| The mechanical and anatomical basis of digestion
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| There is a purely mechanical component to digestion. Mastication (chewing) and preliminary digestion of food take place in the mouth. The food is then transferred into the esophagus in a process driven by the esophageal reflex. As the ever smaller particles appear in different parts of the GI tract, such as stomach and then duodenum, they themselves trigger peristalsis, which helps mixing and stimulates the secretory function. The major stimulator of peristalsis is the parasympathetic system.
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| Stomach and intestine have invaginated surfaces which multiply their surface area. The small intestine contains mucosal folds, intestinal villi, and microvilli making it the main absorptive surface.
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| page 113 |  | | page 114 |
| Figure 9.1 GI tract indicating multiple organ nature and function. The gastrointestinal (GI) tract includes several organs and functions. FFA, free fatty acids. |
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