Lecture 17 : Physiology of the Renal System III - Tubular Reabsorption

Question 1

Nephron Diagram

Answer 1

Question 2

Notes about proximal tubule

Answer 2

The first 60% of proximal tubule is called the proximal convoluted tubule, the 2nd 40% is the proximal straight tubule.

Present in renal cortex.

Uses movement of Na+ down electrochemical gradient into epithelial cells to drive movement of other substances (eg, glucose, amino acids)

Uses Na+ / K+ ATPase and other mechanisms to move Na+ out of cell on basolateral membrane

Question 3

How does water move in the proximal tubule?

Answer 3

Via paracellular route (net outward hydrostatic and osmotic forces) and transcellular route (involving aquaporins)

Question 4

Where do molecules go in the proximal tubule?

Answer 4

Question 5

What is the fate of glucose in the proximal tubule?

Answer 5

90% of glucose is transported by low affinity / high capacity sodium glucose cotransporter 2. Rest is carried by sodium glucose cotransporter 1 (high affinity, low capacity)

Basolateral transport is by glut2 or glut1

Tubular maximum transport load for glucose is about 380 mg.min-1; 2.1 mmol.min-1

Question 6

Quantifying glucose uptake and excretion

Answer 6

Question 7

How is SGLT2 inhibited and why

Answer 7

Treatment for diabetes. Canagliflozin, dapaglifozin.

Inhibiting transporters causes glucosuria and blood glucose drops

Question 8

Cl- movement in the proximal tubule

Answer 8

Active and Passive

Main active movement is through antiporter for other anions (HCO3- or HCOO-)

Given absorption of HCO3- with charge difference balanced by Na+ absorbance, less Cl- is moved than Na+ in early proximal tubule. Given water is reabsorbed with Na+ and HCO3-, Cl- concentration modestly increases along proximal tubule.

As Cl- concentration increases towards end of proximal tubule, it drives passive paracellular Cl- movement down concentration gradient

Question 9

Active Secretion in Proximal Tubule

Answer 9

Look at rest of lecture from slide 17