Loop of Henle

• Loop of Henle

  • 1 cell thick wall
  • Thinner + thicker regions of loop
  • Reflect lumen diameter differences
  • Different regions have different permeabilities to water, sodium and chloride ions
  • Medulla region
  • Close to collecting ducts
  • Vasa recta (capillary network) lie adjacent
  • Increased salt concentration lowers medulla WP
  • More water reabsorbed from filtrate
  • Enters vasa recta blood capillaries
  • Hypertonic urine
  • Countercurrent multiplier system:
  • Hairpin arrangement (2 limbs close)
  • Fluid flows opposite directions
  • Longer loop greater countercurrent multiplier effect
• Mammal adaptations for dry habitats

  • Longer loops of henle in deeper medulla tissue
  • Create higher salt concentration so more water re-absorbed
  • More permeable collecting ducts (ADH sensitive + more aquaporins in luminal membranes)
  • Metabolic water
  • Eat seeds with storage molecules like lipid
  • When aerobically respired, produces water
  • 1 lipid gram produces 2x more metabolic water than 1 carbohydrate gram
• Limbs

  Ascending

  • Ion permeable but water impermeable
  • Na+ + Cl- ions diffuse out to medulla in lower + thinner regions
  • Upper, thicker regions they’re actively pumped out
  • Net effect:
  • Top, filtrate hypertonic to blood (lower solute concentration)
  • Salty medulla tissue (Na^+ + Cl- ions); tissue fluid low WP

  Descending

  • Filtrate enter PCT isotonic to blood plasma
  • Give filtrate high solute concentrate, hypertonic
  • Has aquaporins
  • High water permeable
  • Diffuses filtrate to medulla
  • Slight permeable to Na+ + Cl- ions
  • Slowly diffuse medulla to filtrate
  • Facilitated diffusion