Comparative physiology of the mammalian colon and suggestions for animal models of human disorders.

The large intestine is absent from the digestive tract of some mammals and shows a considerable degree of gross structural variation among the other species. The cecum serves as the major site for digesta retention and microbial fermentation in lagomorphs, most rodents, and many herbivorous marsupials, but the proximal colon appears to serve this purpose in most other mammals. The VFA end-products of microbial fermentation play an important role in the normal secretory and absorptive processes of the colon. Among those species that have received the most extensive study, the pig appears to have a colon most similar to that of humans in its gross structural and absorptive characteristics.