Chapter 5: Potassium

Potassium overview explores the vital physiological regulation and clinical management of potassium, the body's primary intracellular cation, which is crucial for maintaining electrical gradients and cardiac stability. It delves into the complex mechanisms of potassium homeostasis, examining how the kidneys manage daily intake through glomerular filtration and regulated distal tubular secretion—a process heavily influenced by aldosterone levels and the availability of sodium for exchange. The narrative highlights the critical role of the sodium-potassium ATPase pump in maintaining the massive intracellular reservoir and discusses how transcellular shifts, driven by insulin activity, catecholamine release, and pH imbalances, can dramatically alter plasma concentrations. Students will find detailed breakdowns of hypokalaemia, including renal causes like mineralocorticoid excess and non-renal triggers such as gastrointestinal loss or malnutrition, alongside its characteristic electrocardiogram manifestations like flattened T waves and prominent U waves. The text equally prioritizes the life-threatening nature of hyperkalaemia, a condition frequently stemming from acute kidney injury, chronic kidney disease, or the pharmacological effects of ACE inhibitors and potassium-sparing diuretics. By integrating diagnostic indices such as the transtubular potassium gradient (TTKG) and plasma bicarbonate levels, the chapter provides a systematic framework for differentiating electrolyte disorders and implementing urgent interventions, including the administration of calcium gluconate for cardiac protection and insulin-glucose infusions to facilitate rapid cellular uptake of excess ions.