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