What is the process by which the tubular cells secrete substances into the filtrate?

Step-by-step solution

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. 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 pa