Physiology of Potassium Regulation
On the basis of the present analysis, one may concluded that aldosterone is a major component of the system that regulates potassium over long time periods. The hormone’s participation in the control system is regulated by the multiplicative interaction of the two stimuli of aldosterone secretion, angiotensin II and plasma potassium concentration. The most prominent regulator of potassium excretion is the direct effect of changes in extracellular potassium concentration on secretion of the ion into the distal nephron. This mechanism is approximately three times as powerful as the aldosterone effect in increasing potassium excretion in response to increases in the rate of potassium intake. Aldosterone participates in control of the distribution of potassium between the intra-and extracellular spaces, a greater proportion of total body potassium being within the cells at higher levels of aldosterone. The shift in distribution can be large so that plasma potassium concentration may fall by 1.0 mmol/L or more with only small change in potassium excretion in response to a several fold increase in aldosterone concentration. Aldosterone’s most prominent function in potassium regulation is in preventing changes in potassium excretion during changes in sodium excretion. Increases in flow through the potassium-secreting portion of the distal nephron strongly augment potassium secretion. However, as distal flow increases, for example following an increase in sodium intake, aldosterone secretion decreases as a result of a reduction in renin release and angiotensin II concentration; the reduced aldosterone concentration offsets the kaliuretic influence of the increase in flow rate, so that in general, no change in potassium balance occurs. Aldosterone is not the most powerful component of the systems regulating potassium and excretion, but the aldosterone component is the only mechanism that enables the system to simultaneously maintain balance of both potassium and sodium over wide combined ranges of intakes of the two ions
KeywordsPermeability Angiotensin Luminal Norepinephrine Peri
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