Lecture 21 - Renal handling of potassium Flashcards
What is the concentration of K+ in the ICF and the ECF?
ICF - generally 150 mM
ECF ~ 4 mM
What happens when ECF > 5 mM?
Hyperkalaemia (High K+ blood)
What happens when ECF < 3.5 mM?
Hypokalaemia (Low K+ blood)
What ion must be highly regulated in renal handling?
K+
Why is high K+ in the ICF important? (5)
- maintain cell volume
- regulation of pH
- controlling cell enzyme function
- controlling DNA and protein synthesis
- controlling cell growth, cell cycling and cell proliferation
Why is low K+ in the ECF important? (2)
Maintain the steep K+ gradient across the membrane to maintain the potential of cells
Low K+ prevents problems with excitation and contraction
What excitation and contraction problems does low K+ in ECF prevent?
– action potential
– muscle contraction
– cardiac rhythmicity
What is the effect of low K+ ECF on the nerve action potential?
Decreases membrane potential (more negative) meaning its harder to reach threshold for AP
What is the effect of high K+ ECF on the nerve action potential?
Increases RMP (less negative) meaning it is easier to reach threshold for AP
What would happen to you if the K+ in your ECF was reduced to 2.5 mM?
We would have hypokalaemia which effects heart contractions causing:
Low T wave
High U wave
Low ST segment
What happens at the P wave in ECG?
Atrial depolarisation
What happens at the T wave in ECG?
Ventricular repolarisation
What is the ST segment in ECG?
The ST segment encompasses the region between the end of ventricular depolarization and beginning of ventricular repolarization on the ECG.
What would happen to you if the K+ in your ECF increased as high as 10 mM?
We would have hyperkalaemia which effects heart contractions causing: Ventricular fibrillation (type of arrhythmia) which can lead to death
Additional:
High T wave
Prolonged PR interval
Depressed ST segment
What has a greater effect on heart contractions, ECF K reduced to 2.5mM or ECF increased to 10mM?
Extra K+ has more drastic changes in ECG than less K+
Which of the following statements is TRUE?
A. A typical diet does not contain the proper amount of daily K+.
B. Low ICF K+ is very important for proper enzyme function.
C. K+ is the most abundant cation in the body.
D. K + is not involved in the nerve action potential.
C. K+ is the most abundant cation in the body.
What happens to K+ balance when Intake > Excreted
+ K+ balance
What happens to K+ balance when Intake < Excreted
- K+ balance
How does our body respond to changes in K+ to maintain K+ homeostasis?
Extrarenal - to increase K+ uptake into cells
Intrarenal - regulation of reabsorption and
secretion of K+ along the nephron
How long does our body react to changes in K+ via the extrarenal pathway vs intrarenal?
Extrarenal - Rapidly
Intrarenal - Over several hours
What 3 hormones are used in the extrarenal response to changes in K+ and how?
epinephrine
insulin
aldosterone
All three hormones increase amount of K+ pumped / increase activity of Na/K- ATPase
How does epinephrine increase uptake of K+ into cells?
Epinephrine released from the chromaffin cells from the adrenal medulla increases Na+-K+-ATPase activity by increasing cAMP
How does insulin increase uptake of K+ into cells?
Insulin released from the b-cells of the pancreas increases Na+-K+-ATPase activity
How does aldosterone increase uptake of K+ into cells?
Aldosterone released from the zona glomerulosa cells from the adrenal cortex increases Na+/K+-ATPase activity
Why do we have multiple extrarenal response pathways to changes in K+?
Mulitple systems to maintain high K+ in ICF and low K+ in ECF
What is the overall handling of K+ by the nephron during K+ depletion (hypokalaemia)?
K+ is only reabsorbed (no secretion)
PT 67%
TAL 20%
DT 3%
CCD 9%
IMCD 1%
What is the overall handling of K+ by the nephron during normal and increased K+ (hyperkalaemia)?
PT 67% reabsorption
TAL 20% reabsorption
DT 10-50% secretion
CCD 5-30% secretion
IMCD 15-80% secretion
What areas of the nephron change from reabsorption to secretion during changes in K+?
DT
CCD
IMCD
What is CCD?
Cortical collecting duct
What is IMCD?
Inner medullary collecting duct
What % of K+ does the PT reabsorb and how?
67% of K+ reabsorption
Mainly paracellularly
What % of K+ does the TAL reabsorb and how?
20% of K+ reabsorption
Via the cellular (Na+-K+-2Cl- cotransporter) and paracellular pathways
What two cells does the CCD contain?
Intercalated cells 30%
Principal cells 70%
What is the intercalated cell role in K+ regulation?
9% of K+ reabsorption via the K+/H+-ATPase
What is the principal cells role in K+ regulation?
Na+ reabsorption and K+ secretion (luminal K+ channel) under the influence of aldosterone and the K+-Cl- cotransporter
What is CA?
Carbolic anhydrase - important for pH balance in cells
If you have a low K+ diet, which statement is TRUE?
A. Your body would increase K+ secretion by the collecting duct cells.
B. Your body would reduce insulin release to reduce uptake of K+ into cells.
C. Your body would increase the release of epinephrine to increase uptake of K+ into cells.
D. Your body would increase the amount of aldosterone.
B. Your body would reduce insulin release to reduce uptake of K+ into cells.
What are the overall factors that effect K+ excretion (secretion)?
- high plasma K+ concentrations
- aldosterone
- flow rate of the filtrate
What is the effect of Aldosterone on K+ secretion by the LDT and CD
Increased activation and amount of ENaC
Increased amount and activity of the Na+-K+-ATPase; entry of K+ across basolateral membrane
Entry of Na+ makes the cell potential more positive enhancing the driving force for K+ exit across the apical membrane (K+ secretion)
