Lactose, a sugar found in milk, can only be digested by lactase, a brush border enzyme. All babies produce lactase, but only some adults do. Adults who do not produce lactase are referred to as lactose intolerant, as the presence of undigestible lactose can lead to uncomfortable digestive side effects such as gas and diarrhea. Based on your understanding of the small intestine, where would you expect to find the most lactase in babies and those adults that can digest lactose?

• A. Duodenum.
• B. Jejunum.
• C. Ileum.
• D. Cecum.

Answer: (B)

Verified step by step guidance

1. Understand that lactase is an enzyme located in the small intestine, specifically on the brush border of the intestinal lining.
2. Recall that the small intestine is divided into three main sections: the duodenum, jejunum, and ileum.
3. Recognize that the jejunum is the middle section of the small intestine and is primarily responsible for the absorption of nutrients, including sugars like lactose.
4. Consider that the presence of lactase is crucial for the digestion of lactose, and it is most active where nutrient absorption is highest, which is in the jejunum.
5. Conclude that the jejunum is the most likely location to find the highest concentration of lactase in both babies and adults who can digest lactose, due to its role in nutrient absorption.