The gastrointestinal tract (lat. gaster = stomach, intestinum = intestine) is the main part of the digestive system. It comprises the stomach, the small and the large intestine. The enzymatic brek-down of food, the resorption of nutrients and water as well as the excretion of undigestable or unusable components takes place in the gastrointestinal tract. Apart from enzymes, many bacteria take part in digestion; they are comprised by the term enteric flora. Apart from the gastrointestinal tract, the oral cavity where mechanical break-down takes place, the salivary glands (with digestive enzymes) and the esophagus, that serves to conduce food to the stomach. Visible are: esophagus, gaster, duodenum, jejunum, ileum, caecum, and colon.