Does gravity play a role in the passage of food through the GI tract?
The major functions of the digestive tract are usually summarized in two words – digestion and absorption. However, many of its specific activities, such as smooth muscle activity, and some regulatory events are not really covered by either term. The essential activities of the GI tract include the following six processes: • Ingestion – Food must be placed into the mouth before it can be acted on. This is an active, voluntary process. Once food is placed in the mouth, both mechanical and chemical digestion begin. First food is physically broken down by chewing. Then, as the food is mixed with saliva, salivary amylase begins the chemical digestion of starch, breaking it down into maltose. Saliva is normally secreted continuously to keep the mouth moist, but when food enters the mouth, much larger amounts of saliva pour out. The pressure of chewing increases the flow of saliva, as do some emotional stimuli. • Propulsion – If foods are to be processed by more than one digestive organ, the
