A large amount of glomerular fluid is formed per day. Of this, about

A comparison of the volume of the filtrate formed per day (180 litres per day) with that of the urine released (1.5 litres), suggests that nearly 99 per cent of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption. The tubular epithelial cells in different segments of nephron perform this either by active or passive mechanisms. For example, substances like glucose, amino acids, Na⁺, etc., in the filtrate are reabsorbed actively whereas the nitrogenous wastes are absorbed by passive transport. Reabsorption of water also occurs passively in the initial segments of the nephron.