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Flashcards in Potassium Control Deck (32):
1

What is the approximate ICF conc for K+?

120-150 mmol/L

2

What is the approx ECF conc of K+?

3.5 - 5 mmol/L

3

Why is it critical to maintain the ECF K+ concentration?

Effects the RMP
Effects the excitability of cardiac tissue - risk of life threatening arrhythmias with hyper- or hypokalaemias

4

Give some examples of potassium rich food

Banana
Honey dew melon
Raisins
Orange
Tomato
Baked potatoes

5

What events occur regarding K+ following a meal?

Intestine and colon absorb dietary K+
Potassium conc can rise to a dangerous ECF level
But 4/5 moves into cells within minutes
After a slight delay, kidneys begin to excrete K+
Excretion complete in 6-12 hours

6

Describe how cells and ECF balance K+

Movement K+ from ECF into cells via Na/K/ATPase
Movement K+ out of cells via K+ channels

7

What factors increase K+ uptake into cells?

Hormones - insulin, aldosterone, catecholamines
Increased potassium in ECF (concentration gradient)
Alkalosis (shift of H+ out, K+ in)

8

Give some factors promoting K+ shift out of cells

Exercise
Cell lysis
Increase ECF osmolarity (Na+ in, K+ out)
Low conc K+ in ECF (conc gradient)
Acidosis (H+ into cells, K+ out)

9

How does K+ affect insulin and vice versa?

K+ in splanchnic blood stimulates insulin secretion by pancreas
Insulin increases Na/K/ATPase activity
Increases K+ uptake into cells

10

How do aldosterone and K+ affect each other?

K+ in blood stimulates aldosterone secretion
Stimulates uptake of K+ via Na/K/ATPase

11

How do catecholamines affect K+ uptake?

Act via beta 2 adrenoceptors
Stimulate Na/K/ATPase
Increases cellular uptake of K+

12

Describe the K+ changes during exercise

Net release of K+ during the recovery phase of an action potential
K+ exits cells
Skeletal muscle damage will release K+
Plasma K+ conc proportional to the intensity of exercise

13

How is dangerous hyperkalaemia prevented in exercise?

Uptake of K+ by non-contraction tissue
Increase catecholamines to increase K+ uptake into other cells

14

In terms of K+, acidosis leads to ...

Hyperkalaemia

15

In terms of K+, alkalosis leads to...

Hypokalaemia

16

Where and how in the nephron is K+ reabsorbed?

PCT - passive, paracellular
TAL - active, NKCC2
DCT/CD - intercalated cells

17

Which cells secrete K+ into the nephron lumen?

Principal cells of DCT and cortical collecting duct

18

How does aldosterone promote K+ secretion in the kidney?

Increases transcription of the relevant proteins
Na/K/ATPase
K+ channels
ENaC

19

Why does acidic filtrate decrease K+ secretion?

Inhibits pump
Decreases K+ channel permeability

20

Why does alkalotic filtrate increase K+ secretion?

Stimulates pump
Increases K+ channel permeability

21

How is K+ reabsorbed by intercalated cells?

Active process
H/K/ATPase in apical membrane

22

What can be affected by changes in neuromuscular excitability?

Cardiac conduction
Pacemaker automaticity
Neuronal function
Skeletal muscle function
Smooth muscle function

23

Give some causes of hyperkalaemia

Increases dietary intake (unlikely)
Inappropriate dose of IV K+ (dangerous)
Decreased renal excretion - AKI/CKI, ACEi, K+ sparing diuretics, low aldosterone
Internal shifts - DKA, cell lysis, acidosis, exercise

24

Describe the effects of hyperkalaemia

Altered excitability - depolarised cardiac tissue
More Na+ channels inactivated
Heart is less excitable
Arrythmias and heart block

25

What can happen to the GI tract in hyperkalaemia?

Paralytic ileus

26

What can occur on an ECG due to hyperkalaemia?

Tented T waves
Prolonged PR interval
ST depression
No P wave
Ventricular fibrillation

27

Describe the emergency treatment for hyperkalaemia

IV calcium gluconate (reduce effect on heart)
IV insulin and dextrose (K+ into cells)
Nebuliser beta agonists
(Dialysis to remove excess K+)

28

What is the long term treatment for hyperkalaemia?

Treat the cause
Reduce K+ intake
Measure to remove excess K+ (dialysis, K+ binding resins)

29

Give some causes of hypokalaemia

Diarrhoea, vomiting
Renal loss - diuretics, increased aldosterone
Metabolic alkalosis

30

Describe what happens to the heart in hypokalaemia

Hyperpolarised RMP
More Na+ channels in the active
Heart becomes more excitable
Arrhythmias

31

What are the ECG changes in hypokalaemia?

Low T wave
High U wave
Low ST segment

32

What is the treatment for hypokalaemia?

Treat the cause
K+ replacement (IV/oral)
(K+ sparing diuretics)