L05: Renal Tubular Function

Question 1

Which structure of the nephron comes after the bowmans space

Answer 1

Proximal tubule

Question 2

What are the 2 parts of the proximal tubule

Answer 2

Proximal convoluted tubule

Proximal straight tubule

Question 3

Where is the proximal tubule found in relation to the kidney Cortex to medulla

Answer 3

Cortex

Question 4

What are the 2 membranes of the proximal tubule

Answer 4

Apical membrane

Basolateral membrane

Question 5

Which substances are absorbed in the proximal tubule

Answer 5

Sodium 
Potassium 
Bicarbonate 
Chloride 
Urea 
Glucose
Amino acids 
Water

Question 6

How is water reabsorbed in the proximal tubule

Answer 6

By aquoporin 1 channels present on the apical and basolateral membrane
And/or
Between cells

Question 7

How is glucose reabsorbed in the proximal tubule ? Describe the channels involved.

Answer 7

At apical membrane:
1) SGLT2 brings in 1 sodium and 1 glucose molecule on the apical membrane
2) SGLT1 brings in 2 sodium and 1 glucose molecule
Reminder: SGLT1&2 use the electrochemical gradient of sodium to bring in glucose.

At basolateral membrane:

3) glucose from SGLT2 leaves through the basolateral membrane by GLUT2
4) glucose from SGLT1 leaves through the basolateral membrane by GLUT1

Question 8

To treat diabetes by lowering glucose levels what can we do to the SGLT2 channel

Answer 8

Inihbit it

So more glucose is lost in the urine

Question 9

How is bicarbonate ions reabsorbed

Answer 9

1) water and carbon dioxide join inside the cell with carbonic anhydrase enzyme to form H2C03 which dissociates into hydorgen and bicarbonate ions
2) on the basolateral membrane bicarbonate is taken by 3hc03-/na+ cotransporter
3) hydrogen ions leave through the apical membrane from inside the cell by a na+/h+ exchanger
4) sodium that is brought into the cell becomes reabsorbed through the basolateral membrane by 3na+/2k+ pump.

Question 10

How can be inhibit carbonic anhydrase in order to make the urine more alkaline

Answer 10

Aceta zolamide

Question 11

How is chloride ions reabsorbed in the proximal tubule?

Answer 11

1) methonate acid enter the cell to form methonate ion and hydrogen ion ions
2) methonate leaves the cell and enters back to the filtrate by a chloride exchanger which brings in chloride in return at the apical membrane
3) chloride leaves through the basolateral membrane via chloride channels.

And/or

Chloride moves between cells

Question 12

How are amino acids in the proximal tubule reabsorbed

Answer 12

amino acids are reabsorbed through the apical membrane and leave the basolateral membrane by amino acid transporters .

Question 13

What effect does caffeine have on reabsorption in the proximal tubule

Answer 13

Inhibits sodium reabsorption

Question 14

If albumin enters the filtrate how is it reabsorbed in the proximal tubule

Answer 14

Albumin is endocytosed

Catabolised into amino acids and reabsorbed

Question 15

Apart from reabsorption of substances in the proximal tubule what other role does the proximal tubule have

Answer 15

Secret organic anions that are not wanted in the body

Question 16

How does the proximal tubule actively secrete organic anions into the filtrate so it becomes removed with the urine?

Answer 16

On basolateral membrane:
Organic anion transporters bring in the anion into the cell

On the apical membrane
Organic anion leaves by multi drug resistance associated proteins (MRP)