L1: Disorders of Potassium Balance Flashcards
Where is potassium mainly stored?
intracellularly
After eating, what happens to the excess potassium entering your body?
cellular distribution - it is moved intracellularly
List the 5 key regulators of potassium cellular distribution - they influence the movement of K+ intracellularly?
- Insulin*
- Catecholamines*
- pH
- Cell Turnover
- Osmolality
How do catecholamines regulate potassium cellular distribution?
stimulates Na+/K+ ATPase - drives K+ into cells
How does insulin regulate potassium cellular distribution? What is the effect of insulin after eating a meal?
stimulates Na+/K+ ATPase - drives K+ into cells
after a meal: moves K+, glucose and phosphate into the cell
How does pH regulate potassium cellular distribution? What happens in low and high pH?
via H+/K+ channel
Low pH: H+ pumped into cell, K+ pumped out
High pH: H+ pumped out of cell, K+ pumped in
How does cell turnover regulate potassium cellular distribution?
- if cell breaks down, it releases K+
- in increased cell turnover, increased K+ intracellularly
How does osmolality affect potassium cellular distribution?
- if hypertonic outside cell, water drawn out
- water draws K+ out of cell with it
Result: low intracellular K+, high plasma K+ (hyperkalaemia)
What are 2 mechanisms by which potassium is regulated through in the body?
- Cellular Distribution
2. Renal Excretion
Where is potassium reabsorbed and excreted in the nephron?
K+ reabsorbed in proximal tubule + loop of Henle
K+ excreted in cortical collecting duct
What are the 2 main principal cell types of the cortical collecting duct? What are the functions of each?
- Principal Cells - K+ excretion
2. Intercalated Cells - H+ excretion
Generally explain what occurs for K+ excretion in the cortical collecting duct.
- Na+ reabsorbed by ENaC channels
- Na+ pumped out of principal cell by Na+/K+ channel
- Cl- creates negative charge in tubular lumen
- K+ excreted into tubule
What are ENaC channels?
they are epithelial Na+ channels located in the cortical collecting duct
Potassium excretion in the principal cells of the collecting duct is regulated by what 2 processes?
- Tubular Flow
2. Aldosterone
What is defined as hypokalaemia? What is moderate hypokalaemia? What is severe hypokalaemia?
Hypokalaemia = < 3.5 mmol/L
Moderate Hypokalaemia = < 3.0 mmol/L
Severe Hypokalaemia = < 2.5 mmol/L
List 3 major causes of hypokalaemia
- Decreased Intake
- Intracellular Shift
- Increased Renal Excretion
How can refeeding syndrome cause hypokalaemia?
there is insulin release which will draw K+ into cells
What is primary hyperaldosteronism? What is another name for it?
aka Conn’s Syndrome
when adrenal glands produce too much aldosterone
What is secondary hyperaldosteronism?
increase in aldosterone as a consequence of something else (e.g. diuretics, vomiting - loss of volume)
Explain diuretic-induced hypokalaemia
- diuretics inhibit Na+ reabsorption
- increased Na+ (and water) in urine
- increased urine output; decrease blood volume
- aldosterone stimulated due to decrease blood volume (pressure0
- aldosterone increases Na+ reabsorption and K+ excretion
Explain vomit-induced hypokalaemia
- vomit contains acid (increased excretion of acid)
- leads to metabolic alkalosis
- increase HCO3- in tubule
- HCO3- creates a strong negative gradient
- draws K+ into the tubule
aldosterone also stimulated (due to volume loss)
- causes Na+ reabsorption and K+ excretion
List some of the consequences of hypokalaemia
- muscle weakness/paralysis
- ECG changes and arrhythmia
- urinary concentrating deficits
- hypertension and stroke
On an ECG of a patient with hypokalaemia, what can be seen?
inverted T/U waves
What is the preferred treatment for hypokalaemia
potassium (oral preferred over IV)
