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
