4 Renal Tubule Function 1

Question 1

How much of the proximal tubule is convoluted or straight?

Answer 1

60% convoluted

40% straight

Question 2

What enhances the surface area of the proximal tubules?

Answer 2

microvilli forming a brush border

Question 3

What facilitates secondary active transport?

Answer 3

ion channels
exchangers
cotransporters

Question 4

What facilitates primary active transport?

Answer 4

pumps

Question 5

What is largely responsible for the movement of water?

Answer 5

Na+ movement creating an osmotic gradient

Question 6

How much water is reabsorbed by the proximal tubule?

Answer 6

by the end of the tubule 70% is reabsorbed

Question 7

How does sodium move out of the filtrate?

Answer 7

Na+ / K+ ATPase on the basolateral membrane removes the sodium from within the cell, so more can come in out of the filtrate

Question 8

How does water leave the filtrate?

Answer 8

AQP1, through the paracellular route because of the net outward hydrostatic and osmotic forces

Question 9

Is insulin reabsorbed in the proximal tubule, and what is its’ concentration like at the end?

Answer 9

No, high

Question 10

Is Urea reabsorbed in the proximal tubule, and what is its’ concentration like at the end?

Answer 10

Weakly reabsorbed

but its’ concentration is still higher at the end because it is reabsorbed slower than the rate of water

Question 11

Is chloride reabsorbed in the proximal tubule, and what is its’ concentration like at the end?

Answer 11

Weakly reabsorbed, but its’ concentration is still higher at the end because it is reabsorbed slower than the rate of water

Question 12

Are Na+ and K+ reabsorbed in the proximal tubule, and what are their concentrations like at the end?

Answer 12

they are reabsorbed, but their concentrations are the same at the end

Question 13

are carbonate ions reabsorbed in the proximal tubule, and what is the carbonate concentration at the end?

Answer 13

Yes, reabsorbed

Question 14

Are amino acids and glucose reabsorbed in the proximal tubule, and what are their relative concentrations at the end?

Answer 14

strongly reabsorbed, therefore much lower concentrations

Question 15

How is glucose reabsorbed in the proximal tubule?

Answer 15

SGLT’s in the apical membrane

GLUT’s in the basolateral membrane

Question 16

What are the different SGLT’s?

Answer 16

SGLT 2 (low, affinity but high capacity, letting through 1 Na+ at a time but transporting 90% of the NA+)

SGLT 1 (high-affinity / low capacity, letting through 2 Na+ at a time but transporting only 10% of Na+)

Question 17

what is the distribution of SGLT’s and GLUT’s like?

Answer 17

SGLT 2 and GLUT 2 early tubule

SGLT 1 and GLUT 1 late tubule

Question 18

what is the significance of tubular maximum transport?

Answer 18

for substances like glucose, which can be filtered out of the blood indefinitely depending on its’ concentration and GFR, if too much is in the blood then it will stay in the filtrate, as only so much can be reabsorbed

Question 19

Name 2 SGLT2 inhibitors

Answer 19

canaglifozin

dapaglifozin

Question 20

What are SGLT2 inhibitors used for?

Answer 20

to treat diabetics

Question 21

What is plasma amino acid concentration?

Answer 21

2.5 - 3.5 mM

Question 22

What are most amino acid transporters like?

Answer 22

cotransporters of Na+

use the sodium gradient to pull amino acids out of the filtrate

Question 23

How does HCO3- leave the filtrate?

Answer 23

equilibrium in filtrate to form H2O and CO2, pass over membrane, equilibrates to re-form H+ and HCO3-, HCO3- then leaves the cell

Question 24

How does HCO3- leave the basolateral membrane of the proximal tubule?

Answer 24

3 HCO3- / Na+ symporter

Question 25

What facilitates the equilibration of HCO3-?

Answer 25

carbonic anhydrase

Question 26

What does acetazolamide do?

Answer 26

blocks carbonic anhydrase, acting as a weak diuretic, although it is not used anymore

Question 27

What would acetazolamide be used for?

Answer 27

glaucoma

mountain sickness prophylaxis

Question 28

What is one effect of acetazolamide on urine?

Answer 28

makes it more alkaline, leading to metabolic acidosis

Question 29

How does caffeine lead to diuresis?

Answer 29

antagonist to adenosine (A1) receptor
increases glomerular filtration rate by opposing the vasoconstriction of renal afferent arteriole
inhibits Na+ reabsorption at proximal tubules
water reabsorption is hence inhibited

Question 30

How does Cl- get absorbed by proximal tubule endothelium from the filtrate?

Answer 30

uses an antiporter for other ions like HCO3- or HCOO-

Question 31

Why is less Cl- moved than Na+ in the early proximal tubule?

Answer 31

reabsorption of HCO3-

charge difference balanced by Na+ absorption

Question 32

What happens to Cl- concentration over the proximal tubule and what is the effect of this?

Answer 32

it increases as sodium pulls out water

this drives passive paracellular Cl- movement

Question 33

How does the proximal tubule reabsorb albumin?

Answer 33

endocytosed by filtrate plasma membrane

catabolised into its amino acids for recycling

Question 34

Name 3 organic anions actively secreted in the proximal tubule into the filtrate from the blood

Answer 34

penicillin
P-aminohippuric acid
Furosemide

Question 35

How are organic anions secreted?

Answer 35

basolateral membrane - organic anion transporters (OAT)

luminal membrane - multidrug resistance associated protein (MRP)