Ascending limb

Descending limb

Thick

Nephric filtrate becomes hypotonic.

Impermeable to water.

Active reabsorption of 25% K⁺ and small amount of CI^–

Thin

Nephric fitrate becomes hypertonic.

Permeable to water.

No active reabsorption of Na⁺ ion. It receives Na⁺ by diffusion.