Lecture 20 - Renal Regulation of Ion Concentrations

Question 1

Describe the distribution of potassium ions in the body.

L20 S4-5

Answer 1

Extracellular:

• 4.2 +/- 0.3 mEq/L
• increases can lead to cardiac arrhythmia, fibrillation, or arrest
• kidneys precisely regulate extracellular potassium
• ~2%

Intracellular:

• 140 mEq/L
• ~98%

Question 2

Where in the nephron is potassium reabsorbed and secreted?

L20 S10

Answer 2

Reabsorbed:

• proximal tubule
• ascending limb of Henle

Secretion:

• late tubule
• collecting duct

Question 3

Describe the mechanism by which high potassium intake regulates potassium excretion.

L20 S14

Answer 3

• high potassium intake increases plasma potassium concentration
• high potassium concentration directly increases secretion of potassium into collecting tubules by increasing flow rate
• high potassium also increases the secretion of aldosterone which also increases secretion of potassium into collecting tubules
• these lead to increased potassium excretion

Question 4

What effect does an increased sodium intake have on potassium excretion.

L20 S18-20

Answer 4

• increased plasma sodium reduces aldosterone secretion while increasing GFR and proximal tubule sodium reabsorption
• both increased GFR and increased proximal tubular flow rate increase distal tubular flow rate
• decreased aldosterone and increase distal tubular flow rate effectively cancel each other out in regards to potassium secretion/excretion

Question 5

Describe the mechanism through which decreased extracellular calcium is corrected for

Answer 5

• decreased calcium concentration increased parathyroid hormone secretion
• increased parathyroid secretion increases renal calcium reasorption, calcium release from bone, and vitamin D3 activation
• vitamin D3 activation increases intestinal reabsorption
• all of these increase calcium concentration

Question 6

Describe the process of phosphate excretion.

L20 S27

Answer 6

• phosphate is reabsorbed at a max rate of .1mM/min

- PTH increases phosphate concentrations while decreasing reabsorption resulting in increased excretion

Question 7

How do principal cells effect potassium regulation?

L20 S33

Answer 7

Secretion:

• sodium-potassium-ATPase pump in basolateral domain
• passive diffusion through into lumen

Controls of secretion:

• activity of sodium-potassium-ATPase pump
• electrochemical gradients
• permeability of luminal membrane

Factors stimulating secretion:

• increased extracellular potassium (increases pump activity increases aldosterone levels)
• increased aldosterone level
• increased tubular flow rate