Potassium Homeostasis Flashcards
What is the potassium concentration inside the cell
150mmol/L
What is the concentration of potassium outside the cell
4.5mmol/L
What maintains the balance between the potassium concentration inside and outside the cell
- insulin
-adrenaline
-pH
-aldosterone
What is the intake and output of potassium
Intake - diet 50-100mmol/day
Output- urine 45-112 mmol/day
What does acute regulation of potassium ions mean
-distribution of potassium ions between intracellular and extracellukar fluid compartments
What is chronic potassium regulation
Kidney adjusting potassium ions excretion and reabsorption
Potassium functions
-determines intracellular fluid osmolality
-determines resting potential membrane
-affects vascular resistance
What maintains the big difference in concentration of potassium intracellularly and extracellularly
-the sodium potassium pump
- hydrolysis of atp to adp
-potassium pulled into the cells , expels sodium from cells
-maintains high intercellular potassium concentration, low sodium concentration
What is hyperkalaemia
Excess amount of plasma potassium concentration above 5.5 mM
What is hypokalaemia
Plasma potassium concentration less than 3.5mM
What happens when the plasma potassium concentration is above or below normal
-severely affect cardiomyocyte membrane potential , producing characteristic changes in ecg
What are the ecg changes when someone has hypokalaemia
Reduced amplitude of T wave
Prolong Q U interval
Prolong p wave
What are the ecg changes when someone has hyperkalaemia
Increased QRS complex
Increased amplitude of t wave
Eventual loss of p wave
What causes hypokalaemia
-extra renal loss of potassium ions or restricted intake eg
-long standing use of diuretics without KCl compensation
-conns syndrome
-prolonged vomiting
-profuse diarrhoea
What does hypokalaemia result in
- reduced resting potential membrane
-reduced release of aldosterone , adrenaline , insulin
What causes hyperkalaemia
-insufficient renal excretion
-increased release from damaged body cells eg chemotherapy , long lasting hunger
Long term use of potassium sparing diuretics
-addisons disease
What causes asystolic cardiac arrest
-plasma potassium concentration more than 7mM
Where is sodium and potassium reabsorbed
60-70% reabsorbed in proximal convoluted tubule
What determines potassium excretion into urine in distal convoluted tubule
Increased potassium intake
Changes in blood pH
What are the three ways plasma potassium concentration increases potassium ion secretion
-slows exit from basolateral membrane
-increased activity of Na/K ATPase , increased potassium ion concentration
-stimulates aldosterone secretion
How is aldosterone involved in potassium secretion
-potassium intake increases
-increases plasma potassium
-adrenal cortex increases aldosterone secretion
-increase in plasma aldosterone
-which acts on principal cells in cortical collecting duct and dct to increase potassium secretion into urine
Aldosterone mechanism of action
-increases activity sodium potassium pump
-increases ENAC channels
-redistributes eNaC from intracellular localization to membrane
-increases permeability of luminal membrane to potassium ions
What other factors influence potassium secretion
-alkalosis -
-acidosis - lowered ph inhibits sodium potassium atpase , decrease of potassium ions inside cell
-tubular flow rate, you can increase by increasing GFR
-decrease in ECFV
-renin-angiotensin 2-aldosterone
What does the adrenal cortex produce
- glucocorticoids
-sex hormones ( androgens , estrogens )
-mineralocorticoids ( aldosterone )
