Potassium - RenalPotassiumHomeostasis I.DavidWeiner,M.D....

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Renal Potassium Homeostasis I. David Weiner, M.D. 374 6102 David.Weiner@medicine.ufl.edu www.RenalLectures.com Potassium is an essential mineral, present in all body fluids, both intracellular and extracellular, and for which abnormal concentrations result in substantial clinical disorders. Potassium deficiency leads to decreased insulin sensitivity, which can worsen diabetes mellitus, hypertension, decreased renal sodium excretion and increased susceptibility of the heart to the potentially fatal ventricular arrhythmias. Excessive extracellular potassium concentrations leads to muscle weakness and, eventually to lethal ventricular arrhythmias. Death by lethal injection uses an acute potassium overdose that causes the heart to “stop beating.” The majority of total body potassium is in the intracellular compartment. This is because of the Na + K + ATPase that is present in almost all cells and drives cellular K + uptake (Figure 1). The transmembrane K + gradient is the primary determinant of membrane voltage. Membrane voltage is important for both excitable (Figure 2) and non excitable cells, the body “works hard” to maintain the intracellular to extracellular K + gradient as constant as possible. As a result, when there is chronic K + deficiency the body shifts K + fromintracellular to extracellular compartments. This is important because potassium is commonly measured in the extracellular fluid compartment, not in the intracellular compartment. Consequently, potassium deficiency cannot be estimated from the change in extracellular potassium concentration multiplied by either plasma volume or even total body water. The relationship betweenhypokalemiaandtotalbody K + deficiencyisalmost exponential (Figure 3). ~ 3 Na
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Potassium - RenalPotassiumHomeostasis I.DavidWeiner,M.D....

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