What is the brush border composed of?

• A. Goblet cells
• B. Mitochondria
• C. Villi
• D. Microvilli

Answer: (D)

Microvilli are the tiny, finger-like projections on the apical surface of absorptive epithelial cells, such as those lining the small intestine. The brush border is formed by these microvilli, dramatically increasing the cell surface area available for nutrient absorption and hosting digestive enzymes right at the membrane to aid digestion. Goblet cells secrete mucus and are part of the epithelial layer, but they don’t contribute to the brush border’s surface texture. Mitochondria are energy-producing organelles inside cells and aren’t the structural component of the brush border. Villi are larger, multilayered folds of mucosa that enhance surface area at a tissue level, but the specific brush-border surface is made up of microvilli.