Renal Transport Mechanisms

Question 1

Apical vs basolateral

Answer 1

Apical - at the lumen

Basolateral - at the interstitium

Question 2

% absorbed at: PCT
Glc
AA
urea
Na
K
PO4
Ca
Mg
water

Answer 2

100
100
50
70
70
70
70
30
70

Question 3

% absorbed at: Proximal straight tubule

PO4

Answer 3

15

Question 4

% absorbed at: thick ascending limb
Na
K
Ca
Mg

Answer 4

25
20
25
60

Question 5

% absorbed at: DCT
Na
Ca
Mg
H2O
urea

Answer 5

5
8
5
var
var

Question 6

& absorbed at: Collecting duct
Na
H2O
urea

Answer 6

3
var
var

Question 7

The PCT functions by reabsorbing mainly which 2 substances?

Answer 7

Glc

AA

Question 8

PCT is how permeable to water?

Answer 8

Highly

Question 9

Transcellular vs paracellar

Answer 9

Through the cell

Between cells

Question 10

Symport vs antiport

Answer 10

Symport couples 2 solutes in the same direction.

Antiport has one go one way and another go the other.

Question 11

What side is the Na/K pump on?

Answer 11

Basolateral

Question 12

Na/K main 2 functions:

Answer 12

Increase extracellular Na and decrease IC Na. Create a partially negative charge inside cell.

Question 13

Almost always, Na is resorbed how?

Answer 13

Actively and via transcellular route.

Question 14

Na/H exchanger

Answer 14

On apical membrane of PCT

1:1 ratio

Question 15

Draw the Na/H exchanger mechanism

Answer 15

Draw

Question 16

Cl reabsorption

3

Answer 16

1. More water than Cl is absorbed in the PCT, causing its conc. to increase along the tubule.
2. Cl is filtered at the glomerulus almost freely, so its conc is the same at the glomerulus or in the first part of the PCT.
3. Intraluminal conc. of Cl drives a passive diffusion from high to low conc. via the paracellular pathway.

Question 17

Paracellular movement is determined by the presence of what?

Answer 17

Tight junctions, which retard water movement.

Question 18

AQP-1

Answer 18

Present in PCT and descending limb

Question 19

AQP-2

Answer 19

Present in the CD and are under control of ADH

Question 20

Net water movement in the tubule is determined by which 2 factors?

Answer 20

Presence or absence of tight junctions.

Presence of aquaporins.

Question 21

Presence of tight junctions in the PCT, descending limb and ascending limb

Answer 21

PCT has many tight junctions and aquaporins, making it permeable to water.
Descending limb has no tight junctions (has loose junctions instead) and AQP-1.
Ascending limb has many tight junctions and no aquaporins. Totally impermeable.

Question 22

Water absorption in the PCT, LoH, and DCT

Answer 22

PCT is 67
LoH is 15 (only descending thin limb)
DCT is 0

Question 23

What hormones regulate water permeability in the late distal tubules and collecting duct?

Answer 23

AVP, ANP, BNP

Question 24

Glc is “almost” entirely absorbed in the PCT by which 2 transporters?

Answer 24

SGLT1 (90%) which is high affinity

SGLT2 (10%) which is low affinity

Question 25

How do SGLTs work?

Answer 25

They link the movement of Na down its conc gradient with the uphill movement of Glc.

Question 26

What is trying to be inhibited in the treatment of DM?

Answer 26

SGLT2 | Inhibit reuptake of Glc.

Question 27

What happens when too much Glc exists in the plasma?

Answer 27

After reaching the threshold (375), it is excreted in the urine causing a "sweet pee".

Question 28

Descending LoH permeabilities

Answer 28

Impermeable to Na Permeable to water Water leaves, increasing the osmolarity in the tubule.

Question 29

Ascending LoH permeabilities

Answer 29

Impermeable to water, so NaCl s resabsorbed and the filtrate becomes less concentrated.

Question 30

Why is the thick ascending limb termed the "diluting segment"?

Answer 30

Because it reabsorbs a high degree of solutes, causing a high degree of dilution of the filtrate.

Question 31

How does the ascending limb accomplish particle reclamation?

Answer 31

It has a high degree of Na/K ATPase along the basolateral membrane.

Question 32

Furosemide

Answer 32

Inhibits NaCl reabsorption by competing for Cl- binding site

Question 33

Na-K-2Cl cotransporter

Answer 33

1 Na, 1 K and 2 Cl are reabsorbed on the apical side of the cell.

Question 34

What is the set up during the Na-K-2Cl contransporter

Answer 34

Slide 34

Question 35

Thiazide diuretics block what channel? Where?

Answer 35

The Na-Cl channel in the DCT. | Therefore, NaCl stays in the tubuler lumen and water follows.

Question 36

How are thiazides useful in treating kidney stones?

Answer 36

They enhance Ca reabsorption in the DCT

Question 37

CD reabsorption depends mainly on: | Which ones?

Answer 37

``` The body's needs via hormones. Aldosterone - Na ADH - water PTH - Ca Otherwise it is fairly impermeable to water. ```

Question 38

Goals of aldosterone (4)

Answer 38

1. Act on thick segment of nephron loop, DCT, and cortical portion of CD. 2. Cause the body to retain NaCl and water 3. Reduce urine vol 4. Increase levels of K in the urine