Unit 2, L15 Tubular Functions along the Nephron

Question 1

Euvolemia is achieved when

Answer 1

Whenever Na excretion matches Na intake, meaning Na balance leads to steady state ECV

Question 2

What percentage of Na is reabsorbed in the proximal convoluted tubule

Answer 2

67%

Question 3

What percentage of Na is reabsorbed in the thin descending limb

Answer 3

0%

Question 4

What percentage of Na is reabsorbed in the thin ascending limb

Answer 4

0%

Question 5

What percentage of Na is reabsorbed in the thick ascending limb

Answer 5

25%

Question 6

What percentage of Na is reabsorbed in the distal convoluted tubule

Answer 6

5%

Question 7

What percentage of Na is reabsorbed in the collecting duct

Answer 7

3%

Question 8

Isosmotic reabsorption of Na only happens where

Answer 8

In the proximal tubule

Question 9

In the early proximal tubule, Na+ is reabsorbed primarily with ___________

Answer 9

HCO3- and organic solutes such as glucose and amino acids

Question 10

In the late proximal tubule, Na+ is reabsorbed primarily with ________

Answer 10

Cl-

Question 11

By the time the glomerular filtrate reaches the midpoint of the proximal tubule, what following modifications have been made because of the secondary active transport processes?

Answer 11

100% of the freely filtered glucose and amino acids have been reabsorbed
85% of the filtered HCO3- have been reabsorbed
Most of the filtered phosphate, lactate, and citrate have been reabsorbed
Na+ reabsorption is coupled to each ofhtese transport processes, so its been extensively reabsorbed

Question 12

In the early proximal convoluted tubule, reabsorption of Na is coupled with HCO3-, what does this do for reabsorption of Cl-

Answer 12

There is a negative transepithelial voltage that provides the driving force for paracellular reabsorption of Cl0

Question 13

In the late proximal convoluted tubule, Na+ transport is largely accompanied by _____

Answer 13

Cl- reabsorption by both transcellular and paracellular pathways

Question 14

Concentration of glucose along the PCT

Answer 14

The overall concentration should be the same in Bowman’s space as in the plasma
As it goes through the proximal tubule, it is being reabsorbed

Question 15

Concentration of Na along the PCT

Answer 15

Concentration is high and its being moved along with water all the way along, so its movement, in terms of concentration, is going to be the same all the way along the proximal tubule. It is isosmotic

Question 16

Three segments of the loop of Henle

Answer 16

Thin descending limb, thin ascending limb, and thick ascending limb

Question 17

Thin descending limb permeabilities

Answer 17

Thin descending limb is IMPERMEABLE to Na and Cl, but PERMEABLE to H2O

Question 18

Thin ascending limb permeabilities

Answer 18

Thin ascending limb is PERMEABLE to Na and Cl but IMPERMEABLE to H2O

Question 19

Thick ascending limb permeabilities

Answer 19

IMPERMEABLE to water, so Na is being reabsorbed but H2O is not following, so urine is getting more and more diluted (as water is getting left behidn)

Question 20

In the thick ascending limb, what is the movement and gradients

Answer 20

1) Active pumping by Na/K/ATPase in the basalateral membrane, sends Na out and K in
2) This causes low Na concentration inside the cell
3) This produces a chemical gradient for Na to move from the tubular fluid and into the cell

Question 21

What part of the nephron is the site of action for diuretics?

Answer 21

Thick ascending limb

Question 22

At max doses, loop diuretics will inhibit what

Answer 22

Completely inhibit NaCl reabsorption in the TAL and result in excretion of 25% of filtered Na

Question 23

The early distal tubule reabsorbs what percentage of filtered Na

Answer 23

5%

Question 24

Permeabilities of the early distal tubule

Answer 24

IMPERMEABLE to water

Question 25

Transporters and movements in the early distal tubule

Answer 25

Na and Cl enter the cell through the Na-Cl cotransporter
Na is extruded from the cell into the blood by the Na/K/ATPase
Cl diffuses out of the cell through Cl channels in the basolateral membraned

Question 26

Late distal tubule and collecting duct will reabsorb what percentage of filtered Na

Answer 26

3%

Question 27

Two major cell types along the late distal tubule and collecting duct

Answer 27

Principal cells and alpha and beta intercalated cells

Question 28

Principal cells are involved in

Answer 28

Na reabsorption, K secretion, and water reabsorption

Question 29

Late distal tubule and collecting duct movement and transporters

Answer 29

Luminal membrane of the principal cells contain epithelial Na channels (ENaC)
High negative potential on luminal side caused by reabsorption of Na
Driving force for paracellular reabsorption of Cl-
Site of K secretion

Question 30

Alpha intercalated cells are involved in

Answer 30

K reabsorption and H secretion

Question 31

Beta intercalated cells are involved in

Answer 31

HCO3- secretion and reabsorption of H and Cl

Question 32

Major functions, cellular mechanisms, and diuretics:

Early PT

Answer 32

Isosmotic reabsorption of solute and water
Mechanism: Na+-glucose, Na+-amino acid, Na+-phosphate cotransport
Osmotic diuretics

Additionally,
Mechanism: Na+-H+ exchange
Carbonic anhydrase inhibitos

Question 33

Major functions, cellular mechanisms, and diuretics:

Late PT

Answer 33

Isomotic reabsorption of solute and water
Mechanisms: NaCl reabsorption driven by Cl- gradient
Osmotic diuretics

Question 34

Major functions, cellular mechanisms, and diuretics:

TAL

Answer 34

Isosmotic reabsorption of NaCl without water, dilution of tubular fluid, and reabsorption of Ca2+ and Mg2+
Mechanism: Na-K-2Cl- cotransport
Loo diuretics

Question 35

Major functions, cellular mechanisms, and diuretics:

Early DT

Answer 35

Reabsorption of NaCl without water, dilution of tubular fluid
Mechanism: Na-Cl cotransport
Thiazide diuretics

Question 36

Major functions, cellular mechanisms, and diuretics:

Late DT and CD (principal cells)

Answer 36

Reabsorption of NaCl, K+ Secretion, and Variable water reabsorption
Mechanism: Na channels (ENaC), K channels, and AQP2 channels
K+ sparing diuretics

Question 37

Major functions, cellular mechanisms, and diuretics:

Late DT and CD (alpha intercalated cells)

Answer 37

Reabsorption of K and secretion of H
Mechanism: H+/K+/ATPase, and H+/ATPase
K+ sparing dirretics