GLOSSARY

Reabsorption is the process by which water and useful substances are returned from tubular fluid to the blood. Of the roughly 180 litres of filtrate made each day, only about 1–2 litres are excreted as urine; more than 99 percent of the water is reabsorbed.

Routes of Reabsorption

• Transcellular route: substances pass through the tubular cell, across the apical and then the basolateral membrane.
• Paracellular route: passage through the junctions between cells; used by water and some ions such as calcium and magnesium.

Share of Sodium Reabsorption by Nephron Segment

• Proximal convoluted tubule: about 65 percent.
• Loop of Henle: about 25 percent.
• Distal convoluted tubule: about 5 percent.
• Collecting duct: about 2–5 percent (regulated by aldosterone).

Hormonal Control