Metabolism by the Tubules

Although renal physiologists traditionally list glomerular filtration, tubular reabsorption, and tubular secretion as the 3 basic renal processes, we cannot overlook metabolism by the tubular cells. For example, the tubular cells may extract organic nutrients from the glomerular filtrate or peritubular capillaries and metabolize them as dictated by the cells’ own nutrient requirements. In doing so, the renal cells are behaving no differently from any other cells in the body. In contrast, other metabolic transformations performed by the kidney are not directed toward its own nutritional requirements but rather toward altering the composition of the urine and plasma. The most important of these are the synthesis of ammonium from glutamine and the production of bicarbonate.