Mechanism of distal K secretion Figure 512

(a) At the basolateral membrane, K+ is actively transported into the cell by the Na+-K+ pump. As in all cells, this mechanism maintains a high intracellular K+ concentration.

(b) At the luminal membrane, K+ is passively secreted into the lumen through K+ channels. The magnitude of this passive secretion is determined by the chemical and electrical driving forces on K+ across the luminal membrane.

- Maneuvers that increase the intracellular K+ concentration or decrease the luminal K+ concentration will increase K+ secretion by increasing the driving force.

- Maneuvers that decrease the intracellular K+ concentration will decrease K+ secretion by decreasing the driving force.

(2) Factors that change distal K+ secretion (see Figure 5-12 and Table 5-5)

- Distal K+ secretion by the principal cells is increased when the electrochemical driving force for K+ across the luminal membrane is increased. Secretion is decreased when the electrochemical driving force is decreased, (a) Dietary K+

- A diet high in K+ increases K+ secretion, and a diet low in K+ decreases K+ secretion.

Table 5-5. Changes in Distal K+ Secretion

Causes of Increased Distal K+ Secretion

High-K+ diet Hyperaldosteronism Alkalosis Thiazide diuretics Loop diuretics Luminal anions

Causes of Decreased Distal K' Secretion

Low-K+ diet

Hypoaldosteronism

Acidosis

K+-sparing diuretics

Lumen

Principal cell of distal tubule

Blood

(Aldosterone) Na+

(Acid-base)

Figure 5-12. Mechanism of K* secretion in the principal cell of the distal tubule.

- On a high-K+ diet, intracellular K+ increases so that the driving force for K+ secretion also increases.

- On a low-K+ diet, intracellular K+ decreases so that the driving force for K+ secretion decreases. Also, the a-intercalated cells are stimulated to reabsorb K+ by the H+,K+-ATPase.

Was this article helpful?

0 0
Weight Loss All Star

Weight Loss All Star

Are you looking to lose weight or even just tone up? What is stopping you from having the body you want and help you feel great at the same time? I created Weight Loss All-Star for all those wanting to lose weight, and keep the weight off. I know how hard it is to do diets and stick with them, and get the motivation to get up and exercise.

Get My Free Ebook


Post a comment