membrane polarization, may at times vary in a direction opposite to total body content, because of altered distribution across cell membranes. Alterations in acid-base status frequently disturb homeostasis by altering potassium movement into cells, while insulin has an important regulatory effect on distribution. In general, the multiple renal and extra-renal mechanisms which prevent potassium overload are highly developed, while conservation is relatively ineffective. Consequently, depletion occurs more easily than spontaneous potassium overload. Homeostasis can be disturbed by renal impairment, excessive tissue breakdown, disturbances of acid-base balance, abnormal routes of loss, mineralocorticoid abnormalities and aberrations of sodium balance.