Potassium Flashcards
what is the average intracellular concentration of potassium?
150 mEq/L
What is the normal concentration of potassium in the ECF?
4 mEq/L
range: 3.5 to 5
What concentration of potassium in the ECF defines hyperkalemia?
> 5 mEq/L
What concentration of potassium in the ECF defines hypokalemia?
< 3.5 mEq/L
Which hormones promote the uptake of potassium by cells?
epinephrine and insulin - stimulate the ATPase pump
What triggers insulin secretion by the pancreas and epinephrine secretion by the adrenal medulla?
. A rise in plasma [K+], subsequent to K+ absorption by the gastrointestinal tract
In regards to diet, what is the most important hormone regulating potassium concentration?
insulin
Why is rapid uptake by the cells important in preventing life threatening hyperkalemia following a meal?
If the K+ ingested during a normal meal ( 33 mEq) were to remain in the ECF compartment, plasma [K+] would increase by a potentially lethal 2.4 mEq/l. The rapid uptake of K+ into the cells prevents this rise in plasma [K+]. As the excretion of K+ by the kidneys after a meal is relatively slow (hours), the rapid uptake of K+ by the cells is essential to prevent life-threatening hyperkalemia
What effect would low K have on the resting potential of a cell?
lower it, making it less excitable
What effect would high K have on the resting potential of a cell?
increase it, making it more excitable
What is true of K intake and excretion?
it is equal within a tenfold range
How is most K excreted?
via the renal system
What is the primary event that trigers urinary potassium excretion?
is K+ secretion from the blood into the tubular fluid by the cells of the distal tubule and collecting duct system.
Potassium is freely filtered by the glomerulues, true or false. why?
true - not bound to protein
When potassium intake is normal, what is true of potassium handling by the CCD?
it is secreting K
What effect would a low potassium diet have on the distal tubule and collecting duct?
a low-potassium diet activates K+ reabsorption along the distal tubule and collecting duct so that the urinary excretion falls to 1% of the K+ filtered by the glomerulus
Why is hypokalemia somewhat easier to develop due to dietary changes than hyponatremia?
the kidneys are not able to reduce K excretion by the same degree as it can na
What are the main factors controlling the rate of K secretion by the distal renal tubule and collecting duct?
- The activity of the Na+/K+ ATPase pump in the collecting tubule
- The driving force (electrochemical gradient) for K+ movement across the apical membrane, which is influenced by urine flow rate
- The ability of K+ to cross the apical membrane (potassium conductance) via a K+ channel called ROMK
- The ability of the Na+ channels to function thereby, creating a favorable electrical gradient for potassium secretion.
- Aldosterone which increases the activity of the Na+ K+ ATPase pump and opens the sodium channel.
What are the 3 main physiologic regulators of potassium secretion?
plasma K, aldosterone, distal Na delivery
What 3 factors can perturb K secretion?
- aldosterone levels
- flowof tubular fluid and distal sodium delivery
- acid base balance
What effect does alkalosis have on K secretion?
increase it
what effect does acidosis have on K secretion?
decreases it
what effect does chronic renal insufficiency have on potassium excretion?
The development of chronic renal insufficiency is associated with renal adaptation such that the quantity of potassium excreted per nephron is increased. This permits a normal absolute potassium excretion despite reduced GFR. Eventually, the mechanism for potassium adaptation is overwhelmed, and the absolute quantity of potassium excreted is less than potassium intake. Thus, hyperkalemia is expected whenever glomerular filtration fate (GFR) is markedly reduced (less than 10 mL/minute).
What is the GFR at which hyperkalemia is expected ?
< 10 mL/min
