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How does the pylorus control the movement of chyme into the duodenum?

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Diagram of the human digestive system viewed from the front, showing and labeling organs including the mouth, teeth, tongue, salivary glands, pharynx, esophagus, liver, stomach, gallbladder, pancreas, large intestine, small intestine, appendix, rectum, and anus. — digestion The human digestive system as seen from the front.

The pylorus regulates the movement of chyme into the duodenum through the action of the pyloric sphincter, a ring of thickened circular muscle.12

This sphincter functions as a gatekeeper, remaining in a relaxed or open state for approximately two-thirds of the time to allow small quantities of well-emulsified food to pass into the small intestine. Because the opening is relatively narrow, it restricts the passage of large food particles or undigested material.1

The control mechanism is responsive to pressure: as the duodenum fills, the resulting increase in pressure triggers the pyloric sphincter to contract and close, preventing the backflow of intestinal contents into the stomach. Once the sphincter is closed, peristaltic waves in the duodenum further move the contents deeper into the digestive tract. By periodically discharging chyme only when its physical and chemical condition is suitable, the pylorus ensures that the digestive process proceeds efficiently.123