Final answer:
Villi and microvilli increase the internal surface area of the small intestine, enhancing the body's ability to absorb essential nutrients such as bile salts and vitamin B12. This structural adaptation allows for the efficient transfer of nutrients from the digestive system into the bloodstream.
Step-by-step explanation:
Villi and microvilli aid in absorption primarily by increasing the surface area of the small intestine. This increase in surface area is critical for maximizing the absorption of nutrients. Villi are folds in the lining of the small intestine, while microvilli are even smaller projections that extend from the cells on the surface of the villi. Together, they create a vast area for nutrient absorption. This is necessary for the efficient uptake of lipids, amino acids, sugars, vitamins such as bile salts and vitamin B12, and other nutrients from the chyme that moves through the small intestine. As nutrients are absorbed, they pass through the walls of the villi into the bloodstream, where they can be delivered to where they are needed in the body. When villi function is compromised, nutrient absorption is significantly reduced, which can lead to malnutrition and other health issues.