Regulation of plasma K+ Flashcards
What percent of K+ is intracellular and why?
98% due to Na/K ATPase
What range is K+ tightly regulated in plasma?
3.5-5 mM
Is K+ a major determinant of voltage difference in excitable or unexcitable cells?
both
In hyperkalemia: depolarization or hyperpolarization? hyperexcitability or hypoexcitability? how does it affect the heart? metabolic acidosis or alkalosis?
depolarized
hyperexcitability
ventricular arrythmia and fibrillation
metabolic acidosis
In hyperkalemia: depolarization or hyperpolarization? hyperexcitability or hypoexcitability? how does it affect the heart? metabolic acidosis or alkalosis?
hyperpolarization
hypoexcitability
arrythmias - bradycardia
metabolic alkalosis
How is k+ balanced externally?
renal and fecal removal of k+ from the body
amout of K+ consumed must equal amount excreted
-kidney is main regulator
What is the equation for the renal handling of K?
excreted = filtered-reabsorbed+ secreted
What is the main regulator of K+ internally?
NaKATPase
What organ is most K+ located in?
muscle
What is the bodie’s first line of defense against hyperkalemia?
inc uptake into cells
-sequestration by Na/K ATPase
What three hormones promote cellular uptake of K+, and how do they do this?
epinephrine
aldosterone
insulin
-promote de novo synthesis of NaKATPase
Do RBCs respond to hormones to inc K+ uptake?
N0O0O they don’t have nuclei and cant make proteins
Are diabetics more likely to be hyperkalemic or hypokalemic?
hyperkalemic
-dysregulation of insulin - cant take up the extra K+
How does a high K+ plasma concentration affect uptake in the GI tract?
it DOESN’T
GI tract absorption is constitutive
When a high load of K+ is introduced, how do the cell’s respond? how does the kidney respond?
cell’s respond quick and uptake K+ rapidly
kidney’s response is more slow and eventually inc secretion and dec reabsorption
eventually excretion of K+ will occur even when there is not elevated plasma K+
Where is most K+ reabsorbed?
proximal tubule -80% at a constitutive rate
Where is reabsorption or secretion of K+ regulated?
distal nephron - distal tubule and cortical collecting duct
How much of K+ is reabsorbed at loop of henle?
10% - not regulated
What percent of the filtered load is the kidney able to secrete in times of hyperkalemia?
10-150%
How is the renal handling of Na different from K+
Na+ - no secretion occurs
-old diet’s didnt have much salt
What occurs to K+ in the proximal tubule and by what method?
reabsorption
paracellular
What drives the paracellular reabsorption of K+ in the early and late proximal tubule?
early: active transcellular Na+ transport drives net fluid reabsorption by osmosis
late: transepithelial voltage is positive
- driving force for K+
how does the Na/K ATPase in the proximal tubule contribute to paracellular reabsorption of k+ ?
it doesn’t!
What occurs to K+ in the thick ascending loop of henle and by what method?
reabsorption
transcellular and paracellular
What drives paracellular transport in the thick ascending loop of henle?
lumen positive voltage difference
What drives the transcellular reabsorption in the thick ascending loop of henle?
membrane specific transporters
luminal: na/k/2cl cotransporter transport these ions in
basolateral: Cl, K+ transporters and Na/K ATPase
A small amount of K+ effluxes into the lumen through K+ channels, what does this provide a driving force for?
ca and Mg reabsorption
What occurs to K+ in the distal nephron and by what method?
secretion or reabsorption
transcellularly
How does transcellular k+ reabsorption in the distal nephron occur?
K/H ATPase
actively transports K into cell and H out
How does transcellular K+ secretion occur in the distal nephron?
active transport basolaterally
passive transport luminally
When flow rates are high in the distal nephron, how is K+ secretion affected?
K+ secretion is able to be much higher
-K+ is swept away as fast as it is transported out driving secretion
What is a major complication of diuretics?
hyperkalemia
In the distal nephron what is K+ secretion coupled to?
Na+ reabsorption
What are the three effects of aldosterone?
- inc synthesis of Na/K ATPase
- inc prodution of Na and K+ channels
- inc production of mito enzymes
What is the relationship btwn alkalosis, acidosis, hyperkalemia and hypokalemia?
alkalosis hypokalemia
acidosis hyperkalemia
needs to be delicate balance btwn H/K ATPase function
