Lust 1 & 2

Question 1

Proximal Tubule

Answer 1

• 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

Question 2

Proximal Tubule: Mechanism

Answer 2

• 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

Question 3

Proximal Tubule: Na+ is coupled to

Answer 3

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

Question 4

Proximal Tubule: Bicarbonate Shuttle

Answer 4

• 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

Question 5

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

Answer 5

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

Question 6

Glucose

Answer 6

• Glucose Transporters
  
  • Transporter Max >280