Cortex (300 mOsm)
Outer Medulla (600 mOsm)
Inner Medulla (1200 mOsm)
TUBULAR METRICS
Descending Osmolarity
300
Ascending Osmolarity
1200 → 100
Low Volume
Hyperosmotic (1200 mOsm)
Mechanisms:
■ Descending Limb: Permeable to H₂O, impermeable to salt. H₂O leaves via osmosis.
■ Ascending Limb: Permeable to salt (Active transport pumps), impermeable to H₂O. Creates the hypertonic medulla.
■ Collecting Duct (ADH): Opens Aquaporins. If ADH is high, H₂O leaves to match the 1200mOsm deep medulla.
■ Descending Limb: Permeable to H₂O, impermeable to salt. H₂O leaves via osmosis.
■ Ascending Limb: Permeable to salt (Active transport pumps), impermeable to H₂O. Creates the hypertonic medulla.
■ Collecting Duct (ADH): Opens Aquaporins. If ADH is high, H₂O leaves to match the 1200mOsm deep medulla.