During a fast, a brief phase of intense sequential contractions begins in the stomach and gradually migrates to the ileum. Release of which of the following intestinal hormones is most likely responsible for this observed effect?
Motilin is a hormone released by the small intestine during the fasting state. Its waxing and waning blood levels correlate with the initiation and ending of migrating motor complexes (MMC). Fuhermore, injection of motilin has been shown to evoke MMC activity. The MMC typically begins in the stomach, and over a 90-120 minute period, migrates to the ileum, where it dies out. As one complex dies out in the ileum, another complex begins in the stomach provided the fasting state continues. Eating a meal interrupts the MMC activity. Cholecystokinin is released during the intestinal phase of the digestive period (not during a fast). Its secretion is evoked by the presence of fat and protein digestion products in the duodenum. It induces contraction of the gallbladder and relaxation of the sphincter of Oddi. Gastrin is released from G cells in the antrum, mostly during the gastric phase of the digestive period (not during a fast). It tends to increase stomach motility, although the rate of emptying is decreased because gastrin also causes the pyloric sphincter to contract. It also may contribute to the increase in ileal and colonic motility as pa of the gastroileal and gastrocolic reflexes, respectively. Gastrin-releasing peptide mediates the neural release of gastrin. Antral enteric neurons that are activated by vagal efferents or by local reflexes release gastrin-releasing peptide, which stimulates the G cells to secrete gastrin.
Cholecystokinin
Gastrin
Gastrin-releasing peptide
Motilin