What structure serves as the entry point from the stomach into the small intestine?

The pyloric sphincter is the structure that acts as the entry point from the stomach into the small intestine. It is a ring of smooth muscle located at the lower end of the stomach. The pyloric sphincter regulates the flow of partially digested food, known as chyme, from the stomach into the duodenum, which is the first part of the small intestine. This regulation is essential for proper digestion and absorption of nutrients, ensuring that the duodenum only receives chyme in manageable amounts, allowing for optimal processing and breakdown of food.

The function of the pyloric sphincter is crucial as it prevents backflow of intestinal contents into the stomach and helps in timing the release of gastric contents into the small intestine. In contrast, other structures mentioned, such as the duodenum, are parts of the small intestine itself and do not function as entry points; the esophagus transports food from the mouth to the stomach, and the cardiac sphincter (or lower esophageal sphincter) is located between the esophagus and the stomach, preventing reflux of stomach contents back into the esophagus.