Medicine & USMLE

Proximal Tubule

  1. Renin
  2. Angiotensin II
  3. Aldosterone
  4. ADH
  5. RAAS System
  6. Kidney Overview
  7. Nephron Structure
  8. Glomerulus
  9. Proximal Tubule
  10. Loop of Henle
  11. Distal Tubule
  12. Collecting Duct
  • Proximal (Convoluted) Tubule 
    • First segment the filtrate traverses after glomerular filtration 
    • Two major roles
      • Reabsorption of solutes
        • Majority of solute reabsorption occurs in early proximal tubule
        • Na+
          • Major ion undergoing reabsorption by Na+/K+ ATPase and Na/H antiporters
          • Always coupled to chloride and water reabsorption 
        • Water
          • Water is reabsorbed paracellularly by passive diffusion through tight junctions or by facilitated diffusion via aquaporins 
        • Important nutrients
          • Includes amino acids, vitamins, salts, glucose, bicarbonate, water
      • Secretion of waste
        • Commonly secreted solutes include H+, urea, ammonia, K+ 
    • Overall effect:
      • Amount of filtrate in nephron is reduced 
      • Solute composition in nephron is altered
      • But overall concentration of solutes does not change