Final answer:
Segmentation is the mechanical digestive movement unique to the small intestine that enhances nutrient absorption by mixing chyme with digestive juices. The small intestine's villi and microvilli increase the surface area for efficient nutrient uptake.
D is correct
Step-by-step explanation:
The process that occurs only in the small intestine to increase the absorption of food and nutrients by mixing food is called segmentation. This is a unique mechanical digestive movement where chyme is moved back and forth, which increases the mixing of the chyme with digestive juices, thereby improving the opportunities for nutrient absorption. The small intestine is equipped with structural adaptations like circular folds, villi, and microvilli that significantly increase the mucosal surface area, enhancing the efficiency of nutrient absorption.
Villi are finger-like projections that line the small intestine, and each villus has many microscopic projections called microvilli. These structures expand the surface area available for absorption. During the process of absorption, nutrients pass from the digested food into the bloodstream or lymph system to be circulated throughout the body. Any material not absorbed into the bloodstream is moved towards the large intestine for eventual elimination from the body.