In the kidney nephron, in which segment does the greatest proportion of mandatory water and solute reabsorption occur from the glomerular filtrate?

Answer and explanation

Correct answer: B. Proximal convoluted tubule

  1. Step 1: Trace renal filtration and tubular processing: Glomerular filtration produces approximately 180 liters of ultrafiltrate daily.
  2. Step 2: The proximal convoluted tubule (PCT) has extensive microvilli (brush border) and dense mitochondria.
  3. Step 3: The PCT obligatorily reabsorbs about 65-70% of filtered water, sodium, chloride, and 100% of filtered glucose and amino acids.
  4. Step 4: Identify the proximal convoluted tubule.
Answer
Proximal convoluted tubule.
Why not the others: 'Distal convoluted tubule' mediates selective, hormone-regulated (aldosterone) electrolyte reabsorption; 'Collecting duct' mediates facultative water reabsorption regulated by vasopressin (antidiuretic hormone); 'Ascending limb of loop of Henle' is impermeable to water while actively pumping solutes.

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