Final answer:
The small intestinal wall has three features that increase its absorption surface area: circular folds, villi, and microvilli.
Step-by-step explanation:
The small intestinal wall has several specific features that aid in absorption. These include circular folds, villi, and microvilli. Circular folds are large folds in the mucosa and submucosa that increase the surface area. Villi are finger-like projections that cover the circular folds and further increase the surface area. Microvilli are hair-like projections on the surface of the epithelial cells that line the villi, and they further increase the surface area for absorption.