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PHSL233 > Lecture 21 - Renal handling of potassium > Flashcards

Lecture 21 - Renal handling of potassium Flashcards

1
Q

What is the concentration of K+ in the ICF and the ECF?

A

ICF - generally 150 mM
ECF ~ 4 mM

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2
Q

What happens when ECF > 5 mM?

A

Hyperkalaemia (High K+ blood)

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3
Q

What happens when ECF < 3.5 mM?

A

Hypokalaemia (Low K+ blood)

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4
Q

What ion must be highly regulated in renal handling?

A

K+

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5
Q

Why is high K+ in the ICF important? (5)

A
  • maintain cell volume
  • regulation of pH
  • controlling cell enzyme function
  • controlling DNA and protein synthesis
  • controlling cell growth, cell cycling and cell proliferation
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6
Q

Why is low K+ in the ECF important? (2)

A

Maintain the steep K+ gradient across the membrane to maintain the potential of cells

Low K+ prevents problems with excitation and contraction

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7
Q

What excitation and contraction problems does low K+ in ECF prevent?

A

– action potential
– muscle contraction
– cardiac rhythmicity

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8
Q

What is the effect of low K+ ECF on the nerve action potential?

A

Decreases membrane potential (more negative) meaning its harder to reach threshold for AP

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9
Q

What is the effect of high K+ ECF on the nerve action potential?

A

Increases RMP (less negative) meaning it is easier to reach threshold for AP

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10
Q

What would happen to you if the K+ in your ECF was reduced to 2.5 mM?

A

We would have hypokalaemia which effects heart contractions causing:
Low T wave
High U wave
Low ST segment

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11
Q

What happens at the P wave in ECG?

A

Atrial depolarisation

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12
Q

What happens at the T wave in ECG?

A

Ventricular repolarisation

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13
Q

What is the ST segment in ECG?

A

The ST segment encompasses the region between the end of ventricular depolarization and beginning of ventricular repolarization on the ECG.

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14
Q

What would happen to you if the K+ in your ECF increased as high as 10 mM?

A

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

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15
Q

What has a greater effect on heart contractions, ECF K reduced to 2.5mM or ECF increased to 10mM?

A

Extra K+ has more drastic changes in ECG than less K+

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16
Q

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.

A

C. K+ is the most abundant cation in the body.

17
Q

What happens to K+ balance when Intake > Excreted

A

+ K+ balance

18
Q

What happens to K+ balance when Intake < Excreted

A
  • K+ balance
19
Q

How does our body respond to changes in K+ to maintain K+ homeostasis?

A

Extrarenal - to increase K+ uptake into cells
Intrarenal - regulation of reabsorption and
secretion of K+ along the nephron

20
Q

How long does our body react to changes in K+ via the extrarenal pathway vs intrarenal?

A

Extrarenal - Rapidly
Intrarenal - Over several hours

21
Q

What 3 hormones are used in the extrarenal response to changes in K+ and how?

A

epinephrine
insulin
aldosterone
All three hormones increase amount of K+ pumped / increase activity of Na/K- ATPase

22
Q

How does epinephrine increase uptake of K+ into cells?

A

Epinephrine released from the chromaffin cells from the adrenal medulla increases Na+-K+-ATPase activity by increasing cAMP

23
Q

How does insulin increase uptake of K+ into cells?

A

Insulin released from the b-cells of the pancreas increases Na+-K+-ATPase activity

24
Q

How does aldosterone increase uptake of K+ into cells?

A

Aldosterone released from the zona glomerulosa cells from the adrenal cortex increases Na+/K+-ATPase activity

25
Q

Why do we have multiple extrarenal response pathways to changes in K+?

A

Mulitple systems to maintain high K+ in ICF and low K+ in ECF

26
Q

What is the overall handling of K+ by the nephron during K+ depletion (hypokalaemia)?

A

K+ is only reabsorbed (no secretion)
PT 67%
TAL 20%
DT 3%
CCD 9%
IMCD 1%

27
Q

What is the overall handling of K+ by the nephron during normal and increased K+ (hyperkalaemia)?

A

PT 67% reabsorption
TAL 20% reabsorption
DT 10-50% secretion
CCD 5-30% secretion
IMCD 15-80% secretion

28
Q

What areas of the nephron change from reabsorption to secretion during changes in K+?

A

DT
CCD
IMCD

29
Q

What is CCD?

A

Cortical collecting duct

30
Q

What is IMCD?

A

Inner medullary collecting duct

31
Q

What % of K+ does the PT reabsorb and how?

A

67% of K+ reabsorption
Mainly paracellularly

32
Q

What % of K+ does the TAL reabsorb and how?

A

20% of K+ reabsorption
Via the cellular (Na+-K+-2Cl- cotransporter) and paracellular pathways

33
Q

What two cells does the CCD contain?

A

Intercalated cells 30%
Principal cells 70%

34
Q

What is the intercalated cell role in K+ regulation?

A

9% of K+ reabsorption via the K+/H+-ATPase

35
Q

What is the principal cells role in K+ regulation?

A

Na+ reabsorption and K+ secretion (luminal K+ channel) under the influence of aldosterone and the K+-Cl- cotransporter

36
Q

What is CA?

A

Carbolic anhydrase - important for pH balance in cells

37
Q

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.

A

B. Your body would reduce insulin release to reduce uptake of K+ into cells.

38
Q

What are the overall factors that effect K+ excretion (secretion)?

A
  • high plasma K+ concentrations
  • aldosterone
  • flow rate of the filtrate
39
Q

What is the effect of Aldosterone on K+ secretion by the LDT and CD

A

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)

PHSL233 (32 decks)

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