Renal Physiology 6 - Checked and Complete

Question 1

What is a typical range for serum potassium?

Answer 1

~3.6 - 5.2 mEq/L

Question 2

How can muscles regulate serum potassium?

Answer 2

They can uptake potassium if the concentration becomes to high

Question 3

What hormones help sweep up serum potassium into muscle?

Answer 3

Epinephrine and Insulin

Question 4

How does insulin/epinephrine work molecularly in regard to potassium?

Answer 4

Stimulate Na/K ATP pump activity

Question 5

How does acidity/alkalinity affect serum potassium?

Answer 5

Acidosis (i.e. high plasma H+ concentration) promotes net K+ movement out of cells.

**Alkalosis does the opposite - potassium into cells. **

Question 6

Where is the majority of potassium reabsorbed in the nephron?

Answer 6

80% in the PCT

Question 7

List percentages of Potassium absorbed in the Nephron and where

Answer 7

80% PCT
10% Thick ascending limb

6-20% Collecting Duct

Question 8

How is K+ reabsorbed in the PCT?

Answer 8

Passive paracellular diffusion through tight junctions

Question 9

How is K+ reabsorbed in the thick ascending loop of Henle?

Answer 9

via the Na-K-2Cl symporter in apical membrane

Question 10

How do the DCT and collecting duct contribute to K+ reabsorption during periods of low dietary K+?

Answer 10

They do very little (can remain inert and by so doing potassium is reabsorbed very well)

2% reabsorbed at DCT

6% reabsorbed at collecting duct

Question 11

How does the DCT and collecting duct contribute to potassium control when potassium is normal/high in the diet?

Answer 11

**The DCT can secrete up to 150% of filtered potassium load. **

The collecting duct always absorbs, but cannot capture that much potassium

Question 12

Which area of the nephron is MOST responsible for K+ secretion?

Answer 12

Cortical collecting duct

This is more than DCT

Medullary collecting duct only absorbs

Question 13

Which cells mediate secretion of potassium? Which regulate secretion?

Answer 13

The principle cells mediate K+ secretion.

The intercalated cells mediate K+ reabsorption.

Question 14

Describe K+ secretion mechanism in principle cell

Answer 14

Sodium/Potassium pump actively brings potassium into the cell

Potassium accrues inside cell, leaves out of apical membrane via potassium channel

Question 15

How can Potassium secretion be regulated?

Answer 15

Apical potassium channels can be open or closed via aldosterone

Opening or closing apical sodium channels such that sodium cannot find its way inside the cell to be used by the sodium/potassium pump

Low or high plasma levels of potassium to be placed into the interstitium and build a gradient to be transported

Tubular potassium levels and flow rates - Low flow rate = potassium accumulates more than usual in nephron = less is secreted and usual amount absorbed

Question 16

Describe how Potassium and Aldosterone regulate each other

Answer 16

Rise in serum potassium changes the surface membrane potential of adrenal cells to modulate aldosterone release

Aldosterone opens apical potassium channels and stimulates the basolateral sodium/potassium pump so more potassium is secreted

Question 17

How does increased serum potassium increase potassium secretion independent of aldosterone?

Answer 17

Potassium builds up in serum = builds up in interstitium = more substrate for sodium/potassium pump and stronger gradient = more secreted

Question 18

How does tubular flow affect potassium secretion?

Answer 18

Increased tubular flow = more potassium secretion

Question 19

What is an unwanted side effect of a diuretic?

Answer 19

Increases Potassium secretion into urine

Question 20

What is a ‘potassium-sparing’ diuretic?

Answer 20

A diuretic that acts on the collecting duct principle cells so tubular flow is not super fast before that, leading to excess potassium secretion

Question 21

Why would a potassium-sparing diuretic not be chosen?

Answer 21

Not as effective as other kinds of diuretics

Question 22

Describe hyper and hypo calcemia

Answer 22

Hypocalcemia = increased excitability of nerves and muscles which may lead to muscle spasms and/or hypocalcemic tetany

Hypercalcemia = reduced excitability leading to lethargy and even cardiac arrhythmias

Question 23

What are the effects of PTH?

Answer 23

1) promoting active vitamin D formation

2) moving Ca2+ from bone to blood

**3) promoting renal Ca2+ reabsorption **

Question 24

What is the body’s store for calcium? What is the body’s store for potassium?

Answer 24

Bone

Muscle

Question 25

Describe calcium handling in the nephron

Answer 25

PCT absorbs ~60% (passive paracellularly)

DCT uses Ca²⁺/ATP pumps or Ca²⁺/Na⁺antiporter in basolateral membrane; channel in apical membrane

Question 26

Describe phosphate handling in the nephron

Answer 26

~75% reabsorbed in PCT transcellularly via Sodium/Phosphate symporter in apical membrane

Question 27

What is the result of PTH on phosphate?

Answer 27

PTH acts to inhibit proximal phosphate reabsorption

Greater excretion of phosphate via urine

Triggered by high phosphate serum levels

Question 28

How much of the calcium in plasma is free/bound ALSO filtered/unfiltered?

Answer 28

50/50

Question 29

Describe the T_M of phosphate reabsorption.

Answer 29

The Tm is very close to the filtered phosphate load.

MEANING, even a small increase in filtered phosphate results in more phosphate being excreted