<Li> Motilin--is in the duodenum and increases the migrating myoelectric complex component of gastrointestinal motility and stimulates the production of pepsin . </Li> <P> Digestion is a complex process controlled by several factors . pH plays a crucial role in a normally functioning digestive tract . In the mouth, pharynx and esophagus, pH is typically about 6.8, very weakly acidic . Saliva controls pH in this region of the digestive tract . Salivary amylase is contained in saliva and starts the breakdown of carbohydrates into monosaccharides . Most digestive enzymes are sensitive to pH and will denature in a high or low pH environment . </P> <P> The stomach's high acidity inhibits the breakdown of carbohydrates within it . This acidity confers two benefits: it denatures proteins for further digestion in the small intestines, and provides non-specific immunity, damaging or eliminating various pathogens . </P> <P> In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes . The liver secretes bile into the duodenum to neutralize the acidic conditions from the stomach, and the pancreatic duct empties into the duodenum, adding bicarbonate to neutralize the acidic chyme, thus creating a neutral environment . The mucosal tissue of the small intestines is alkaline with a pH of about 8.5 . </P>

Where does the human chemical digestion of carbohydrates end