Potassium Homeostasis

Overview (loncei 199&3S2.-13S)

• Renal: potassium excretion regulated at distal nephron (collecting tubule)

distal Na delivery & urine flow: Na absorption — lumen electronegative — K secretion aldosterone: increases Na absorption. K secretion

• Transcellular shifts: most common cause of acute change in serum potassium

Acid-base disturbance: K H' exchange across cell membranes Insulin — stimulates Na-K ATPase — hypokalemia

Catecholamines -♦ stimulate Na-K ATPase • hypokalemia; reversed by [i-blockers Digoxin blocks Na-K ATPase -* hyperkalemia

Massive necrosis (eg. tumor lysis, rhabdo. ischemic bowel) — release of intracellular K Hypo- or hyperkalemic periodic paralysis: rare disorders due to channel mutations

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