Final answer:
The finger-shaped structures on the inner surface of the small intestine are called villi. They increase the surface area for nutrient absorption.
Step-by-step explanation:
The tiny finger-shaped structures that cover the inner surface of the small intestine are called villi. These folds greatly increase the surface area for absorption of nutrients. The absorptive cells that line the small intestine have microvilli, which are even smaller projections that further maximize the surface area. These microvilli constitute a brush border and have enzymes that help in the final digestion of carbohydrates and proteins. Therefore, it's the villi (and not the microvilli) that are the larger, visible structures you can see that line the small intestine and work efficiently to absorb nutrients and pass them into the bloodstream through blood vessels contained within each villus.