Potassium homeostasis: renal contribution

Question 1

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

Answer 1

Operation of Na+K+ATPase transporter

Question 2

What 3 cell functions is K+ critical for?

Answer 2

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

Question 3

What 4 things alter plasma K+?

Answer 3

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

Question 4

What is the initial buffer of extracellular K+ concentration?

Answer 4

Movement of K+ into or out of skeletal muscle

Question 5

What is the internal K+ balance?

Answer 5

Regulation of K+ distribution between intracellular and extracellular space

Question 6

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

Answer 6

Catecholamines (epinephrine), insulin and aldosterone

Question 7

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

Answer 7

Uptake of K+ into the cells

Question 8

What increases uptake of K+?

Answer 8

Epinephrine, insulin and aldosterone

Question 9

How is K+ uptake achieved?

Answer 9

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

Question 10

What is insulin produced by?

Answer 10

Beta cells of pancreas

Question 11

What is epinephrine secreted by?

Answer 11

Adrenal medulla - activates adrenergic receptors

Question 12

What is aldosterone synthesised by?

Answer 12

Glomerulosa cells of adrenal cortex

Question 13

What determines total K+ body content?

Answer 13

Kidneys

Question 14

Where is K+ secreted into in the nephron?

Answer 14

Principal cells of: Late DT
CCD

Question 15

Where is K+ mainly absorbed?

Answer 15

PT and TAL

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

What is DCT2 the beginning of?

Answer 18

Aldosterone sensitive distal nephron and electrogenic-mediated K+ transport

Question 19

What channels are present in the DCT2?

Answer 19

ROMK channels
ENaC channels

Question 20

Where is electroneutal K+Cl- cotransport present?

Answer 20

DCT and collecting duct

Question 21

What cell surface is more permeable to K+?

Answer 21

Apical surface

Question 22

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

Answer 22

Principal cell

Question 23

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

Answer 23

Na+ K+ ATPase pumps

Question 24

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

Answer 24

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

Question 25

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

Answer 25

In K+ depletion and acidosis

Question 26

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

Answer 26

Plasma K+ Aldosterone ADH

Question 27

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

Answer 27

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

Question 28

How does Hyperkalemia stimulate aldosterone release?

Answer 28

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

Question 29

How does elevated aldosterone levels affect K+ secretion?

Answer 29

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

Question 30

How does ADH affect K+ secretion?

Answer 30

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

Question 31

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

Answer 31

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