Which structure forms the brush border to maximize absorptive surface area in the small intestine?

• A. Microvilli on simple columnar epithelium.
• B. Cilia on pseudostratified epithelium.
• C. Keratin on stratified squamous.
• D. Basal lamina.

Answer: (A)

Microvilli on the apical surface of simple columnar epithelial cells form the brush border. These tiny projections, supported by actin filaments, massively increase the surface area available for nutrient absorption and host enzymes that complete digestion. In the small intestine, absorptive enterocytes lining the villi display this brush border, making absorption highly efficient. Other options don’t fit: cilia on pseudostratified epithelium are for movement rather than absorption, keratin in stratified squamous provides protection, and the basal lamina is a basement membrane, not a surface for absorption.