ChemPath 4: Potassium and Electrolytes Flashcards
What is the Normal Value of sodium?
135-145 mmol/L
What is the Normal Value of potassium?
3.5-5.3 mmol/L
What is the Normal Value of urea?
2.5-6.7 mmol/L
What is the Normal Value of creatinine?
- 70-100 micromol/L
What is the Normal Value of Hb?
- Men: 130-180 g/L; Women: 115-160 g/L
What is the Normal Value of WBCs?
- 4-11 x109 cells/L
What is the normal value of platelets?
- 150-400 x109 cells/L
What is the most abundant intracellular cation?
Potassium
What is the most abundant extracellular cation?
Sodium
What is the Potassium plasma/serum concentration?
3.5-5.3 mmol/L
How is potassium regulated?
- Loss through the GI tract
- Renal regulation and secretion:
- Angiotensin II
- Aldosterone
- Movement from intracellular to extracellular
Which cells does aldosterone act on?
principal cells of the cortical collecting tube
Describe the renin-angiotensin-aldosterone system
- Angiotensinogen → Ang-1 [LIVER via renin from JGA]; renin release via…
- Low BP (inrenalartery)
- Low Na+ in macula dense by JGA
- SNS beta-1 receptor activation
- Ang-1 → Ang-2 [LUNGS via ACE]
- Ang-2 acts on the adrenals to release aldosterone
- Aldosterone excretes K+ and increases Na+ retention
- Trigger for aldosterone release:
- Angiotensin II
- Potassium (high)
What does aldosterone bind to?
• Aldosterone binds to MR steroid receptor…
What happens once aldosterone binds to the MR steroid receptor?
(1) ENaC creation (Na resorption)
- Na+resorption from urine occurs through ENaC (Epithelial Sodium Channels) to create a -ve electrical potential in the renal lumen
- This drives K+ secretion into renal lumen through ROMK (Renal Outer Medullary Potassium) channel
(2) ROMK creation (K excretion)
(3) Sgk1 (Serum Glucocorticoid Kinase 1)
- increased Sgk1
- → reduced Nedd4 (less phosphorylation or Nedd4)
- → reduced degradation of ENaC (sodium channels)
- → same happens as (1)
What is the overall action of aldosterone?
Aldosterone increases the number of open Na+ channels in renal luminal membrane
→ Na+ resorption from renal lumen (urine)
→ this makes the lumen electronegative and creates an electrical gradient
→ K+ is secreted into the renal lumen (urine)
What are the 2 stimuli for aldosterone secretion?
- Angiotensin II
- Potassium (high)
What are the causes of hyperkalaemia?
- reduced GFR
- reduced Renin
- T4 RTA (diabetic nephropathy)
- NSAIDs
- ACE inhibitors
- ARBs (Angiotensin 2 Receptor Blockers)
- Addison’s disease
- Aldosterone antagonists (i.e. spironolactone)
When is potassium released from cells?
-
Rhabdomyolysis
- (muscle death release K+)
-
Acidosis
- H+ taken into cells (to stabilise the disturbance) → H+/K+ transporter is disrupted → K+ is excreted in response (to maintain membrane electronegativity)
What are the MAIN causes of hyperkalaemia?
- Renal impairment – reduced renal excretion
- Drugs – ACEi, ARBs, spironolactone
- Low aldosterone
- Addison’s disease
- T4 renal tubular acidosis (low renin, low aldosterone)
- Release from cells – rhabdomyolysis, acidosis
What are the ECG changes associated with hyperkalaemia?
- Peaked T wave (early) - ‘tall, tented T waves’
- Broad QRS
- Flat P-wave
- Prolonged PR (and bradycardia)
- Sine wave (latest)
What is the management of hyperkalaemia?
- 10mL 10% Calcium Gluconate (stabilise)
- 50mL 50% Dextrose (*drive K+ into cells)
- 10U Insulin*
- Nebulised salbutamol*
- Tx underlying cause
What are the causes of hypokalaemia?
How does increased Na+ delivery to DCT *cause Osmotic diuresis?
- Triple- or co-transporter is blocked →. less Na+ is resorbed in the ascending LoH → more goes to the DCT
- Triple= (furosemide)
- Co-transporter= (bendroflumethiazide)
- More Na+ reaches and is absorbed in the DCT → a more electronegative nephron
- This results in loss of K+ down the electrochemical gradient through ROMK channels
What are the clinical features of hypokalaemia?
- Muscle weakness
- Cardiacarrhythmias (ECG = ST depression, flat T-waves, U waves)
- Polyuria and polydipsia (nephrogenic DI from low K+ or a high Ca2+)
What is the main differential you must rule out in a patient with reduced K+ and hypertension?
Conn’s syndrome