ABSTRACT
The gastrointestinal tract has two major functions: processing of ingested food with a view to providing nourishment for the body and excretion of indigestible items from food and biliary secretion. These apparently simple tasks pose very significant problems:
• The challenge of maintaining forward propulsive movement of food ingested intermittently without overstressing any part of the intestine. This requires a storage organ (stomach), one-way valves (sphincters) to maintain controlled propulsive movement, and a complex interplay of neural and hormonal influences to control general and regional motility
• A variety of secretions to break down the various chemical components of food. As the conditions required for this are hostile to the body and the enzymes are potentially damaging to body tissues, protective barriers to prevent autodigestion and mechanisms for controlling secretion are required. This again is dependent on a number of neural and hormonal influences with stimulatory and inhibitory actions.
