ABSTRACT
This chapter describes the roles of the specialised areas of the gastrointestinal tract, together with associated specialised organs, in digestion. The digestive system is the pathway through which food is taken into the body and converted to base substances to ensure the body’s ongoing optimal functioning before eliminating anything not required. Digestion begins before food enters the system. The ‘cephalic phase’ is the phase of gastric secretion before food enters the stomach. Food enters the mouth and mechanical digestion of the food, especially hard foods, starts with the action of chewing. Mixing food with digestive secretions in the stomach effectively liquefies it to the consistency of a gruel or thick soup, and this is aided by peristaltic waves of muscle contraction. The interval between eating food materials and the time when the food residues are discharged from the body as faeces varies widely depending on individual characteristics and the diet consumed, and may vary day to day.
