Question

The movement of substances from the filtrate back into the blood is called .

• A. tubular secretion
• B. tubular reabsorption
• C. back flow
• D. filtration

Answer 1

The correct option is B tubular reabsorption

Tubular reabsorption is the movement of substances into the blood from the filtrate. 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. The tubular epithelial cells in different segments of nephron perform this either by active or passive mechanisms. For example, substances like glucose, amino acids, ${\mathrm{Na}}^{+}$, 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