3. Physiology
        3.12. Renal
3.12.8. Renal regulation of potassium

Renal regulation of potassium

K+ is freely filtered

 

Contribution by segments

In cortical collecting duct

In medullary collecting duct

NB:

 

Mechanisms of K+ reabsorption

Proximal tubules

Paracellular diffusion (secondary to water reabsorption)

Thick ascending limb

Mainly by Na-K-2Cl symporter

Partially by paracellular diffusion

Cortical collecting duct

Principle cells

Secrete K+
* Active transport of K+ from interstitium into cell across basolateral membrane
* Then passive diffusion out of the cell (back into interstitium or into lumen by luminal K+ channels or K-Cl symporter)
* Diffusion into lumen predominates due to negative charged lumen and greater number of luminal K+ channel

Type A Intercalated cells

Reabsorb K+ by H-K antiporter
* Thus H+ is secreted in exchange for K+

 

Factors affecting K+ secretion

  1. [K+] in blood perfusing kidney
  2. Plasma level of aldosterone
  3. Delivery of Na+ to distal nephrone
  4. Flow rate in collecting duct

Aldosterone

Aldosterone stimulate secretion by

When aldosterone decreases due to increased [Na+]

--> Reduced aldosterone reduces K+ secretion, which is offset by increased flow rate to the cortical collecting duct

Thus,

NB:

Delivery of Na+

Flow rate in collecting duct

Remember K+ secretion is essentially a passive process

Thus, when flow rate is high

--> Less opportunity for [K+] in tubule to raise up to significant level

--> Increased [K+] secretion

Effects of diuretics

Reabsorption is reduced

However, increased K+ loss is due to increased excretion by cortical collecting ducts

Because:

 

 

 

 

 



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