Gene models + nephron function (2)

Question 1

What is reabsorbed in the loop of Henle?

Answer 1

-sodium
-chloride
-water
-calcium
-magnesium

Question 2

How does fluid move through the loop of Henle?

Answer 2

-arrives from proximal tubule
-moves down thin descending limb
-then moves up thin ascending limb
-then up thick ascending limb

Question 3

What is the water permeability of the the thin descending limb and what is reabsorbed here?

Answer 3

-very water permeable
-water moves out
-nothing reabsorbed

Question 4

What is the water permeability of the the thin ascending limb and what is reabsorbed here?

Answer 4

-not very water permeable
-permeable to sodium + chloride
-they move out

Question 5

What is the water permeability of the the thick ascending limb and what is reabsorbed here?

Answer 5

-water impermeable
-permeable to sodium + chloride
-they move out

Question 6

What protein channels are on which membranes of the cells of the thick ascending limb (TAL)?

Answer 6

On apical membrane:
-NKCC2
-ROMK (Kir1.1)
On basolateral membrane:
-ATPase
-Kir1.1
-CLCK
-Barttin

Question 7

How does the protein NKCC2 work?

Answer 7

-1 Na+, 2 Cl-, 1 K+ bind to the protein
-causes conformational change
-ions released into intracellular fluid environment
-works due to Na+ grad. from ATPase

Question 8

How does the sodium that enters via NKCC2 leave?

Answer 8

-via ATPase
-net Na+ reabsorption

Question 9

How does the chloride that enters via NKCC2 leave?

Answer 9

-via CLCK on basolateral membrane
-net Cl- reabsorption

Question 10

What is Barttin?

Answer 10

-a beta subunit (accessory protein)
-regulated CLCK channel
-in absence of Barttin, CLCK doesn’t work

Question 11

How does the potassium that enters via NKCC2 leave?

Answer 11

By Kir1.1

Question 11

Why does NKCC2 not work if potassium isn’t recycled by Kir1.1?

Answer 11

-potassium isn’t recycled
-results in low K+ conc. on apical membrane side
-wouldn’t be able to reabsorb Na+ or K+

Question 12

How are calcium and magnesium reabsorbed?

Answer 12

Paracellular transport

Question 13

Is Bartter’s syndrome recessive or dominant?

Answer 13

Recessive

Question 14

What are the symptoms of Bartter’s syndrome?

Answer 14

-salt wasting (losing sodium + chlorine in urine)
-polyuria (excreting higher urine vol.)

Question 15

What do individuals with Bartter’s syndrome have?

Answer 15

-hypotension (due to excreting water that would remain in blood)
-hypokalaemia
-metabolic alkalosis
-hypercalciuria (high Ca2+)

Question 16

How many types of Bertter’s syndrome are there?

Answer 16

5 types

Question 17

What do loop diuretics do?

Answer 17

-increase water loss in urine
-treatment for high blood pressure

Question 18

What reabsorption occurs in the early distal tubule?

Answer 18

-sodium
-chloride
-magnesium

Question 19

How does reabsorption occur across early distal tubule cells?

Answer 19

-sodium potassium ATPase on basolateral membrane decreases intracellular sodium
-sodium + chloride move in using NCC proteins on apical membrane
-potassium recycled using protein on basolateral membrane
-Mg2+ + Ca2+ ion enter via proteins on apical membrane + lost via proteins on basolateral membrane

Question 20

How do thiazide diuretics work on the NCC protein?

Answer 20

-block sodium + chloride co-transporter, preventing their reabsorption
-reduces water reabsorption

Question 21

What are thiazide diuretics used to treat?

Answer 21

High blood pressure

Question 21

Is Gitelman’s syndrome dominant or recessive?

Answer 21

Recessive

Question 22

What are the symptoms of Gitelman’s syndrome?

Answer 22

-salt wasting + polyuria
-hypotension
-hypokalaemia
-metabolic alkalosis
-hypocalciuria