The descending loop of Henle traverses cortex/medulla. Its main function is to create a concentration gradient in the medulla.
- Isotonic filtrate (~300 mOsm/L)
- Great amount of H2O reabsorption.
- Also some reabsorption of urea, K+, Na+, Cl-, Glucose, amino acids, lactate, phosphate, HCO3-
- Water is much more permeable than ions in the descending limb. Because of this H20 rapidly perfuses out of the lumen and the filtrate becomes hypertonic.
- Max tonicity is achieved at the bottom of the loop (in the medulla of the kidney).
- Hypertonic filtrate (~1200 mOsm/L)