Potassium Balance Flashcards
What proportion of potassium is intracellular?
95%
What is the internal [K+]?
150 mmol/L
What is the external [K+]?
4.5 mmol/L
What is internal potassium balance under the influence of?
Insulin, adrenaline, pH and aldosterone
How do we get potassium into our bodies?
Diet
How do we remove potassium from our diet?
Urine, stools, sweat
What is the external potassium balance influenced by?
Intake and output
What are the two types of potassium regulation?
Acute and chronic
What does acute potassium regulation deal with?
Distribution of potassium between intra and extracellular fluid compartments (internal balance)
How is chronic potassium regulation achieved?
By the kidney adjusting potassium excretion and reabsorption (external balance)
What are the functions of potassium in the body?
Determines intracellular fluid osmolality, resting membrane potential and affects vascular resistance
What does the sodium potassium ATPase do in terms of ion concentrations?
High intracellular [K+] and low intracellular [Na+]
What is the threshold for hyperkalaemia?
Plasma [K+]> 5.5mm
What is the threshold for hypokalaemia?
Plasma [K+]<3.5mm
What is the definition of a resting membrane potential?
Membrane potential formed by creation of ionic gradients (combination of electrical and chemical gradients)
What changes to an ECG do you see in hypokalaemia?
Decreased T wave amplitude, long Q-U interval and prolonged P wave
What changes to an ECG do you see in hyperkalaemia?
Increased QRS complex, increased T wave amplitude and eventual loss of P-wave
What happens to the resting potential at low [K+]o?
Hyperpolarisation- less excitable as further from threshold point
What happens to the resting potential at high [K+]o?
Depolarisation (closer to threshold) - more excitable
What is hypokalaemia caused by?
- extensive diuretic use
- hyperaldosteronism
- prolonged vomiting
- profuse diarrhoea
How does prolonged vomiting -> hypokalaemia?
Sodium loss -> inc aldosterone secretion -> potassium excretion in kidneys
What does hypokalaemia result in?
Decreased resting membrane potential and a decreased release of adrenaline, aldosterone and insulin
When is acute hyperkalaemia normal?
Prolonged exercise
What can cause hyperkalaemia?
- insufficient renal excretion
- increased release from damaged body cells
- long term use of potassium sparing diuretics
- Addison’s disease
What types of damaged cells release potassium?
Chemo, long lasting hunger, prolonged exercise or severe burns
What happens if plasma [K+] >7mm?
Life threatening as leads to systolic cardiac arrest
What mechanisms are used to drive potassium back into cells?
Insulin/ glucose infusion and aldosterone and adrenaline stimulate the sodium potassium pump
How can CVD treatments lead to hyperkalaemia?
Beta blockers and ACE inhibitors increase serum potassium levels
Loop diuretics result in net potassium loss
How does potassium concentration change in the proximal convoluted tubule?
Potassium ions are reabsorbed passively between cells
How is potassium reabsorbed in the loop of henle?
SGLT2 transporters transport sodium, chloride and potassium
What determines potassium secretion in the distal convoluted tubule?
Increased potassium intake, changes in blood pH
How does increased plasma [K+] increase potassium secretion?
- Slows exit from basolateral membrane
- Increased activity of sodium potassium ATPase
- stimulates aldosterone secretion
What is the major regulator of potassium balance in the body?
Aldosterone
How does aldosterone affect potassium concentration?
Increased plasma aldosterone -> cortical collecting ducts increasing potassium excretion
What does aldosterone act to do?
Increase Na+/K+ ATPase pump
Increase ENaC channels
Redistribute ENaC from intracellular localisation to membrane
Increased permeability of luminal membrane
What happens to potassium conc in alkalosis?
Sodium potassium ATPase Increased so cellular K+ conc is increased -> more K+ secretion and more sodium is taken into epithelial cells
What happens to potassium conc in acidosis?
Inhibition of sodium potassium ATPase so less potassium in and so less it secreted
What is an increased flow rate in the nephron caused by?
Increased GFR, inhibition of reabsorption or potassium wasting diuretics
What happens to potassium concentration when ADH increases?
Increased potassium channel activity so increased secretion and therefore decreased cellular potassium concentration
Where is potassium reabsorbed in severe hypokalaemia?
Alpha intercalated cells or the late distal convoluted tubule is active
What effect does increased aldosterone have on potassium concentration?
Increased potassium secretion
What effect does increased sodium reabsorption have on potassium concentration?
Decreased flow rate in the tubules so less potassium secretion so increased potassium concentration
