Which structural adaptation of the small intestine most effectively increases its surface area for nutrient absorption?

• A. A thick layer of smooth muscle in the intestinal wall
• B. The presence of villi and microvilli lining the intestinal wall
• C. The presence of a mucus layer covering the epithelium
• D. The secretion of digestive enzymes by the pancreas

Answer: (B)

Verified step by step guidance

1. Understand the function of the small intestine: The small intestine is the primary site for nutrient absorption in the digestive system. Its structure is adapted to maximize surface area for efficient absorption.
2. Identify the structural adaptations: The small intestine has villi (finger-like projections) and microvilli (tiny hair-like structures on the epithelial cells of the villi). These structures significantly increase the surface area available for nutrient absorption.
3. Compare the options: Evaluate each option provided in the question. A thick layer of smooth muscle aids in peristalsis but does not increase surface area. A mucus layer protects the epithelium but does not contribute to absorption. Digestive enzymes from the pancreas assist in breaking down food but are not structural adaptations of the small intestine.
4. Focus on the correct adaptation: The presence of villi and microvilli is the most effective structural adaptation for increasing surface area, as they provide a large interface for nutrients to be absorbed into the bloodstream.
5. Conclude the reasoning: The correct answer is the presence of villi and microvilli lining the intestinal wall, as these structures are specifically designed to enhance nutrient absorption by increasing the surface area.