Tubular Function:  Chapter 17

Reabsorption in PCT: Fig 17.13 &  Fig 17.14
Secretion / Reabsorption: Fig 17.19

Reabsorption in the PCT :  Fig 17.15
Active transport of Na+, glucose, amino acids, and phosphate (HPO₄^-2 & H₂PO₄^-)
Water and Cl- usually follow the charge and osmotic gradients

 

Reabsorption:
Active, therefore specificity and saturation
Amino acids --> neutral, acidic, and basic sites

Tmax (tubular maximum)
Energy from ion gradients (co-transport or symport) or ATP

Reabsorption in PCT:

As with any transport system, saturation occurs at high [plasma]_solute , giving a maximum rate of reabsorption or a T_max for each reabsorbed solute.
T_max depends upon # of transport sites
 
 
 

Reabsorption in PCT: Fig 17.16
Na⁺ Reabsorption in PCT: Fig 17.17
Na⁺ Reabsorption in DCT: Fig 17.17
Cell-Cell Junctions in CTs: Fig 17.18
 
 

PCT & DCT Secretion
• Organic Anions
• Phenol Red
• PAH
• Creatinine
• Penicillin
• Acetazolamide
• Furosemide
• PCT & DCT Secretion
• Organic Cations
• Histamine
• Norepinephrine
• Quinine
• Creatinine

QUESTION:
If secretion is a carrier mediated process, how does one explain the presence of transport sites for solutes not found in nature?

[Solute]_nephron
Blood = 300 mOsm
Bowman’s Capsule = 285 mOsm
PCT = 285 mOsm
Loop of Henle = 285 ---> 1,200 ---> 200 mOsm
DCT = 200 ---> 100 ---> 200 mOsm
CD = 200 ---> 285 ---> variable to 1,200 mOsm  - [ADH] dependent