In individuals with lactose intolerance, the enzyme lactase, responsible for lactose digestion, is typically located in which specific region of the gastrointestinal tract?
Brush-border of the small intestine
Brush-border of the large intestine
Lumen of the stomach
Hepatic cells of the liver
Lactase, the enzyme responsible for lactose digestion, is primarily located in the brush-border of the small intestine. The brush-border refers to the microvilli-covered surface of the intestinal epithelial cells. These microvilli increase the surface area available for nutrient absorption. Lactase is embedded in the brush-border membrane, where it acts to break down lactose into its component sugars, glucose and galactose. In individuals with lactose intolerance, the activity of lactase is reduced, leading to difficulties in digesting lactose-containing foods. Hence, the correct answer is option 1.