Loop of Henle

Concentrates urine
Three segments:

  1. thin descending
  2. thin ascending
  3. thick ascending

loop of henle schematic.png

Segment Permeability to water What happens here?
Thin descending +++ 20% water reabsorbed here
Thin ascending - active reabsorption of sodium, chloride, and potassium
ENAC
Thick ascending - ROMK channels

countercurrent exchange in the vasa recta preserves ↑ osmolarity in renal medulla

copied shamelessly from Guyton:

Mechanism by which the medullary interstitium becomes hyperosmotic = countercurrent multiplier

  • absorption of NaCl by thick ascending limb + continuous inflow of NaCl from proximal tubule

Special characteristics that make this possible:

  1. low medullary blood flow = minimize solute loss from the medullary interstitium.
  2. The vasa recta serve as countercurrent exchangers, minimizing washout of solutes from the medullary interstitium.

#renal