Final answer:
One way movement of materials in the GI tract is ensured by peristalsis, which involves wave-like contractions of smooth muscles that propel food through the gastrointestinal tract.
Step-by-step explanation:
One way movement of materials in the GI tract is ensured by peristalsis. This process involves rapid, involuntary, wave-like contractions of smooth muscles that move food through the gastrointestinal tract. The muscles in the walls of the GI tract generate these contractions, which occur sequentially, propelling the contents forward and preventing them from moving backward. The food is mixed and churned in the stomach, creating a semi-liquid mixture known as chyme. Then, peristalsis continues to move the chyme through the small and large intestines, where further digestion and absorption occur.
Finger-like projections called villi and microvilli, located in the small intestine, greatly increase the surface area for absorption, but their effectiveness is largely dependent on the movement generated by peristalsis which ensures that nutrients come into contact with these structures. Motility complexes and hormones like motilin also play roles in regulating the movement of chyme, contributing to the effectiveness of peristalsis.