Function of the nephron and the formation of urine

Every day, about 160–180 litres of plasma are filtered (assuming glomerular filtration rate (GFR) is 120–140 ml/min) at the renal glomerular capillaries and delivered to the proximal tubules. The composition of this ultrafiltrate is identical to that of plasma except that it is virtually protein free. If body fluid volume and composition are to be maintained, this fluid must undergo considerable changes in volume and composition by reabsorption and secretion as it passes along the nephron.