Stevens, C. Edward College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina.
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A set of structures and organs in which food substances are digested. The vertebrate digestive system consists of the digestive tract (alimentary canal) and ancillary organs that serve for the acquisition of food and the assimilation of nutrients required for energy, growth, maintenance, and reproduction. Food is ingested, reduced to particles, mixed with digestive fluids and enzymes, and propelled through the digestive tract. Enzymes produced by the host animal and microbes indigenous to the digestive tract destroy harmful agents and convert food into a limited number of nutrients, which are selectively absorbed. Some characteristics of the vertebrate digestive system are common to all classes of vertebrates and appear to have been conserved in their evolution. In other aspects, the digestive systems of vertebrates show numerous structural and functional adaptations to their diet, habitat, and other physiological characteristics (Fig. 1). Carnivores, which feed exclusively on other animals, and species that feed on plant concentrates (seeds, fruit, nectar, and pollen) tend to have the shortest and simplest digestive tract. The digestive tract tends to be more complex in omnivores, which feed on both plants and animals, and most complex in herbivores, which feed principally on the fibrous portions of plants. See also: Adaptation (biology); Animal evolution; Energy metabolism; Enzyme; Food; Nutrition; Physiological ecology (animal)
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