Tubular Transport

Question 1

What is the movement of solutes across the renal tubular epithelium between cells called?

Answer 1

Paracellular movement

Question 2

What is the movement of solutes through the cells called?

Answer 2

Transcellular movement

Question 3

What is involved in ‘active transport’?

Answer 3

Direct coupling of ATP hydrolysis to a transport process in the cell membrane - primary active transport

Question 4

What is the most important primary active process in the nephron?

Answer 4

Na+/K+ ATPase

Question 5

Where is the Na+/K+ ATPase located?

Answer 5

On the basal (and basolateral) side of the cells lining the nephron

Question 6

What transporter accounts for much of the oxygen consumption of the kidney?

Answer 6

Na+/K+ ATPase

Question 7

What are the other primary active transport mechanisms in the nephrons?

Answer 7

Ca2+ ATPase, H+ K+ ATPase

Question 8

What is involved in ‘secondary active transport’?

Answer 8

Ionic gradients across the nephron cell membranes acting as driving forces for the reabsorption or secretion of many other solutes

Question 9

What is the most important driving force for secondary active transport?

Answer 9

Sodium gradient

Question 10

What are ENaC? Where are they located?

Answer 10

Epithelial Na Channel - located through out the nephron on the apical membrane of the cells

Question 11

What drug closes the ENaC?

Answer 11

Amiloride

Question 12

What proteins are tight junctions constructed of?

Answer 12

Occludin, claudins, junctional adhesion molecules

Question 13

Is water reabsorption active or passive?

Answer 13

Passive

Question 14

How does water movement occur in the nephron?

Answer 14

Water osmotically follows solute absorption

Question 15

What channel allows reabsorption of water?

Answer 15

Aquaporins

Question 16

Where are AQP-1 channels located?

Answer 16

Widely distributed in the body e.g. in lung and brain cells, and kidneys

Question 17

Where are AQP-2 channels located?

Answer 17

In the collecting tubules

Question 18

What is the incorporation of AQP-2 into the collecting tubule cell apical membranes controlled by?

Answer 18

ADH

Question 19

Where are AQP-3 channels located?

Answer 19

In the basolateral membranes of the collecting tubule cells

Question 20

What is the function of AQP-3?

Answer 20

Allows the cells to maintain homeostasis even when there is no AQP-2 incorporated in the apical membranes
When AQP-2 is installed in the apical membranes, AQP-3 allows water reabsorbed across the apical membrane via AQP-2 to leave the cells across the basal membrane and enter the interstitium

Question 21

What is the process of water moving paracellularly, carrying some solutes with it?

Answer 21

Solvent drag