Potassium balance Flashcards
K+ intake ?
50-100mmol/day
Output of K+?
Urine (45-112mmol)
Stools (5-10mmol)
Sweat(5mmol) (Increased loss under certain conditions)
Acute regulation?
- Distribution of K+ between intra and extra cellular fluid compartments (largely internal K+ balance)
Chronic regulation
- Achieved by the kidney readjsusting K+ excretion and reabsorption (largely “output part” of external K+ balance
K+ functions
- Determines intracellular fluid osmolality (cell volume)
- Determines resting membrane potential (important for normal functioning of excitable cells) -> repolarisation of myoctytes,cardiomyocytes and neurons
- Affects vascular resistance
How is difference in intra/extra cellular compartments maintained?
Na/K pump
Na pumped out of cell/ K pumped in
% of K+ intra/extra celluar?
> 95% intracellular
2.5% extracellular
Clincal ranges for potassium concentrations ?
Hyperkalaemia = plasma(K+)>5.5mM
Hypokalaemia = plasma (K+) <3.5mM
Which ion has a higher intracellular concentration Na+ or K+
High intracellular K+
Low intracellular Na+
Causes of hypokalaemia:
- Renal or extra renal loss of K+
- restricted intake
- Long standing use of diuretics w/out KCL compensation
- Hyperaldosteronism/Conn’s sydrome
- Prolonged vommiting ( increased Na+ loss= increasd aldosterone secretions= increased K+ excretion in kidneys)
- Crazy amounts of diarrhoea
What does hypokalaemia cause?
- Decrease in RMP
- Decrease of adrenaline/aldosterone/insulin
Where is 60-70% of the Na/K reabsorbed
Proximal convoluted tubule
Causes of hyperkalaemia?
- Acute hyperkalaemia is normal during prolonged exercise
- Disease state (decreased renal excretion)
- Increased release from damaged body cells( chemo/hunger/burns)
- long term use of K+ sparing diuretics
- Addison’s disease(adrenal insufficiency)
Aldoesterone is the major _______ of ________ balance in the body
regulator / potassium
What is ENac inhibited by?
Certain K-sparing diuretics
e.g Amiloride spironolactone
What does hyperkalaemia cause? + how is it treated?
asystolic cardiac arrest
Insulin/glucose infusion used to drive K+ into cells
How is this achieved? (K+ excretion into urine)
- activity of NA/K ATPase pump
- electrochemical gradient
- permeability of luminal membrane chanel
Sectretion of K+ into urine controlled by ???
principal cells of late DCT + CD
ENtry of Na+ (via ENac) changes electrochemical gtradient so that K+ will pass intracellular cytoplasm of principal cells and enter fluid int the tubules
blood- principal cells-fluid in CD
Conn’s syndrome
aldosterone priducing adenoma
Hyperaldosteronism
Aldosterone released in absence of stimulation by angiotensin II
↑
WHat increases K+ secretion in DCT ?
- Increased K+ intake
- Chages in blood pH
- Alkalosis= Increased excretion of K+ = decrease
serum K+ - Acute acidosis = decreased excretion of K+ = Increased serum K+
How does aldosterone regulate potassium levels ?
↑ potassium intake
↑ plasma potassium
Adrenal cortex ↑ aldosterone secretion
↑ plasma aldosterone
Cortical collecting ducts ↑ potassium secretion therefore excretion
Addison’s disease
- primary adrenal insuffiency
- damage to cortex - decrease hormone production
- deficiency in aldosterone - body secreting large amounts of Na so low serum levels- body retains K
What are the 4 ways aldosterone acts?
- ↑ activity of Na/K pump
- ↑ ENaC channels
- Redistribute ENac from intracellular localisation to membrane
- ↑ permeability of luminal membrane to K+
Plasma K+ increases K+ secretion in what ways?
- Slows exit from basolateral membrane (high k concentration inhibits channels within basolateral membrane that allow K+ into ECF)
- ↑ activity of Na/K ATPase
- Stimulates aldosterone secretion
