Proximal Tubular Transport - Muster Flashcards Preview

CRRAB II Week 2 - WLB > Proximal Tubular Transport - Muster > Flashcards

Flashcards in Proximal Tubular Transport - Muster Deck (13):
1

What is the contribution of the proximal tubule to the overall reabsorption of the GFR?

  • 2/3 of all filtered solutes and water are reabsorbed in the proximal tubule
    • ~66% of Na+, Cl-, H2O
    • 100% of glucose
    • 80% HCO3

2

What forces are contributing to the reabsorptive nature of the peritubular capillaries compared to filtrative nature of glomeruli?

  • Starling forces:
    • increased oncotic pressure in capillary due to filtration of solute and water
    • decreased hydrostatic pressure in capillary due to resistance
    • Net Result = large force towards reabsorption

3

How is sodium reabsorbed?

  • Na+ pumped out of proximal tubule cells against electrochemical gradient via Na+/K+ ATPase
    • higher concentration outside of capillary due to this pump
    • Na+ diffuses down concentration gradient into fenestrated capillary
  • Some Natags along with Cl- during paracellular movement
  • Higher [Na+] outside of capillary also due to:
    • basolateral Na+/HCO3- symporter

4

How is Chloride reabsorbed?

  • Increased [Cl-] gradient in late sections of proximal tubule => favorable for transcellular movement
  • Luminal side:
    • Formate/Cl- antiporter 
  • Basolateral side:
    • K+/Cl- symporter
    • Cl- channel
  • Para-cellular movement through tight junctions
  • Diffuses down concentration gradient into fenestrated capillary

5

How is glucoses reabsorbed?

  • Na+-Glucose symporters AKA Sodium-Glucose Linked Transporters (SGLTs)
    • transport of glucose against gradient with help of Na+ going down its gradient
      • Secondary Active Transport
  • Glucose leaves proximal tubule cell via carrier-mediated transport to interstitium
  • Diffuses down concentration gradient into fenestrated capillary

6

How are amino acids reabsorbed?

  • Na+-AA symporters
    • transport of AA's against gradient with help of Na+ going down its gradient
      • Secondary Active Transport
  • AA's leave proximal tubule cell via carrier-mediated transport to interstitium
  • Diffuses down concentration gradient into fenestrated capillary

7

How is bicarbonate reabsorbed?

  • Bicarbonate is created and put back into the blood stream (reclaimed)
    • CO2 + H2O => H2CO3 => HCO3- + H+
      • rxn sped up by Carbonic anhydrase
      • H+ will leave via Na+/Hantiporter
    • HCO3- then leaves proximal tubular cell via Na+/HCO3- symporter
  • Diffuses down concentration gradient into fenestrated capillary

8

How are weak organic acids and bases reabsorbed?

  • Monocarboxylic acids are transported into the proximal tubular cell via MCA/Na+ symporter
    • MCA's are pumped against concentration using energy from Na+ going down concentration gradient
    • Pump is saturable
    • MCA's leaves proximal tubule cell via carrier-mediated transport to interstitium
    • Diffuses down concentration gradient into fenestrated capillary

9

What are the three ways water is reasbsorbed?

  1. Diffusion (minor amount)
  2. Aquaporin
  3. Paracellular transport

10

What is primary active transport?

  • moves solute against electrochemical gradient
    • requires ATP!
    • e.g. ATPases 

11

What is secondary active transport?

  • One solute moves down electrochemical gradient to drive another solute against it's gradient

12

What is facilitated transport?

  • Facilitated diffusion across lipid bi-layer
    • e.g. Channels, carrier-mediated

13

What is diffusion?

  • Movement of solute down a gradient
  • Primary method across peri-tubular capillary and paracellular movement
    • better for non-charged solutes