Potassium Homeostasis

Question 1

What is the potassium concentration inside the cell

Answer 1

150mmol/L

Question 2

What is the concentration of potassium outside the cell

Answer 2

4.5mmol/L

Question 3

What maintains the balance between the potassium concentration inside and outside the cell

Answer 3

• insulin
  -adrenaline
  -pH
  -aldosterone

Question 4

What is the intake and output of potassium

Answer 4

Intake - diet 50-100mmol/day

Output- urine 45-112 mmol/day

Question 5

What does acute regulation of potassium ions mean

Answer 5

-distribution of potassium ions between intracellular and extracellukar fluid compartments

Question 6

What is chronic potassium regulation

Answer 6

Kidney adjusting potassium ions excretion and reabsorption

Question 7

Potassium functions

Answer 7

-determines intracellular fluid osmolality
-determines resting potential membrane
-affects vascular resistance

Question 8

What maintains the big difference in concentration of potassium intracellularly and extracellularly

Answer 8

-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

Question 9

What is hyperkalaemia

Answer 9

Excess amount of plasma potassium concentration above 5.5 mM

Question 10

What is hypokalaemia

Answer 10

Plasma potassium concentration less than 3.5mM

Question 11

What happens when the plasma potassium concentration is above or below normal

Answer 11

-severely affect cardiomyocyte membrane potential , producing characteristic changes in ecg

Question 12

What are the ecg changes when someone has hypokalaemia

Answer 12

Reduced amplitude of T wave
Prolong Q U interval
Prolong p wave

Question 13

What are the ecg changes when someone has hyperkalaemia

Answer 13

Increased QRS complex
Increased amplitude of t wave
Eventual loss of p wave

Question 14

What causes hypokalaemia

Answer 14

-extra renal loss of potassium ions or restricted intake eg
-long standing use of diuretics without KCl compensation
-conns syndrome
-prolonged vomiting
-profuse diarrhoea

Question 15

What does hypokalaemia result in

Answer 15

• reduced resting potential membrane
  -reduced release of aldosterone , adrenaline , insulin

Question 16

What causes hyperkalaemia

Answer 16

-insufficient renal excretion
-increased release from damaged body cells eg chemotherapy , long lasting hunger
Long term use of potassium sparing diuretics
-addisons disease

Question 17

What causes asystolic cardiac arrest

Answer 17

-plasma potassium concentration more than 7mM

Question 18

Where is sodium and potassium reabsorbed

Answer 18

60-70% reabsorbed in proximal convoluted tubule

Question 19

What determines potassium excretion into urine in distal convoluted tubule

Answer 19

Increased potassium intake
Changes in blood pH

Question 20

What are the three ways plasma potassium concentration increases potassium ion secretion

Answer 20

-slows exit from basolateral membrane
-increased activity of Na/K ATPase , increased potassium ion concentration
-stimulates aldosterone secretion

Question 21

How is aldosterone involved in potassium secretion

Answer 21

-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

Question 22

Aldosterone mechanism of action

Answer 22

-increases activity sodium potassium pump
-increases ENAC channels
-redistributes eNaC from intracellular localization to membrane
-increases permeability of luminal membrane to potassium ions

Question 23

What other factors influence potassium secretion

Answer 23

-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

Question 24

What does the adrenal cortex produce

Answer 24

• glucocorticoids
  -sex hormones ( androgens , estrogens )
  -mineralocorticoids ( aldosterone )

Question 25

Addisons disease

Answer 25

• caused by damage to cortex
• results in lack of aldosterone production
• primary aldosterone insufficiency
  Treatment is corticosteroid

Question 26

What does a deficiency in aldosterone lead to

Answer 26

• body secreting large amounts of sodium
  -low serum sodium levels

Question 27

Conns syndrome

Answer 27

• caused by aldosterone producing adenoma of adrenal gland
  Hyperaldosteronism
  -aldosterone release in absence of stimulation of angiotensin 2

Question 28

What is the result in having conns syndrome

Answer 28

• increase in plasma aldosterone
  -kidneys to stimulate
  -develop hypertension
  -increase in fluid volume
  -leads to hyperkalaemia, hypernatremia and alkalosis

Question 29

Treatment of conns syndrome ?

Answer 29

• surgical removal of tumour containing adrenal gland
  -hypertension and hyperkalaemia controlled with potassium sparing agents