Potassium Balance Flashcards
Where is potassium typically found?
in Leafy vegetables and most fruit and fruit juice and baked or fried potatoes
What does the regulation of potassium imply?
Acute regulation- Distribution of K+ through ICF and ECF compartments
Chronic regulation: Achieved by the kidney adjusting K+ excretion & reabsorption
What is the function of Potassium?
- Determines ICF osmolality - Cell volume
- Determines resting membrane potential (RMP) -very important for normal functioning of excitable cells
- Repolarisation of cell - Myocardial, skeletal muscle & nerve cells - Affectsvascular resistance
How much potassium is found in the ECF?
2.5%
How much potassium is found intracellularly?
90%
Why is the Na+-K+ pump important?
High intracellular [K+] and low [K+]
What should the plasma concentration of K+ not exceed?
6.5mmol
Hypokalaemia
<3.5 mM
Hyperkalaemia
> 5.5 mM
How does changing K affect membrane potential?
Normal- [K] = 3.5mM and [K]i = 140mM = Ek = -98.5
Hyperkalemia- [K] = 7mM and [K]i = 140mM =Ek =-80
Hypokalemia -[K]0 = 1.5 mM and [K]i=140 mM= Ek=-121.5
Hypokalaemia and ECG
The decrease in Amplitude T-Wave, Polong Q- U interval, prolong P-wave
Hyperkalaemia and ECG
Increase QRS complex, increase amplitude T-wave, eventual loss P-wave
Hypokalaemia
Caused by renal loss of K+
- Profuse diarrhea
- Prolonged vomiting
Results: A decrease release of adrenaline, aldosterone & insulin
Hyperkalaemia
Caused by normal prolonged exercise - normal kidneys excrete K+ easily.
Or insufficient renal excretion increased release from the damaged body cells, ADDISON’S disease, and Long term use of K-sparing diuretics.
Results: Plasma [K+] >7mM life-threatining -> asystolic cardiac arrest
What hormones are needed for Hyperkalaemia?
Aldosterone, adrenaline stimulates Na+-K+ pump - increase cellular K+ influx
Renal handling Na+/K+
Human kidneys designed to conserve Na & excrete K
Na+ & K+ filtered freely at glomeruli
Plasma & GF have same [Na+] & [K+]
In 24 hrs, entire glomerular filtrate (~180 litres) contains: 25 moles Na+ (=1.5 kg NaCl)
0.7 moles K+ (=50g KCl)
K+ excretion into Urine in DCT
Increased K+ intake
Changes in blood pH
-Alkalosis = increase excretion of K+ = decrease serum [K+]
-Acute acidosis = decrease in excretion of K+ = Increase [K+]
Aldosterone & K+ secretion
The decrease in the activity of Na+/K+ pump - increase K+ influx - increase [K+] intracellular - cell lumen concentration gradient
Increase ENaC channels - increase Na+ reabsorption - decrease cell negativity and increase lumen negativity - voltage gradient
Redistributes ENaC from intracellular localization to membrane
Increase permeability of the luminal membrane to K+
How does plasma [K] increases K secretion?
In 3 ways:
-slow exit from basolateral membrane - increase [K+] intracellular - cell lumen concentration gradient
Decrease activity of Na+/K+ ATPase - increase [K+] within the cell
Increase plasma [K] - stimulates aldosterone secretion
Secondary adrenal insufficiency
- A decrease in pituitary ACTH leads to
- A decrease in cortisol
- Adrenal glands shrink
What is Conn’s syndrome?
Primary Aldosteronism
- Due to aldosterone-producing adenoma of ZG adrenal
- Usually <3cm, unilateral & renin-unresponsive
- Hyperaldosteronism (excess release of aldosterone) due to various chronic - most common (50-60%) due to Conn’s syndrome, remaining 40-50% due to bilateral adrenal hyperplasia
- Aldosterone release in absence of stimulation by Angiotensin 2
Treatment of Conn’s syndrome
Surgical removal of the tumor-containing adrenal gland
-Hypertension &hypokalaemia controlled with K+ - sparing agents e.g. spironolactone
