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Digestion and Excretion > Potassium homeostasis: renal contribution > Flashcards

Potassium homeostasis: renal contribution Flashcards

1
Q

How is the large K+ difference across cell membrane maintained?

A

Operation of Na+K+ATPase transporter

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2
Q

What 3 cell functions is K+ critical for?

A

Regulation of cell volume
Regulation of intracellular pH
Maintaining potential difference across cell membrane

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3
Q

What 4 things alter plasma K+?

A

Food intake
Acid-Base balance
Plasma osmolality
Cell lysis and excercise

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4
Q

What is the initial buffer of extracellular K+ concentration?

A

Movement of K+ into or out of skeletal muscle

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5
Q

What is the internal K+ balance?

A

Regulation of K+ distribution between intracellular and extracellular space

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6
Q

What are the most important factors regulating K+ movement under normal conditions?

A

Catecholamines (epinephrine), insulin and aldosterone

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7
Q

What is the primary mechanism to prevent a rise of K+?

A

Uptake of K+ into the cells

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8
Q

What increases uptake of K+?

A

Epinephrine, insulin and aldosterone

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9
Q

How is K+ uptake achieved?

A

Stimulation of Na+K+ATPase, 1Na+-1K+-2CL- symporter and Na+Cl symporter

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10
Q

What is insulin produced by?

A

Beta cells of pancreas

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11
Q

What is epinephrine secreted by?

A

Adrenal medulla - activates adrenergic receptors

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12
Q

What is aldosterone synthesised by?

A

Glomerulosa cells of adrenal cortex

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13
Q

What determines total K+ body content?

A

Kidneys

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14
Q

Where is K+ secreted into in the nephron?

A

Principal cells of: Late DT
CCD

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15
Q

Where is K+ mainly absorbed?

A

PT and TAL

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16
Q

What is K+ reabsorption in the PCT primarily due to?

A

Paracellular movement via solvent drag
Shift in transepithelial voltage from -ve to +ve

17
Q

What is reabsorption of K+ in TAL mainly due to?

A

Transcellular movement by NKCC2
Paracellular movement due to lumen positive voltage generated by K+ channels

18
Q

What is DCT2 the beginning of?

A

Aldosterone sensitive distal nephron and electrogenic-mediated K+ transport

19
Q

What channels are present in the DCT2?

A

ROMK channels
ENaC channels

20
Q

Where is electroneutal K+Cl- cotransport present?

A

DCT and collecting duct

21
Q

What cell surface is more permeable to K+?

A

Apical surface

22
Q

What cell is responsible for K+ secretion in initial CD and cortical CD?

A

Principal cell

23
Q

What pump is not present on basolateral side of type A intercalated cells?

A

Na+ K+ ATPase pumps

24
Q

What provides the energy for the transport function of intercalated cells?

A

H+ gradient generated by H+ATPase pumps on apical side

25
Q

When does the activity of H+K+ATPase increase?

A

In K+ depletion and acidosis

26
Q

What 3 factors influence K+ secretion by cortical collecting ducts?

A

Plasma K+
Aldosterone
ADH

27
Q

How does Plasma K+ determine K+ secretion during hyperkalemia?

A

Stimulates Na+K+ATPase -> increase K+ uptake across basolateral membrane
Increases permeability of apical membrane to K+
Increases aldosterone secretion
Increases tubular flow rate -> stimulates K+ secretion

28
Q

How does Hyperkalemia stimulate aldosterone release?

A

Causes a direct effect on cells of zona glomerulosa of adrenal cortex

29
Q

How does elevated aldosterone levels affect K+ secretion?

A

Increases Na+K+ATPase transporter expression in basolateral membrane
Increases ENaC expression in apical membrane -> increases electronegativity
Elevates SCK1 levels - further ENaC and K+ channel expression
Increases K+ channels on apical membrane

30
Q

How does ADH affect K+ secretion?

A

Increases ENaC channels on apical membrane -> increases electrochemical driving force for K+ secretion
Reduces tubular flow rate -> reduces K+ secretion
Net K+ secretion not affected

31
Q

How does a rise in tubular fluid flow affect K+ secretion?

A

Increased flow bends cillia -> cillia bend activates PKD1/PKD2 and Ca2+ entry -> imcreased Ca2+ entry actiavtes K+ channels -> K+ secretion increased

Digestion and Excretion (22 decks)

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