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Flashcards in Lust 1 & 2 Deck (6)
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1

Proximal Tubule

  • Primary Recovery Segment
  • Bulk Recovery: Selective Reabsorption=iso-osmotic
    • H2O
    • Electrolytes
    • Glucose 
    • Amino Acids
  • Transporter: Crosses transepithelial
    • Na 
    • HCO3  (85% reabsorbed)
    • Glucose
    • Amino Acids
    •  Ca2+ (not PTH dependent)
  • Diffusion=paracellular-follow osmotic gradient
    • water 
    • urea
    • Cl 
    • K

2

Proximal Tubule: Mechanism

  • Na+/K+-ATPase drives rxn
    • Basolateral side=Interstitial
    • Set up a gradient for:
      • K+ (w/water) to move in paracellularly
      • Na+ to move passively through passive channel
        • Na+ channel on apical side
  • CO2 diffuses readily through cell membrane 
  • Particles make Interstitial fluid Transiently Hypertonic
    • taken up into peritubular capillaries

3

Proximal Tubule: Na+ is coupled to

  • All on apical side (lumen)
    • Na/glucose transporter
    • Na/amino acid transporter
    • Na/H transporter

4

Proximal Tubule: Bicarbonate Shuttle

  • 85% Reabsorbed
  • Carbnonic Anhydrase
    • critical for shuttle 
    • lumen and epithelial cell
  • H+ fuels Na/H exchanger on apical side
  • Na/H exchanger (apical membrane)
    • H+ enters lumen and combines with HCO3- to form H2CO3
    • H2CO3--> CO2+ H2O 
      • via Carbonic Anhydrase
    • H2O moves paracellularly to Interstitium
    • CO2 diffuses into epithelial cell and forms H2CO3
    • H2CO3--> HCO3- + H+ 
      • via CA
    • HCO3- to IF via:
      • Na/HCO3- Cotransport 
      • Cl-/HCO3 exchange
    • H+ repeats cycle to Na/H exchanger

5

Proximal Tubule: What happens if CA is removed from epithelial cells

  • Decreases Na+ transport
  • Decreases H2O movement (follows Na+)

6

Glucose

  • Glucose Transporters
    • Transporter Max >280