Final answer:
The main roles of the small intestine are digestion and absorption. The small intestine has a folded surface with villi that increase the surface area for absorption. Epithelial cells in the villi absorb nutrients from digested food and release them into the bloodstream.
Step-by-step explanation:
The main roles of the small intestine are digestion and absorption. It is where the digestion of protein, fats, and carbohydrates is completed. T
he small intestine has a highly folded surface with finger-like projections called villi, which increase the surface area for absorption. The villi are lined with epithelial cells that absorb nutrients from digested food and release them into the bloodstream. The small intestine also produces intestinal juice, which further aids in digestion and absorption.