Potassium Balance and Renal Transport Flashcards
(20 cards)
Say you eat a bunch of K+, why does your plasma [K+] only increase a little?
Most of it rapidly moves into cells, renal excretion of K+ happens more slowly.
Normal plasma [K+]?
4-5 mEq/L
Can cells better buffer a K+ deficit or excess?
They can better buffer a deficit, as K+ can move out of cells, but they can’t take up much extra.
If there weren’t cellular uptake, eating 5ish bananas would be lethal.
Ok.
3 hormones that affect “internal” K+ balance?
Insulin
Catecholamines
Aldosterone
How do insulin, catecholamines, and aldosterone all affect plasma [K+]?
They decrease it by stimulating that Na+/K+ ATPase.
How do exercise and cell lysis affect ECF [K+]?
They increase it.
How does ECF hypertonicity affect ECF K+? How?
Example of when this happens?
ECF tonicity causes movement of water out of cells.
K+ follows the water via solvent drag.
This can happen with hyperglycemia in diabetics.
How can acidemia cause acute hyperkalemia?
High levels of H+ can bind to pumps/channels normally occupied by K+.
Acidemia -> hyperkalemia.
Alkalemia -> hypokalemia.
This makes sense… because high ECF H+ will displace some intracellular K+, and vice versa.
2 ways K+ is eliminated?
feces, urine
Where in the nephron is most K+ reabsorbed, at fixed rates?
80% in the proximal tubule.
Another 10% in thick ascending limb…
Where in the nephron is K+ excretion/reabsorption regulated?
After the thick ascending limb…
The 2 different cell types in the collecting duct have different effects on K+. Which does which?
Principal cells: K+ secretion.
Intercalated cells: K+ reabsorption.
How do alpha-intercalated cells reabsorb K+?
K+/H+ ATPase (moves K+ in, H+ out into lumen)
How do principal cells secrete K+?
K+/Cl- cotransporter moves it into lumen.
4 factors affecting distal tubule K+ secretion?
K+ intake, plasma [K+].
Aldosterone.
Distal tubule Na+ and flow.
Anions in tubular fluid.
How does flow through distal tubule affect how much K+ is secreted? Why?
More distal tubule flow, more K+ secretion for any level of intake.
More Na+ removed -> more K+ moved into lumen.
Why won’t eating lots of Na+ make you hypokalemic?
Because aldosterone will be inhibited.
Why might sodium sulfate, if you gave it, cause hypokalemia?
Poorly absorbed anions will draw K+ into the tubule.
This applies to some drugs (and NaHCO3 at levels exceeding reabsorption capacities).
