6.2 K balance renal control Flashcards
Interactions between acid-base status and plasma [K+]
Explain how K handling occurs in the various segments of the nephron
- Majority (approx 98%) of the 3500 mEq of k+ within body is located within where ?
- only 2% found where ?
- cells
- extracellular fluid
- Intracellular [k+] = ~ … mmol/L
- extracellular [k+] = ~… mmol/L
- 150
- 4
Why is most K+ found intracellularly ?
What is role of potassium [k+] in the body ?
major determinant of intracellular osmolarity
ratio of [k+] ECF: ICF influences cell membrane polarisation
why is it important to maintain normokalaemia ?
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)
What factors affect ECF [K+] ? medium to long-term …
…
What factors affect ECF [K+] ?short term …
What is K+ concentration in the extracellular fluid (ECF) is affected by ?
- dietary intake
- exchange with the intracellular fluid (ICF)
- urinary excretion
values of ECF [K+] in the following:
1. hyperkalaemia
2. normokalaemia
3. hypokalaemia
- > 5.0 mmol/L
- 3.5-5.0 mmol/L
- < 3.5 mmol/L
Effects of hyperkalaemia & hypokalaemia on excitable tissues ….
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Movement of K+ between the cells and the ECF depends on factors including what ?
- insulin concentration
- Beta 2 - adrenergic activity
- acid-base status
K+ moved from ECF into cells following what ?
insulin/adrenaline-stimulated activation of Na+/K+-ATPase
Give examples of how the release of small amounts of k+ from cells can INC [k+] ?
- insulin deficiency
- cell lysis
- severe exercise
INC [H+] ions causes what in cells ?
Uptake of H+ into cells and intracellular buffering, to some extent, in exchange for K+
Effect of [K+] in ECF in acidosis and alkalosis happens why ?
acidosis = INC [k+]
alkolosis DEC [k+]
- INC [H+] ions causes uptake of H+ into cells , where to some extent in exchange for K+
Potassium handling in the nephron ?
what can elevated plasma [K+] directly induce ?
aldosterone release
- INC aldosterone stimulates what ?
- INC aldosterone facilitates what ?
- Na/K- ATPase expression (and therefore ↑ K+ uptake into cells)
- K+ secretion via ROMK channels following Na+ uptake (via ENaC channels)
Action of aldosterone on principle tubular cells of the cortical collecting duct ?
- ROMK
- ENaC
- MR
- …
Interaction between pH and K+ ???
What does acute metabolic acidosis cause K+ to do ?
move out of cells
What does acute metabolic alkalosis cause K+ to do ?
move into cells
What in ECF may be more important than changes in pH ?
[HCO3-]
Why does the hyperkalaemia common in diabetic ketoacidosis result more from insulin deficiency than from acidosis ? [I DON’T GET HTIS !!!!!]
non-anion gap (hyperchloraemic) metabolic acidosis causes INC K+
In contrast, metabolic acidosis organic acids (INC anion gap acidosis) does NOT cause hyperkalaemia
What affects serum potassium concentraiton less than metabolic acidosis and alkalosis ?
acute respiratory acidosis and respiratory alkalosis
Insulin stiumlates cellular uptake of K+ …
Apart from insulin what else can also induce cellular uptake of K+
thyroxine and beta-adrenergic stimulation
What happens to potassium in the distal tubule ?
- secreted by principal cells
- reabsorbed by type-A-intercalated cells
which balance between the 2 determines ECF [K+]
Movement of what is dependent on maintaining a low [K+] in the filtrate (concentration gradient) ?
- Na/K-ATPase drives K+ secretion from principal cells into the tubular filtrate via ROMK channels.
Na/K-ATPase drives K+ secretion from principal cells into the tubular filtrate via ROMK channels
what is this movement sitmulated by ?
- High ECF [K+]
- Aldosterone
- High ECF pH
- High GFR (high flow quickly removes secreted K+ and ‘steepens’ the K+ concentration gradient).
What is K+ reabsorption via alpha-intercalated cells driven by ?
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
Causes of hypokalaemia can include ?
- 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
causes of hyperkalaemia can include ?
- rhabdomyolysis
- insulin deficiency
- metabolic acidosis
- hypoaldosteronism
- ACE inhibitors
- pseudohypoaldosteronism
Why could rhabdomyolysis cause hyperkalaemia ?
Hypoaldosteronism can cause hyperkalaemia as a result of what ? why ?
potassium-sparing diuretics …
Can you think why ACE inhibitors could cause hyperkalaemia ?
Why can pseudohypoaldosteronism cause hyperkalaemia ?
an inactivating mutation in ENaC channels
clinical features of hypokalaemia
clinical features of hyperkalaemia
