Potassium

Question 1

What is normal serum potassium?

Answer 1

3.5-5.3mmol/L

Question 2

How is serum potassium different to plasma potassium?

Answer 2

plasma K+ is usually 2-3mmol/L lower

Question 3

How is potassium lost from he body?

Answer 3

majority through the kidney

- small amount through colon and skin

Question 4

What is the major sites of potassium resorption?

Answer 4

• proximal tubule
• loop of Henle 20-30% K+ is resorbed
• the remaining 10% is taken up in the distal tubule due to the fine tubing coordinated by aldosterone

Question 5

Homeostasis of K+ in health is regulated by:
- 
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-
-

Answer 5

hormones
acid-base balance
plasma tonicity
plasma [K+]

Question 6

What 3 substances are released if plasma K+ goes up?

What are their effects?

Answer 6

insulin –> uptake into cells
aldosterone –> increase renal excretion
catecholamine –> uptake into cells

Question 7

How does RAAS alter K+?

Answer 7

• Renin is secreted in hypotension
• aldosterone is produced
• this leads to K+ exchange for Na+ and H+
• this causes a net decrease in K+ and increase in Na+

Question 8

There can be an increase in the activity of RAAS in 
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-
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This will lead to...

Answer 8

• Conn’s syndrome
• Cushing’s syndrome
• renal artery stenosis

Decrease K+

Question 9

How does Cushing’s cause deceased potassium?

Answer 9

• cortisol acts as a partial against at the aldosterone receptor
• cortisol is the main hormone that causes Na+ uptake and K+ loss
• as the levels of cortisol are considerably higher than aldosterone levels (aldosterone is just fine tuning)

Question 10

What is Conn’s syndrome?

Answer 10

solitary aldosterone producing adenoma

–> hypertension, hypernatraemia, hypokalaemia, alkalosis

Question 11

What are the causes of an underactive RAAS?

How does this affect K+?

Answer 11

adrenal insufficiency
ACE inhibition
dosing with spironolactone
- increases K+

Question 12

How can an underactice RAS be diagnosed?

Answer 12

short synacthen test

- will cause no response

Question 13

How is K+ affected in metabolic acidosis?

Answer 13

• inhibition of tubular K- secretion as Na/H exchange occurs preferentially to Na/K exchange, hence there is increased K+ level.
  This process also happens outside of the kidney, as K+ will move from the intracellular to the extracellular space in exchange for H+

Question 14

What happens in metabolic alkalosis?

Answer 14

• H will move into extracellular fluid, hence to preserve neutrality K+ moves into the cell and is lost in the urine