Which aspect of Fanconi syndrome is primarily affected?

Fanconi syndrome is a disorder of the renal proximal tubules, primarily impacting the kidneys' ability to reabsorb certain substances. The proximal tubules normally reabsorb approximately 65-70% of the filtered sodium and water, as well as nearly all glucose, amino acids, and bicarbonate. In Fanconi syndrome, the proximal tubular cells fail to reabsorb these substances properly, leading to renal wasting of glucose (glycosuria), amino acids (aminoaciduria), phosphate (phosphaturia), and bicarbonate (resulting in metabolic acidosis).

This dysfunctional reabsorption significantly impacts the composition of the urine and can lead to various metabolic sequelae. The other choices refer to different facets of kidney function: the glomerular filtration rate pertains to blood plasma filtration, distal tubular secretion focuses on the functions of the distal tubules, and Bowman's capsule is involved in the initial filtration of blood. However, none of these directly address the primary defect seen in Fanconi syndrome, which is specifically related to the proximal tubules' impaired reabsorption abilities.