7. Renal Physiology 4 - Collins

• How are amino acids reabsorbed in the PCT?

  luminal Na coupled secondary active transporter

  • coupled by passive basolateral efflux
• In normal condition, all amino acids are reabsorbed by PCT
• In what part of the tubules are sodium, chloride and bicarbonate reabsorbed the most?

  PCT
• how is chloride in the renal tubules

  • leakiness of epithelium - paracellular ionic transport
  • Cl channels and coupled transporter - transcellular transport

  
• Water are reabsorbed in the PCT by

  • paracellular
  • aquaporin

  
• Potassium reabsorbed in the PCT by

  • solvent drag
  • channel
  • paracellular diffusion

  
• Ca2+ reabsorbed in the PCT by

  • paracellular (primarily) mediated by CLDN2
  • dependent on transcellular sodium reabsorption driven by NHE3 and Na/K ATPase
• reabsorption of Na+ generates osmotic gradient for water reabsorption which drags other solutes --> called solvent drag
• What is crucial for tubular reabsorption?

  Na/K pump and sodium reabsorption
• oligopeptides - reabsorbed after being

  • hydrolyzed to amino acid
  • special H+/Oligopeptide cotransporter
• Proteins are reabsorbed by receptor mediated endocytosis
• Peritubular capillary oncotic pressure depends on?

  filtration amount or fraction - increases with higher filtration
• starling forces determine

  • reabsorption into the blood
  • degree of back leak
• What can decrease peritubular capillary reabsorption?

  • increase peritubular capillary hydrostatic pressure
  • decrease peritubular capillary colloid osmotic pressure
• Reducing peritubular capillary reabsorption - can do what?

  • decrease net reabsorption of solutes and water by
  • increase amount of solutes and water that leak back into lumen through tight junction
• PCT transport is regulated to match GFR

  • but distal part of the nephron is regulated by homeostatic regulation
• Glomerulotubular balance

  • if GFR changes - PCT reabsorption remain constant at about 67%
• Increase GFR = reabsorption increases