Formation of Dilute Urine

Tubule Osmolarity

↑ in descending limb
↓ in ascending limb
↓ in collecting duct

Urine Production

Fluid intake is highly variable.
Homeostasis requires maintenance of fluid volumes within specific limits.
Urine concentration varies with ADH.

High intake – Dilute urine of high volume
Low intake – Concentrated urine of low volume

Glomerular filtrate and blood have the same osmolarity – 300mOsm/Liter
Tubular osmolarity changes due to a concentration gradient in the medulla

When dilute urine is formed, osmolarity in the tubule
Increases in the descending limb
Decreases in the ascending limb
Decreases more in the collecting duct