27.22 : Gastric Emptying

Gastric emptying occurs when the stomach gradually releases chyme into the duodenum. When the stomach is distended, it triggers the release of gastrin, a hormone that promotes gastric acid secretion to aid in digestion. Additionally, stomach distension contributes to peristaltic waves that propel gastric contents toward the pyloric region. The gastroenteric reflex, on the other hand, primarily stimulates peristalsis in the intestines, facilitating the movement of contents further along the digestive tract.

In the pyloric antrum, peristaltic waves thoroughly blend partially digested food with gastric secretions, forming chyme. The pyloric sphincter stays closed primarily, allowing only liquids and small particles to pass through. This forces bigger food particles back, a process known as retropulsion. Multiple rounds of retropulsion generate a back-and-forth pumping action that breaks down solids, releasing chyme into the duodenum.

The complete gastric emptying process usually takes about four hours, but it can be influenced by factors like the composition of the meal or intestinal hormones such as cholecystokinin. For example, a carbohydrate-rich chyme quickly leaves the stomach, whereas a fatty chyme takes longer to digest in the stomach and enter the duodenum. Gastric emptying is instead controlled by processes within the stomach and duodenum that regulate the gradual release of chyme.