Reabsorption
In renal physiology, reabsorption, more specifically tubular reabsorption, is the process by which the nephron recovers water and solutes from the tubular fluid (pre-urine) and returns them to the circulating blood. It is called reabsorption (and not absorption) because these substances have already been absorbed once from ingested food and water (particularly in the intestines) and the body is reclaiming them from a fluid stream filtered out of blood in the glomeruli that is on its way to becoming urine.
Each day, the kidneys filter about 150 liters of blood, while only about 1.5 liters of urine is actually expelled from the body. Reabsorption thus recovers a large proportion of the water filtered by the kidneys and plays a critical role in maintaining the water balance of the body.