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Urinary System > Potassium Control > Flashcards

Potassium Control Flashcards

1
Q

What is the approximate ICF conc for K+?

A

120-150 mmol/L

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2
Q

What is the approx ECF conc of K+?

A

3.5 - 5 mmol/L

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3
Q

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

A

Effects the RMP

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

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4
Q

Give some examples of potassium rich food

A 
Banana 
Honey dew melon 
Raisins 
Orange 
Tomato
Baked potatoes
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5
Q

What events occur regarding K+ following a meal?

A

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

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6
Q

Describe how cells and ECF balance K+

A

Movement K+ from ECF into cells via Na/K/ATPase

Movement K+ out of cells via K+ channels

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7
Q

What factors increase K+ uptake into cells?

A

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

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8
Q

Give some factors promoting K+ shift out of cells

A 
Exercise
Cell lysis 
Increase ECF osmolarity (Na+ in, K+ out)
Low conc K+ in ECF (conc gradient)
Acidosis (H+ into cells, K+ out)
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9
Q

How does K+ affect insulin and vice versa?

A

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

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10
Q

How do aldosterone and K+ affect each other?

A

K+ in blood stimulates aldosterone secretion

Stimulates uptake of K+ via Na/K/ATPase

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11
Q

How do catecholamines affect K+ uptake?

A

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

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12
Q

Describe the K+ changes during exercise

A

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

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13
Q

How is dangerous hyperkalaemia prevented in exercise?

A

Uptake of K+ by non-contraction tissue

Increase catecholamines to increase K+ uptake into other cells

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14
Q

In terms of K+, acidosis leads to …

A

Hyperkalaemia

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15
Q

In terms of K+, alkalosis leads to…

A

Hypokalaemia

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16
Q

Where and how in the nephron is K+ reabsorbed?

A

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

17
Q

Which cells secrete K+ into the nephron lumen?

A

Principal cells of DCT and cortical collecting duct

18
Q

How does aldosterone promote K+ secretion in the kidney?

A

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

19
Q

Why does acidic filtrate decrease K+ secretion?

A

Inhibits pump

Decreases K+ channel permeability

20
Q

Why does alkalotic filtrate increase K+ secretion?

A

Stimulates pump

Increases K+ channel permeability

21
Q

How is K+ reabsorbed by intercalated cells?

A

Active process

H/K/ATPase in apical membrane

22
Q

What can be affected by changes in neuromuscular excitability?

A 
Cardiac conduction 
Pacemaker automaticity 
Neuronal function 
Skeletal muscle function 
Smooth muscle function
23
Q

Give some causes of hyperkalaemia

A

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
Q

Describe the effects of hyperkalaemia

A

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

25
Q

What can happen to the GI tract in hyperkalaemia?

A

Paralytic ileus

26
Q

What can occur on an ECG due to hyperkalaemia?

A 
Tented T waves
Prolonged PR interval
ST depression
No P wave
Ventricular fibrillation
27
Q

Describe the emergency treatment for hyperkalaemia

A

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

28
Q

What is the long term treatment for hyperkalaemia?

A

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

29
Q

Give some causes of hypokalaemia

A

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

30
Q

Describe what happens to the heart in hypokalaemia

A

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

31
Q

What are the ECG changes in hypokalaemia?

A

Low T wave
High U wave
Low ST segment

32
Q

What is the treatment for hypokalaemia?

A

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

Urinary System (14 decks)

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