How does the distal convoluted tubule differ histologically from the proximal tubule?

• A. Distal tubule cells are tall and highly eosinophilic with abundant microvilli
• B. Distal tubule cells are identical to proximal tubule
• C. Distal tubule cells are smaller, less eosinophilic, with fewer microvilli; distinct luminal border
• D. Distal tubule cells are glandular and secrete mucus

Answer: (C)

The distal convoluted tubule differs from the proximal tubule in its epithelial cell characteristics that reflect their different roles. Proximal tubule cells are tall and highly eosinophilic because they are packed with mitochondria and have a prominent brush border of microvilli, giving a fuzzy, brush-bordered apical surface. In contrast, distal tubule cells are smaller, have paler cytoplasm with fewer mitochondria, and possess far fewer microvilli, so the luminal border appears more distinct and smooth. This combination—smaller size, less eosinophilic cytoplasm, fewer microvilli, and a clearer luminal border—best describes the distal tubule.