6.2 K balance renal control

Question 1

Interactions between acid-base status and plasma [K+]

Question 2

Explain how K handling occurs in the various segments of the nephron

Question 3

1. Majority (approx 98%) of the 3500 mEq of k+ within body is located within where ?
2. only 2% found where ?

Answer 3

1. cells
2. extracellular fluid

Question 4

1. Intracellular [k+] = ~ … mmol/L
2. extracellular [k+] = ~… mmol/L

Answer 4

1. 150
2. 4

Question 5

Why is most K+ found intracellularly ?

Question 6

What is role of potassium [k+] in the body ?

Answer 6

major determinant of intracellular osmolarity
ratio of [k+] ECF: ICF influences cell membrane polarisation

Question 7

why is it important to maintain normokalaemia ?

Answer 7

small changes in plasma [k+] can have significant clinical implications
e.g. conduction of nerve impulses to skeletal muscle (muscle weakness) , cardiac action potentials (arrhythmias)

Question 8

What factors affect ECF [K+] ? medium to long-term …

Answer 8

…

Question 9

What factors affect ECF [K+] ?short term …

Question 10

What is K+ concentration in the extracellular fluid (ECF) is affected by ?

Answer 10

• dietary intake
• exchange with the intracellular fluid (ICF)
• urinary excretion

Question 11

values of ECF [K+] in the following:
1. hyperkalaemia
2. normokalaemia
3. hypokalaemia

Answer 11

1. > 5.0 mmol/L
2. 3.5-5.0 mmol/L
3. < 3.5 mmol/L

Question 12

Effects of hyperkalaemia & hypokalaemia on excitable tissues ….

Answer 12

slide 9/22

Question 13

Movement of K+ between the cells and the ECF depends on factors including what ?

Answer 13

• insulin concentration
• Beta 2 - adrenergic activity
• acid-base status

Question 14

K+ moved from ECF into cells following what ?

Answer 14

insulin/adrenaline-stimulated activation of Na+/K+-ATPase

Question 15

Give examples of how the release of small amounts of k+ from cells can INC [k+] ?

Answer 15

• insulin deficiency
• cell lysis
• severe exercise

Question 16

INC [H+] ions causes what in cells ?

Answer 16

Uptake of H+ into cells and intracellular buffering, to some extent, in exchange for K+

Question 17

Effect of [K+] in ECF in acidosis and alkalosis happens why ?

Answer 17

acidosis = INC [k+]
alkolosis DEC [k+]

• INC [H+] ions causes uptake of H+ into cells , where to some extent in exchange for K+

Question 18

Potassium handling in the nephron ?

Question 19

what can elevated plasma [K+] directly induce ?

Answer 19

aldosterone release

Question 20

1. INC aldosterone stimulates what ?
2. INC aldosterone facilitates what ?

Answer 20

1. Na/K- ATPase expression (and therefore ↑ K+ uptake into cells)
2. K+ secretion via ROMK channels following Na+ uptake (via ENaC channels)

Question 21

Action of aldosterone on principle tubular cells of the cortical collecting duct ?

Answer 21

• ROMK
• ENaC
• MR
• …

Question 22

Interaction between pH and K+ ???

Question 23

What does acute metabolic acidosis cause K+ to do ?

Answer 23

move out of cells

Question 24

What does acute metabolic alkalosis cause K+ to do ?

Answer 24

move into cells

Question 25

What in ECF may be more important than changes in pH ?

Answer 25

[HCO3-]

Question 26

Why does the hyperkalaemia common in diabetic ketoacidosis result more from insulin deficiency than from acidosis ? [I DON'T GET HTIS !!!!!]

Answer 26

non-anion gap (hyperchloraemic) metabolic acidosis causes INC K+ In contrast, metabolic acidosis organic acids (INC anion gap acidosis) does NOT cause hyperkalaemia

Question 27

What affects serum potassium concentraiton less than metabolic acidosis and alkalosis ?

Answer 27

acute respiratory acidosis and respiratory alkalosis

Question 28

Insulin stiumlates cellular uptake of K+ ...

Question 29

Apart from insulin what else can also induce cellular uptake of K+

Answer 29

thyroxine and beta-adrenergic stimulation

Question 30

What happens to potassium in the distal tubule ?

Answer 30

* secreted by principal cells * reabsorbed by type-A-intercalated cells which balance between the 2 determines ECF [K+]

Question 31

Movement of what is dependent on maintaining a low [K+] in the filtrate (concentration gradient) ?

Answer 31

* Na/K-ATPase drives K+ secretion from principal cells into the tubular filtrate via ROMK channels.

Question 32

Na/K-ATPase drives K+ secretion from principal cells into the tubular filtrate via ROMK channels what is this movement sitmulated by ?

Answer 32

* High ECF [K+] * Aldosterone * High ECF pH * High GFR (high flow quickly removes secreted K+ and ‘steepens’ the K+ concentration gradient).

Question 33

What is K+ reabsorption via alpha-intercalated cells driven by ?

Answer 33

H+/K+ ATPase exchanger * driven by pH of ECF * low ECF pH more K+ absorbed * high ECF pH less K+ absorbed * K+ exits the cell via basolateral K+ channels

Question 34

Causes of hypokalaemia can include ?

Answer 34

* diuretics (e.g. K+ sparing ? , aldosterone antagonists) * hypokalaemia associated with vomiting * renal tubular acidoses * some antibiotics (e.g. penicillins and aminoglycosides) * insulin excess or overdose * mutations in the NK2Cl transporter

Question 35

causes of hyperkalaemia can include ?

Answer 35

* rhabdomyolysis * insulin deficiency * metabolic acidosis * hypoaldosteronism * ACE inhibitors * pseudohypoaldosteronism

Question 36

Why could rhabdomyolysis cause hyperkalaemia ?

Question 37

Hypoaldosteronism can cause hyperkalaemia as a result of what ? why ?

Answer 37

potassium-sparing diuretics ...

Question 38

Can you think why ACE inhibitors could cause hyperkalaemia ?

Question 39

Why can pseudohypoaldosteronism cause hyperkalaemia ?

Answer 39

an inactivating mutation in ENaC channels

Question 40

clinical features of hypokalaemia

Question 41

clinical features of hyperkalaemia