Final answer:
The muscularis externa is the layer responsible for segmentation and peristalsis in the digestive tract, having a key role in facilitating mechanical digestion and movement of food.
Step-by-step explanation:
The muscularis externa is responsible for segmentation and peristalsis in the gastrointestinal tract. This layer is made up of a double layer of smooth muscle: the inner circular layer and the outer longitudinal layer. The coordinated contractions of these muscles promote mechanical digestion and propulsion of food along the digestive tract.
Segmentation refers to the alternating contractions and relaxations of non-adjacent segments of the intestine that help in the mechanical breakdown of food and mixing with digestive juices. Peristalsis is the rhythmic contraction of muscles that propels food forward through the digestive system. Together, these processes are essential for the proper functioning of digestion and absorption of nutrients.