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Urinary system > Control of potassium > Flashcards

Control of potassium Flashcards

1
Q

Are most potassium ions in the body intracellular or extracellular?

A

Intracellular

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2
Q

What are the concentrations of intracellular and extracellular potassium ions?

A

Intracellular - 160mmol/L

Extracellular - 5mmol/L

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3
Q

What is the main source of potassium ions?

A

Diet

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4
Q

How are most potassium ions lost from the body?

A

Urine

then faeces, sweat

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5
Q

What is responsible for matching potassium ion intake to potassium ion loss from the body?

A

Kidneys excreting it into the urine

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6
Q

What mechanisms are responsible for maintaining a constant plasma potassium ion concentration? Which is the first-line mechanism?

A

Cells taking it up or releasing it - first line mechanism

Kidneys excreting it into urine

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7
Q

How are potassium ions taken up into cells?

A

Na+ K+ ATPase on cell membranes

actively transports 2 potassium ions into cells

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8
Q

What stimulates potassium ions to be taken up into cells?

A

Extracellular potassium ion concentration

Insulin

Noradrenaline

Aldosterone

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9
Q

What receptor does noradrenaline bind to when stimulating potassium ion uptake into cells?

A

B2 adrenoceptors

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10
Q

What stimulates potassium ion release from cells?

A

Acidosis

Cell damage, death

Increased extracellular fluid osmolality

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11
Q

How does increased extracellular fluid osmolality stimulate potassium ion release from cells?

A

Water moves out of cells into the extracellular fluid
increase in intracellular potassium ion concentration
potassium ions diffuse out of the cell

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12
Q

What inhibits potassium ion release from cells?

A

Alkalosis

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13
Q

What are the proportions of filtered potassium ions reabsorbed along the nephron?

A

Proximal convoluted tubule - 67%

Loop of Henle, mostly thick ascending limb - 20%

Collecting duct - variable

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14
Q

What does the proportion of filtered potassium ions reabsorbed in the collecting duct depend on?

A

Potassium ion intake

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15
Q

How are potassium ions reabsorbed in the proximal convoluted tubule?

A

By solvent drag

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16
Q

What is solvent drag?

A

Ions and molecules being moved by the flow of water

17
Q

How are potassium ions secreted in principal cells of the collecting duct?

A

Na+ K+ ATPase on basolateral domain
actively transports 2 potassium ions from interstitial fluid into principal cell

ROMK channels and BK channels on apical domain
potassium ions move through them from the cell into the tubular lumen down their electrochemical gradient

18
Q

What stimulates potassium ion secretion from the principal cells?

A

High extracellular fluid potassium ion concentration

Aldosterone

High tubular flow rate

19
Q

How does high extracellular fluid potassium ion concentration stimulate potassium ion secretion from the principal cells?

A

Increased concentration gradient for potassium ion secretion

Stimulates aldosterone secretion

20
Q

How does aldosterone stimulate potassium ion secretion from the principal cells?

A

Increases activity of Na+ K+ ATPase on basolateral domain
more potassium ions actively transported from interstitial fluid into cell

Increased expression of ENaC on apical domain
more sodium ions move through it from tubular lumen into cell
more negatively charged lumen
more potassium ions move through ROMK and BK channels from cell into lumen down their electrochemical gradient

Increased ROMK and BK channels on apical domain

21
Q

What is the aldosterone paradox?

A

Refers to how the sodium ion reabsorption can be stimulated without increasing potassium ion secretion

And how potassium ion secretion can be stimulated without increased sodium ion reabsorption

22
Q

How can sodium ion reabsorption be stimulated without increasing potassium ion secretion in the aldosterone paradox?

A

Aldosterone increases expression of ENaC on apical domain of epithelial cells on later distal convoluted tubule and principal cells of collecting duct
more sodium ions move through it from tubular lumen into cells

Angiotensin 2 inhibits ROMK on apical domain of epithelial cells in principal cells of collecting duct
fewer potassium ions move through it from cell into lumen

23
Q

How can potassium ion secretion be stimulated without increasing sodium ion reabsorption in the aldosterone paradox?

A

High extracellular fluid potassium concentration stimulates aldosterone release
aldosterone gives increased expression of ENaC on apical domain of principal cells
more sodium ions move through it from tubular lumen into cells
more negatively charged lumen
more potassium ions move through ROMK channels on apical domain from cells into lumen down their electrical gradient

But other sodium transporters are inhibited
fewer sodium ions moved from lumen into epithelial cells

24
Q

How does a high tubular flow rate stimulate potassium ion secretion from principal cells?

A

Removes secreted potassium ions from tubular lumen
reduced concentration of potassium ions in tubular lumen
maintains concentration gradient

Increased expression of BK channels on apical domain
more potassium ions move through them from principal cell into lumen

25
Q

What inhibits potassium ion secretion from the principal cells?

A

Acidosis

26
Q

What are the signs and symptoms of hypokalaemia?

A

Weakness

Muscle weakness, muscle pain, muscle tremors

Constipation

Cardiac arrythmias

27
Q

Why does hypokalaemia cause muscle weakness, pain and tremors?

A

Disturbed function of skeletal muscle

28
Q

Why does hypokalaemia cause constipation?

A

Disturbed function of smooth muscle

29
Q

What does an ECG of a patient with hypokalaemia look like?

A

Shorter T waves

ST segment depression, T wave inversion

U wave

30
Q

What are the causes of hypokalaemia?

A

Reduced dietary intake

Increased uptake into cells - metabolic alkalosis, stress

GI loss - vomiting, diarrhoea

Urinary loss - high aldosterone, high flow

31
Q

How is hypokalaemia treated?

A

Oral potassium supplements

IV potassium

Urinary system (25 decks)

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