10 - Regulation of Potassium Flashcards
What is Bartter’s syndrome?
- Inherited
- Thick ascending limb the NKCC2 is inhibited so low serum K+, increased blood pH, normal-low B.P, hypercalcuria so chance of stones
- Sensorineural hearing loss as this transporter also in ear
- Fluid replacement with electrolytes
What are normal potassium levels in the body?
Intracellular 140 mmol/L
Serum 3.5-5.5 mmol/L
Needed in ICF to maintain cell volume, regulate pH, control cell enzyme function, DNA and protein synthesis and cell growth
What can happen is potassium levels are too high or too low?
- Cardiac arrhytmias and arrest
- Nerve dysfunction so muscle weakness and cramps
- Constipation
- Low ECF: inability of kidneys to form concentrated urine, metabolic alkalosis, enhancement of renal ammonium excretion
What are some sources of potassium in our diets?
- Banana
- Coconut
- Tomatoes
- Potato
Where in the nephron is potassium reabsorbed and secreted?
- Majority in PCT paracellularly and K/Cl transporter
- 20-25% in thick ascending limb via NKCC2
- In DCT transport with calcium and magnesium
- In CD secretion with H+ under influence of aldosterone
What are some causes of hyperkalaemia?
How can we treat hyperkalaemia?
Need to enhance Na/K ATPase pump
What is hypokalaemia caused by?
- Vomiting
- Magnesium deficiency
- Primary and Secondary hyperaldosteronism
- Increased urine flow
How can we treat hypokalaemia?
Why do we often have to administer a mixture of two diuretics?
Diuretics tend to only work on one portion of the nephron and the nephron can compensate for the altered sodium reabsorption at different segments so blocking two segments increases drug efficacy
What is the only diuretic that works on the PCT and what is it now used for instead of a diuretic and why?
- Carbonic anhydrase inhibitors, e.g acetazolamide, stop NaHCO3 reabsorption rather than NaCl
- Not that effective as less sodium bicarbonate than NaCl and this was leading to metabolic acidosis
- Used for glaucoma to reduce formation of aqueous humour and infantile epilepsy
What are some different classes of diuretics, where do they work in the nephron and what are some examples of each class?
What happens to serum potassium during intense exercise?
Increases
Where does excretion of potassium from the body occur?
- 80% kidney
- 20% faeces and sweat
GFR = 125ML/MIN
Serum K+ = 4
Total removal a day = 800mmol/L
What factors increase Na/K ATPase activity?
- K+ concentration in plasma
- Insulin
- Noradrenaline effect on B2 adrenoreceptors
What factors can affect K+ secretion in the collecting duct?
What is Liddle’s syndrome?
- Autosomal dominant disease that causes increased activity of ENaC in the collecting duct
- Increased excretion of K but overabsorption of Na and H2O
- High B.P, low blood K+, metabolic alkalosis, lowered renin and aldosterone
What is the urinary and vascular pole in the nephron?
- Vascular pole is where arterioles enter and leave the Bowman’s capsule
- Urinary pole is where PCT starts
A woman presents with hyperparathyroidism, what effect will this have on her phosphate levels in the blood and why?
Increased excretion of phosphate in the urine as PTH inhibits Na/Pi channel in the PCT so more phopshate in the urine
A young girl presents with an eating disorder where she has been making herself vomit, she has hypokalaemia, why is this?
Increased kidney tubular potassium secretion due to the loss of H+ in the vomit so metabolic alkalosis. Losing potassium to correct acid base status
