digestive system, in the animal kingdom, a group of organs functioning in digestion and assimilation of food and elimination of wastes. Virtually all animals have a digestive system. In the vertebrates (phylum Chordata, subphylum Vertebrata) the digestive system is very complex. It consists of the gastrointestinal tract (gut), an extensive tube extending from the mouth to the anus, through which the swallowing, digestion, and assimilation of food and the elimination of waste products are accomplished.
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