Potassium and more L16 Flashcards
what is the normal intracellular concentration of K+?
140mM
what is the normal extracellular concentration of K+?
4mM
At what point is the cellular equilibrium of K+ reached? What is this value normally? (think back to Nernst equation)
will be reached when
([K+]intracellularly) / ([K+]extracellularly) is constant i.e. reaches a value and remains at that value.
Normally this ratio would be 140/4 (=35)
If more K+ ions are added to the extracellular space, some will move into the intracellular space and a new equilibrium will form. How would we calculate what this new equilibrium would be and how many K+ ions have moved intracellularly?
- denote the amount of K+ ions moving intracellularly as x mmol
- figure out the new intracellular and extracellular K+ concentrations in terms of x
- the new equilibrium will be formed when the ratio of K+ concentrations is the same as the start/normal value
- therefore it should equal 140/4
- form the equation and solve to find x telling you how many K+ ions have moved and thus the new equilibrium
*if still don’t understand look at first page of lecture handout
what are the causes of hyperkalaemia?
- end stage renal failure
- crush injuries
- blood transfusion (rbcs leak K+ after long time in storage)
- cytotoxic drugs
- insulin deficiency
- overuse of K+ sparing diuretics
How do K+ sparing diuretics work?
work to decrease water reabsorption without increasing K+ secretion.
two mechanisms:
- competitive antagonists with aldosterone for intracellular cytoplasmic receptor sites
- directly block sodium (ENaC) channels
for 1, preventing aldosterone reaction from occurring so Na+/K+ exchange in collecting tubule does not occur so Na+ not reabsorbed and K+ not secreted
Why does insulin deficiency cause hyperkalaemia?
- insulin increases rate of k+/Na+ ATPase
- allows more K+ to enter cells
- therefore insulin deficiency leads to more K+ in extracellular space > hyperkalaemia
What are treatments for hyperkalaemia?
-treat the cause
-K+ restricted diet
-insulin + glucose(to stimulate insulin release)
-
What are causes of hypokalaemia?
- diarrhoea
- furosemide
- insulin overdose
What are treatments for hypokalaemia?
- give K+ (IV if acute, oral if chronic)
- treat the cause
- aldosterone antagonists (K+ sparing diuretics - spironolactone)
What are the functions of aldosterone?
- volume regulation - RAAS
- main hormone for regulating K+ concentration in the body
Describe Ca2+ filtration through the nephron.
- PT: moves transcellularly into interstitial space (channels on apical, active on basolateral). Ca2+ movement proportions to water movement
- TAL: paracellular reabsorption into tubule driven by positive potential in lumen of TAL (due to Na+/K+ transporter and K+ recycling)
Describe sulfate reabsorption in the nephron.
- mainly reabsorbed in PT
- uses Na+ gradient/ Na-dependent apical cotransporter
- apical co-transporter = NaS1 - tranports 3Na+ with 1 sulphate ion
- basolateral surface has anion exchangers that transport sulphate into interstitium
what happens when there is an absence of the NaS1 transporter?
-high sulphate in urine (hypersulfaturia) /low plasma sulfate (hyposulfatemia)
is sulphate reabsorption Tm limited?
yes
