USMLE

Loop of Henle

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Renal
  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
  • Loop of Henle
    • Two-limbed (U-shaped) structure that extends into medulla
      • Different parts of the loop have different permeabilities. 
      • Descending Limb
        • Extends from cortex down into the relatively salty medulla 
        • Highly permeable to water but impermeable to NaCl
          • Reabsorption of water only by facilitated diffusion
      • Ascending Limb
        • Ascends from medulla back to the cortex
        • Permeable to NaCl (salt) but impermeable to water
          • Reabsorption of ions only by passive + active transport
      • Vasa recta is a capillary system running parallel to loop that returns water and solutes to the bloodstream
    • Opposite flows (countercurrents) interact to increase (multiply) interstitial concentration gradient, known as countercurrent multiplication
      • Active reabsorption of NaCl in ascending limb increases passive water reabsorption in descending limb 
      • Structure causes gradient where solute is most concentrated at the bottom of the loop
      • The longer the loop, the more the gradient “multiplies”, causing more water to be reabsorbed by the body.