A large quantity of fluid is filtered everyday by the nephrons in the kidneys. Only about 1% is excreted as urine. The remaining 99% of the filtrate
Only part of the fluid is excreted along with the waste material because 99% of the filtrate is reabsorbed into the blood. Urine consists of water alone 95% and inorganic and organic matter 5%. A comparison of the volume of the filtrate formed per day (180 litres per day) with that of the urine released (1.5 litres), suggest that nearly 99
per cent of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption.