Final answer:
The pyloric sphincter is the muscular valve at the lowest part of the stomach that controls the passage of food to the small intestine, with peristalsis being the rhythmic contractions that move food along the gastrointestinal tract.
Step-by-step explanation:
The hard muscular constriction at the lowest part of the stomach that leads to the small intestine is known as the pyloric sphincter. This sphincter acts as a valve to control the passage of partially digested food from the stomach to the small intestine. The muscularis mucosa helps create undulating folds in both the stomach and small intestine, which increases the surface area for digestion and absorption. The muscular layers in the small intestine, consisting of an inner circular layer and an outer longitudinal layer, work together to promote mechanical digestion and move food through the gastrointestinal tract using contractions known as peristalsis.
When the small intestine is ready to receive food, the pyloric sphincter relaxes, allowing the stomach contents to enter the small intestine for further digestion and nutrient absorption.