. Thin and thick limbs of Henle: Extends into the kidney medulla and returns as the thick limb to the cortex. The content of the descending thin limb becomes increasingly hypertonic as salt (active chloride pump) is actively transported from the ascending limb into the interstitial space surrounding the descending thin limb. Chloride, together with sodium ions, passively enters the descending limbs, as water is drawn to the interstitium. Unlike the descending limb, the ascending limb of the loop of Henle is impermeable to water, and the content of the ascending limb of the tubule becomes increasingly hypotonic as salt is actively transported from it. Sodium ions are actively reabsorbed, and water is passively reabsorbed in the distal tubule.