Potassium is freely filtered in the glomerulus. Two-thirds of the potassium is reabsorbed along the proximal tubule. The concentration of potassium in the proximal tubule is approximately the same as that in plasma. In the descending branch of Henle a small amount of potassium is secreted into the luminal fluid and is reabsorbed by the ascending branch of Henle. The potassium concentration in the distal convoluted tubule is now lower than the concentration in the plasma. The connecting tubule and the cortical connecting tubule actively secrete potassium into the lumen. Potassium is then reabsorbed in the medullary segment while the excess is excreted in the urine.[5 and 6]The regulation of potassium occurs mainly in the distal tubule and the cortical collecting tubule. The balance of potassium in the body will determine whether the tubules reabsorb or secrete potassium. If the body has a deficiency of potassium, reabsorption will occur, if the body has an excess of potassium, secretion will occur. [5 and 6] Mechanism of potassium secretion: [5] In cells of the distal final tubule and cortical collecting tubule, the basolateral membrane contains the sodium/potassium ATPase pump and a potassium channel. The apical membrane contains both sodium and potassium channels.[5]The pump is sensitive to the concentration of potassium in the blood. When extracellular potassium increases, the pump increases in activity and more potassium is absorbed by the cell, when the plasma concentration is low the opposite occurs. [5]The pump exchanges three molecules of sodium with two molecules of potassium. Thus, an electrical gradient is formed across the basolateral membrane of the cell due to the charge imbalance generated. The inside of the cell is negative by about 80 mV compared to the outside... half the paper... potassium decreases and intracellular concentration increases. The permeability of the apical membrane increases and potassium passes easily through potassium channels. Potassium excretion increases and plasma potassium concentration decreases. [5]Changes in plasma concentration due to acid-base disturbance are generally minimal. [5]Conclusion: [5]Extra-renal factors (insulin, epinephrine, aldosterone) and renal factors maintain a normal plasma potassium concentration in the body. Extra-renal mechanisms are responsible for the movement of potassium into the intracellular compartment. Renal mechanisms are responsible for the chronic maintenance of the body's potassium content. When these mechanisms are functioning properly, high potassium intake has a minor and insignificant effect on plasma potassium concentration. [5&6]