Gastrointestinal tract

The gastrointestinal tract (also called the GI tract, digestive tract, and the alimentary canal) is the part of an animal that digests food and drink. For the human organs, see digestive system.

The canal (or tube) carries food through digestion and excretion. Into the tube come various digestive enzymes. Gut flora  help digestion, and the production of vitamins. Muscular movements pass the material down the tube. The gut usually has an exit, the anus, by which the animal disposes of solid wastes. Some small animals have no anus and dispose of solid wastes by other means, for example through the mouth.Ruppert E.E., Fox R.S. and Barnes R.D. 2004. Invertebrate zoology. 7th ed, Brooks/Cole. 

 Evolutionary history 
The gut evolved at least twice, an example of convergent evolution. Protostomes develop their mouths first, while deuterostomes develop their mouths second. Protostome include arthropods, molluscs, and annelids, and deuterostomes include echinoderms and chordates, including humans.

References

Category:Anatomy of the digestive system
Category:Animal anatomy