Renal potassium balance Flashcards
What is the physiology of potassium metabolism?
- Potassium intake
-Diet (70-150mmol/day) - Absorption
-GI tract - Distribution
-ICF (98%)
-ECF (2%)
What is the normal plasma K+ range in the ECF?
Normal plasma K+ range: 3.5 to 5.5mmol/L
What is hypokalaemia?
low potassium, <3.5 mmol/L
What can cause hypokalaemia?
- Drugs e.g. diuretics
- GI loss
- Mineralocorticoid excess
- Genetic disease (Gitelmans and Bartters)
What is hyperkalaemia?
Hyperkalaemia (raised potassium, >5.5 mmol/L)
What can cause hyperkalaemia?
- Drugs e.g. potassium sparing diuretics, ACEi or ARBs,
- CKD/ESKD
- Addison’s
- Food ingestion
What are the 4 mechanisms of K+ balance?
- K+ intake through diet
- GI losses
- GI tract secretes 5-10% of absorbed K+ daily - Renal losses
-90-95% is regulated by the kidney - Transcellular K+ shift
- Overall K+ stores remain the same but redistribute
between the ICF and ECF
How much K+ is reabsorbed in PCT?
Reabsorbs 65-70% of filtered K+
What process is K+ reabsorption via in PCT?
K+ reabsorption is via diffusion and solvent drag
What percentage of K+ does the thick ascending loop of henle reabsorb?
Re-absorbs 10-25% of K
What is the active transporter affinity like when tubular K+ fluid are low in thick ascending loop of henle?
Transporter affinity for Na+, K+ high when tubular fluid K are low
How does K absorption occur in DCT and CD?
Occurs via a transcellular pathway and is mediated by alpha and beta
intercalated cells
What do intercalated cells do in DCT and CD?
Reabsorb K+
What are the 2 steps of reabsorption of potassium ?
- The apical H+-K+-ATPase mediates the movement of H+ into
the lumen, driving K+ into the intercalated cell - Then, the basolateral K+ channel allows the K+ inside the intercalated cell to
leak out into the bloodstream.
What is the primary regulatory site of K+ excretion?
Principal Cell