Potassium Balance

Question 1

Where is potassium typically found?

Answer 1

in Leafy vegetables and most fruit and fruit juice and baked or fried potatoes

Question 2

What does the regulation of potassium imply?

Answer 2

Acute regulation- Distribution of K+ through ICF and ECF compartments

Chronic regulation: Achieved by the kidney adjusting K+ excretion & reabsorption

Question 3

What is the function of Potassium?

Answer 3

1. Determines ICF osmolality - Cell volume
2. Determines resting membrane potential (RMP) -very important for normal functioning of excitable cells
   - Repolarisation of cell - Myocardial, skeletal muscle & nerve cells
3. Affectsvascular resistance

Question 4

How much potassium is found in the ECF?

Answer 4

2.5%

Question 5

How much potassium is found intracellularly?

Answer 5

90%

Question 6

Why is the Na+-K+ pump important?

Answer 6

High intracellular [K+] and low [K+]

Question 7

What should the plasma concentration of K+ not exceed?

Answer 7

6.5mmol

Question 8

Hypokalaemia

Answer 8

<3.5 mM

Question 9

Hyperkalaemia

Answer 9

> 5.5 mM

Question 10

How does changing K affect membrane potential?

Answer 10

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

Question 11

Hypokalaemia and ECG

Answer 11

The decrease in Amplitude T-Wave, Polong Q- U interval, prolong P-wave

Question 12

Hyperkalaemia and ECG

Answer 12

Increase QRS complex, increase amplitude T-wave, eventual loss P-wave

Question 13

Hypokalaemia

Answer 13

Caused by renal loss of K+

• Profuse diarrhea
• Prolonged vomiting

Results: A decrease release of adrenaline, aldosterone & insulin

Question 14

Hyperkalaemia

Answer 14

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

Question 15

What hormones are needed for Hyperkalaemia?

Answer 15

Aldosterone, adrenaline stimulates Na+-K+ pump - increase cellular K+ influx

Question 16

Renal handling Na+/K+

Answer 16

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)

Question 17

K+ excretion into Urine in DCT

Answer 17

Increased K+ intake
Changes in blood pH
-Alkalosis = increase excretion of K+ = decrease serum [K+]
-Acute acidosis = decrease in excretion of K+ = Increase [K+]

Question 18

Aldosterone & K+ secretion

Answer 18

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+

Question 19

How does plasma [K] increases K secretion?

Answer 19

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

Question 20

Secondary adrenal insufficiency

Answer 20

1. A decrease in pituitary ACTH leads to
2. A decrease in cortisol
3. Adrenal glands shrink

Question 21

What is Conn’s syndrome?

Answer 21

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

Question 22

Treatment of Conn’s syndrome

Answer 22

Surgical removal of the tumor-containing adrenal gland

-Hypertension &hypokalaemia controlled with K+ - sparing agents e.g. spironolactone