Which feature best describes the brush border in intestinal epithelium?

• A. Dense microvilli that increase surface area for absorption.
• B. Cilia that move mucus along the intestinal surface.
• C. Keratinized protective layer.
• D. Basal lamina rich in collagen type IV.

Answer: (A)

The brush border is defined by a dense layer of microvilli on the apical surface of intestinal absorptive cells. These microvilli dramatically increase surface area, which is essential for efficient nutrient absorption. They also host brush border enzymes in their membranes, such as lactase, sucrase, and peptidases, enabling final digestion at the cell surface. The other features don’t describe the brush border: cilia are motile projections used to move mucus or fluid and are not the main feature of intestinal absorptive surfaces; a keratinized protective layer is a skin feature, not present in the intestinal lining; and the basal lamina is a basement membrane beneath the epithelium, not part of the apical brush border.