5. Regulation of K+ Balance Flashcards
How does strenuous exercise affect potassium balance?
Strenuous exercise enhances potassium efflux by increasing the presence of alpha-catecholamines.
What is the function of aldosterone in potassium balance?
Renal: Increased potassium excretion by the kidney
Extrarenal: Increased potassium excretion through saliva and intestinal fluids.
Overall, what do alpha-intercalated cells reabsorb/secrete?
Reabsorb: potassium: bicarbonate
Secrete: hydrogen ion and chloride
What cell type reabsorbs potassium in the distal tubule?
Alpha-intercalated cells
What is the function of alpha-catecholamines on potassium balance?
Alpha catecholamines decrease cell uptake of potassium by decreasing the activity of Na/K ATPase – by decreasing available cAMP.
What are the two (listed) factors which stimulate potassium reabsorption?
Potassium deficiency (hypokalemia, or low potassium diet)
Potassium loss through severe diarrhea.
What is the function of beta-catecholamines on potassium balance?
Beta catecholamines enhanced cell uptake of potassium by increasing the activity of the Na/K ATPase – by increasing available cAMP
Overall, what do beta-intercalated cells reabsorb/secrete?
Reabsorb: hydrogen ion, chloride
Secrete: potassium, bicarbonate
Overall, what do principal cells reabsorb/secrete?
Reabsorb: sodium, H2O
Secrete: potassium
What is the basic mechanism for the effect of alkalosis on plasma potassium levels?
Alkalosis (increased pH) causes an increased activity in the Na/K ATPase of the distal tubule.
This results in a buildup of potassium inside the cells of the tubular lumen, which provides the concentration gradient for potassium to be secreted.
This causes hypokalemia.
What are the six listed factors that stimulate potassium secretion?
Aldosterone.
Concentration of potassium in the extracellular fluid.
Increased tubular flow rates.
Stimulation of the Na/K ATPase.
Reduced back leakage of potassium (ICF through basolateral membrane).
Increase in synthesis of potassium channels inserted into the luminal membrane.
(All six increase potassium secretion)
How do we ensure sodium makes it to the distal tubule to be available for significant potassium secretion if necessary?
Potassium is secreted by the inner and outer medullary collecting duct into the interstitial fluid where it stays until it is reabsorbed by the late proximal tubule / thin descending limb of the loop of Henle. This potassium field decreases the amount of sodium reabsorbed proximal to the distal tubule (specifically in the thick ascending limb by the Na/K/2Cl transporters), ensuring enough sodium is available for significant potassium reabsorption if necessary.
How do alpha intercalated cells reabsorb potassium?
Carbonic anhydrase breaks down carbonic acid into hydrogen and bicarbonate. Bicarbonate is reabsorbed, and the hydrogen is excreted in exchange for a reabsorbed potassium.
How do principal cells secrete potassium?
They reabsorb a sodium ion via the ENaC channel, and then exchange that sodium for a potassium ion which is secreted through Big Potassium, and Renal Outer Medullary Potassium channels.
When we increase our sodium intake, aldosterone compensates.
What will be the effect of that compensation on potassium, and why doesn’t it make us hypo/hypokalemic?
When we increase sodium intake, aldosterone decreases to compensate.
This decrease in aldosterone increases reabsorption of potassium.
However, we don’t become hyperkalemic because the increase in sodium also increases the tubular flow rate in the distal tubule.
The increase in tubular flow rate washes out potassium and increases potassium secretion to balance the increased reabsorption.
What is the effect of acute acidosis on potassium?
The increased acid inactivates the Na/K ATPase, decreasing the amount of sodium reabsorbed and the amount of potassium excreted.
This causes hyperkalemia.
What is the effect of glucocorticoids and increased anion delivery on potassium secretion?
Glucocorticoids and increased anion delivery both increase potassium secretion by increasing fluid flow rate.
(The anions act as an osmotic diuretic – glucocorticoids directly increase GFR by binding to the same receptor as aldosterone)
How do beta-intercalated cells secrete potassium?
Hydrogen is produced inside the cell by the action of carbonic anhydrase breaking down carbonic acid into hydrogen and bicarbonate (the latter of which is excreted). That hydrogen ion is then reabsorbed in exchange for a potassium ion, which is excreted.
How would systemic alkalosis / acidosis affect plasma potassium levels?
Alkalosis would cause potassium to enter the cells in exchange for hydrogen, thereby creating hypokalemia (low plasma potassium)
Acidosis would cause potassium to exit the cells in exchange for hydrogen, thereby creating hyperkalemia (high plasma potassium)
What is the function of epinephrine in potassium balance?
Epinephrine lowers serum potassium by encouraging uptake into extrarenal tissue cells.
Epinephrine’s alpha-1 receptors also encourage potassium excretion by the kidney, via stimulation of the Na/K ATPase – encouraging potassium to enter peritubular cells where potassium channels can secrete it into the urine.
What is the function of insulin in potassium balance?
Insulin (like epinephrine) stimulates Na/K ATPase, causing potassium to enter the peritubular cells where it can then be ejected by potassium channels.
Why might decreased flow rate decrease potassium secretion?
Decreased flow rate causes potassium to buildup in the intratubular fluid, which decreases the concentration gradient, making it harder to push potassium into the intratubular fluid.
How is potassium reabsorbed by the proximal tubule?
Sodium is reabsorbed with bicarbonate leaving chloride behind, this creates a negative transepithelial potential difference. When chloride is reabsorbed paracellularly, this creates a positive transepithelial potential difference. That positive TEPD pushes potassium between the cells – paracellular reabsorption.
Is hypokalemia typically associated with systemic acidosis, or alkalosis?
Hypokalemia is typically associated with systemic alkalosis.
(Aldosterone gets rid of potassium, and also causes alkalosis)
