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ESA 3- Urinary System > Control of Potassium Concentration > Flashcards

Control of Potassium Concentration Flashcards

1
Q

What are the most abundant intra-cellular cation?

A

K+ ions

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2
Q

What % of the total body K+ content is intracellular?

A

98%

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3
Q

What % of the total body K+ content is in the ECF?

A

2%

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4
Q

What does the body do, regarding plasma [K+]?

A

Tightly maintains it

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5
Q

Within what range does the body maintain plasma [K+]?

A

3.5-5.3mmol/L

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6
Q

Where is [K+] high?

A

Inside cells

Inside mitochondria

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7
Q

What is high [K+] inside cells and mitochondria essential for?

A 
Maintaining cell volume
Regulating intra-cellular pH 
Controlling cell-enzyme function
DNA/protein synthesis
Cell growth
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8
Q

What is low [K+] outside cells necessary for?

A

Maintaining the steep K+ ion gradient across cell membranes

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9
Q

What is the steep K+ ion gradient across cell membrane largely responsible for?

A

The membrane potential of excitable and non-excitable cells

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10
Q

What is the result of increased ECF [K+] on cell membranes?

A

Depolarises

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11
Q

What is the result of decreased ECF [K+] on cell membranes?

A

Hyperpolarises

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12
Q

What is the result of changes in extracellular [K+]?

A

Can cause severe disturbances in excitation and contraction

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13
Q

What can result from hyperkalaemia, regarding excitation and contraction?

A

Potentially life threatening disturbances of cardiac rhythm

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14
Q

What can extremely low [K+] lead to?

A

Several metabolic disturbances

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15
Q

What metabolic disturbances can extremely low [K+] lead to?

A

Inability of the kidney to form concentrated urine
A tendency to develop metabolic alkalosis
Large enhancement of renal ammonium excretion

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16
Q

What keeps ECF [K+] tightly controlled?

A

Two homeostatic mechanisms

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17
Q

What homeostatic mechanisms keep [K+] tightly controlled?

A

External and internal balance

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18
Q

What happens to K+ at the glomerulus?

A

It is filtered freely

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19
Q

In what segments of the nephron does potassium handling occur?

A

Proximal tubule
Thick ascending limb
Principal cells of DCT and cortical collecting duct
Intercalated cells of DCT and cortical collecting duct, and medually collecting duct

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20
Q

Where does the handling of K+ in the nephron differ based on the K+ content of the diet?

A

Principal cells of DCT and cortical collecting duct

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21
Q

Is K+ reabsorption in the proximal tubule passive or active?

A

Passive

22
Q

How is K+ reabsorbed in the proximal tubule?

A

Paracellular diffusion

23
Q

How much K+ is reabsorbed in the proximal tubule?

A

67%

24
Q

Is K+ reabsorption in the thick ascending limb an active or passive process?

A

Active

25
Q

What is active reabsorption of K+ in the thick ascending limb driven by?

A

Na-K-ATPase pumps in basolateral membrane

26
Q

What is required for reabsorption of K+ in the thick ascending limb?

A

Na-K-Cl transporter in the apical membrane

27
Q

How much K+ is reabsorbed in the thick ascending limb?

A

20%

28
Q

What happens in the principal cells of DCT and cortical collecting duct in a normal or high K+ diet?

A

Substantial secretion (15-20%)

29
Q

What happens in the principal cells of DCT and cortical collecting duct in a low K+ diet or depletion?

A

Little secretion

30
Q

How much K+ is reabsorbed in the intercalated cells of DCT and cortical collecting duct, and medullary collecting duct?

A

10-12%

31
Q

What cells are involved in K+ secretion in the DCT and cortical CD?

A

Principal cells

32
Q

Is secretion of K+ by principal cells an active or passive process?

A

Active

33
Q

What is the secretion of K+ by principal cells driven by?

A

Electro-chemical gradient for K+ between principal cell and lumen, set up by Na-K-ATPase

34
Q

How is the electrochemical gradient for K+ secretion produced?

A

Na+ is reabsorbed by ENaC. This creates a negative charge in the lumen, favouring K+ secretion by a separate K+ channel

35
Q

Where is the Na-K-ATPase driving secretion of K+ by principal cells found?

A

In the basolateral membrane

36
Q

Why is Na-K-ATPase required to drive secretion of K+ by principal cells?

A

It creates the gradient for Na absorption

37
Q

What are the categories of factors affecting K+ secretion by the principal cell?

A

Tubular factors

Luminal factors

38
Q

What tubular factors affect K+ secretion by the principal cell?

A

Aldosterone
ECF [K+]
Acid base status

39
Q

What luminal factors affect K+ secretion by the principal cell?

A

Increase distal tubular flow rate

Increased Na+ delivery to distal tubule

40
Q

What is aldosterone?

A

A steroid hormone

41
Q

What does aldosterone do, regarding channels?

A

Increases the transcription of Na-K-ATPase in the basolateral membrane, and ENaC/K+ channels in the apical membrane

42
Q

What is the result of the increased channel resulting from aldosterone?

A

The increased amount of these channels gives increased K+ excretion

43
Q

Does hyperkalaemia or hypokalaemia cause increased K+ sescretion?

A

Hyperkalaemia

44
Q

How does hyperkalaemia increase K+ secretion

A

It stimulates aldosterone secretion, increasing K+ secretion

45
Q

How does acid base status affect K+ secretion?

A

Changes in the ECF pH cause reciprocal shifts in H+ and K+ between ECF and ICF

46
Q

What effect does acidaemia have on K+ secretion?

A

Decreases it

47
Q

Why does acidaemia decrease K+ secretion?

A

It decreases [K+] concentration in principal cells

48
Q

What effect does alkalosis have on K+ secretion?

A

Increases it

49
Q

Why does alkalosis increase K+ secretion?

A

Increases [K+] in principal cells

50
Q

What cells are involved in K+ absorption in the DCT?

A

Intercalated cells

51
Q

Is the absorption of K+ by intercalated cells an active or passive process?

A

Active

52
Q

What is the absorption of K+ by intercalated cells mediated by?

A

H+ -K+ -ATPase in the apical membrane

ESA 3- Urinary System (13 decks)

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