Which substances move through the villi walls into the blood vessels during nutrient absorption in the small intestine?

• A. Starch and glycogen
• B. Amino acids and monosaccharides
• C. Large proteins and triglycerides
• D. Bile salts and cellulose

Answer: (B)

Verified step by step guidance

1. Understand the function of the villi in the small intestine: Villi are small, finger-like projections that increase the surface area for absorption. They contain blood vessels and lacteals to transport absorbed nutrients.
2. Recall the process of digestion: Starch and glycogen are broken down into monosaccharides (e.g., glucose) by enzymes like amylase and maltase. Proteins are broken down into amino acids by enzymes like pepsin and trypsin.
3. Identify which substances are small enough to pass through the villi walls: Monosaccharides and amino acids are small molecules that can diffuse or be actively transported into the blood vessels within the villi.
4. Eliminate incorrect options: Large proteins and triglycerides are too large to be absorbed directly into the blood vessels. Instead, triglycerides are broken down into fatty acids and glycerol, which are absorbed into lacteals, not blood vessels. Bile salts and cellulose are not absorbed; bile salts aid in fat digestion, and cellulose is indigestible fiber.
5. Conclude that the substances absorbed into the blood vessels through the villi walls are amino acids and monosaccharides, as they are the end products of protein and carbohydrate digestion, respectively.