10. Transport of amino acids, glucose, urea and suplphate

Question 1

Where is glucose reabsorbed?

Answer 1

Virtually all filtered glucose is reabsorbed in the proximal convoluted tubule

Question 2

How is glucose reabsorbed?

Answer 2

• Na+K+ ATPase pump on apical surface pumpm Na out and K+ in
• creates conc gradient for Na+
• Na+ moves unti cell from tubule via SGLT1/2 with glucose
• glucose moves into blood through GLUT on apical surface

Question 3

What is Tm?

Answer 3

Tm is the maximum tubular resorptive capacity for a solute

Question 4

When does glycosuria develop?

Answer 4

• There is a limited number of Na+/glucose carriers, so glucose reabsorption is Tm limited.
• If plasma glucose rises above 10mmol/L (as in diabetes) glycosuria will develop.

Question 5

Why is glycosuria normal in pregnancy?

Answer 5

Tm for glucose falls, and glucose is excreted in the urine

Question 6

Where and how are amino acids reabsorbed?

Answer 6

• Reabsorbed in the proximal convoluted tubule by secondary active transport
• Symport with Na+, driven by Na+/K+ ATPsae as with glucose

Question 7

how is urea reabosrbed?

Answer 7

• Urea concentration increases in the filtrate as a result of Na+, Cland water reabsorption
• Allows passive reabsorption 40- 50% of urea down concentration gradient
• Distal tubule and outer medulla ducts are impermeable to urea