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Tham khảo tài liệu 'chapter 046. sodium and water (part 11)', y tế - sức khoẻ, y học thường thức phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 046. Sodium and Water Part 11 Potassium Introduction Potassium Balance Potassium is the major intracellular cation. The normal plasma K concentration is 3.5-5.0 mmol L whereas that inside cells is about 150 mmol L. Therefore the amount of K in the ECF 30-70 mmol constitutes 2 of the total body K content 2500-4500 mmol . The ratio of ICF to ECF K concentration normally 38 1 is the principal result of the resting membrane potential and is crucial for normal neuromuscular function. The basolateral Na K -ATPase pump actively transports K in and Na out of the cell in a 2 3 ratio and the passive outward diffusion of K is quantitatively the most important factor that generates the resting membrane potential. The activity of the electrogenic Na K -ATPase pump may be stimulated as a result of an increased intracellular Na concentration and inhibited in the setting of digoxin toxicity or chronic illness such as heart failure or renal failure. The K intake of individuals on an average western diet is 40-120 mmol d or approximately 1 mmol kg per day 90 of which is absorbed by the gastrointestinal tract. Maintenance of the steady state necessitates matching K ingestion with excretion. Initially extrarenal adaptive mechanisms followed later by urinary excretion prevent a doubling of the plasma K concentration that would occur if the dietary K load remained in the ECF compartment. Immediately following a meal most of the absorbed K enters cells as a result of the initial elevation in the plasma K concentration and facilitated by insulin release and basal catecholamine levels. Eventually however the excess K is excreted in the urine see below . The regulation of gastrointestinal K handling is not well understood. The amount of K lost in the stool can increase from 10 to 50 or 60 of dietary intake in chronic renal insufficiency. In addition colonic secretion of K is stimulated in patients with large volumes of diarrhea resulting in potentially severe K depletion. Potassium
