Figure 1.

The ‘master controller’ role of the duodenum. There are multiple physiological processes involving long and short regulatory loops with primary sensors in the duodenum. Acidic chyme entering the duodenum (1) evokes local mucosal autocrine and paracrine mechanisms involved in epithelial defense, that is, safe handling and absorption of large amounts of gastric acid (2) and stimulates a series of additional actions (3) related to the luminal digestion of nutrients (4) including secretion of bile from gallbladder (a), production and release of pancreatic secretions (b), activation of the ‘duodenal brake’ that inhibits gastric emptying and acid secretion (c,d), and increases duodenal motility (e). There are also signaling pathways to the brain (f). Appropriate handling and response to molecules is based on specific sensory information of luminal contents.