Effect of large changes in potassium intake on extracellular fluid potassium concentration under normal conditions (red line) and after the aldosterone feedback had been blocked (blue line). Note that after blockade of the aldosterone system, regulation of potassium concentration was greatly impaired. (Courtesy Dr. David B. Young.)
impairment of potassium regulation is observed in humans with poorly functioning aldosterone feedback systems, such as occurs in patients with either primary aldosteronism (too much aldosterone) or Addison's disease (too little aldosterone).
Increased Distal Tubular Flow Rate Stimulates Potassium Secretion. A rise in distal tubular flow rate, as occurs with volume expansion, high sodium intake, or diuretic drug treatment, stimulates potassium secretion. Conversely, a decrease in distal tubular flow rate, as caused by sodium depletion, reduces potassium secretion.
The mechanism for the effect of high-volume flow rate is as follows: When potassium is secreted into the tubular fluid, the luminal concentration of potassium increases, thereby reducing the driving force for potassium diffusion across the luminal membrane. With increased tubular flow rate, the secreted potassium is continuously flushed down the tubule, so that the rise in tubular potassium concentration becomes minimized. Therefore, net potassium secretion is stimulated by increased tubular flow rate.
The effect of increased tubular flow rate is especially important in helping to preserve normal potassium excretion during changes in sodium intake. For example, with a high sodium intake, there is decreased aldosterone secretion, which by itself would tend to decrease the rate of potassium secretion and, therefore, reduce urinary excretion of potassium. However, the high distal tubular flow rate that occurs with a high sodium intake tends to increase potassium secretion
Proximal |gFR 1 tubular Na+
reabsorption i Distal tubular I flow rate
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.