K+ Balance

Question 1

Plasma K concentration is a function of what?

Answer 1

Internal and external K balance

Question 2

Chronic changes in K concentration due to?

Answer 2

External balance issues

Question 3

Acute changes in K concentration due to?

Answer 3

Could be both internal or external

Question 4

How does the body handle acute K load?

Answer 4

Increase in cellular k uptake and enhanced renal k excretion
-About 75% is taken up into the cells followed by a relatively rapid excretion of K

Question 5

Can urinary excretion exceed the filtered load of k?

Answer 5

Yes, due to tubular secretion

Question 6

Primary defense against progressive K depletion and hypokalemia?

Answer 6

Renal K reabs. This is slow and can take days to develop so a substantial K deficit can occur in the meantime (unlike Na)

Question 7

What is the major regulator of internal K balance?

Answer 7

Na-K ATPase

Question 8

What factors affect internal K balance?

Answer 8

• Plasma K concentration

- Hormones (insulin, catecholamines, aldosterone)

Question 9

What factors stimulate Na-K-APTase activity?

Answer 9

• High plasma [K]
• Acute increase in plasma K stimulates insulin, aldosterone and catecholamine release which all favor K cellular uptake (also have passive diffusion into the cells)

Question 10

Catecholamines effects on K

Answer 10

-Stimulate insulin
-Work on beta 2 to increase Na-K ATPase activity and lower plasma K concentration
-

Question 11

Aldosterone effects on K

Answer 11

Stimulates Na-K ATPase activity and distal nephron K secretion and urinary excretion of K

Question 12

Effect of exercise on plasma K

Answer 12

Increase

Question 13

Effect of cell lysis on plasma k

Answer 13

Increase

Question 14

Effect of alkalemia on plasma k

Answer 14

K+ enters the cell –exchanges with H+

Question 15

Effect of acidemia on plasma K

Answer 15

K+ leaves the cell–exchanges with H+

Question 16

Effect of intracellular acidosis on plasma K

Answer 16

• Decreased intracellular pH inhibits K+ uptake, lowering intracellular K
• This displaces K+ for exit from the cell (ie increase in K+ out of the cell)

Acidosis inhibits Na-K pump and N2CCK

Question 17

Effect of plasma tonicity on plasma K

Answer 17

Hypertonic plasma: K+ follows water via drag and K passively leaks out due to cell shrinkage

-glucose increases hypertonicity in diabetic patients causing K+ plasma to increase. In non diabetics, insulin causes uptake of K+ into cells (follows water and stim Na-K)

Question 18

How would you describe the filtration of k

Answer 18

it is freely filtered
-fractional abs of 80% in the PT and 10% in the TAL is constant regardless of K balance so reabs at these sites is not a major determinant of final renal k excretion

Question 19

How much of filtered K is delivered to distal nephron?

Answer 19

About 10%

Question 20

How is K reabs in the PT?

Answer 20

Through paracellular pathways in response to Na reabs-induced fluid movement

Late PT: positive transepithelial potential difference also drives this

Luminal K channels are only minimally conductive in the PT

Question 21

How is K reabs in the Thin descending limb?

Answer 21

-Deep juxtamedullary nephrons in the medulla passively secrete K into the lumen from the interstitium

Question 22

How is K reabs in the Thin ascending limb?

Answer 22

K passively moves from cell to interstitium

Question 23

How is K reabs in the TAL?

Answer 23

• Passively due to luminal potential difference

- Actively with NKCC2 with ROMK recycling or BLM diffusion

Question 24

Alpha intercalated cells of the cortical collecting duct and outer medullary collecting duct?

Answer 24

Reabs K

• Make up <30% of cells here
• H-K ATPase actively reabs K across apical membrane and basolateral K channel for K efflux from the cell

Question 25

Principal cells of the cortical collecting duct and outer medullary collecting duct?

Answer 25

Secrete K

• make up >70% of cells here
• Apical K channels and Cl-K co transporter
• Negative potential difference in this region favors Na reabs and tehrefore K transport

Question 26

Factors affecting distal nephron K secretion

Answer 26

• K intake and plasma K concentration
• Aldosterone
• Distal tubule Na delivery and flow
• Anions in tubular fluid

Question 27

Aldosterone effect on K

Answer 27

Stimulates principal cell transport processes

-note glucocorticoids dont directly affect renal K secretion