Where are lactase and maltase located, and what is their primary function in digestion?

• A. Brush Border Cells of the Small Intestine; Intraluminal Carbohydrate Digestion
• B. Gastric Mucosa of the Stomach; Lipid Digestion
• C. Pancreatic Acinar Cells; Protein Digestion
• D. Colonic Enterocytes; Bile Acid Absorption

Answer: (A)

Lactase and maltase are located on the brush border membrane of the small intestine’s absorptive enterocytes. Their primary job is intraluminal carbohydrate digestion: lactase hydrolyzes lactose into glucose and galactose, while maltase breaks maltose into two glucose molecules, allowing these monosaccharides to be absorbed. This localization and function distinguish them from enzymes in other tissues (for example, lipids digested by pancreatic enzymes or in the stomach) and explain why carbohydrate digestion is completed right at the intestinal surface before absorption.