Functional Evolution of Gastrointestinal Hormones

Abstract

The gastrointestinal tracts of vertebrates are useful systems in which to study the functional evolution of chemical regulatory systems because they provide a rich substrate of anatomical and physiological variability upon which selection pressures may act. The physiological problem of acquiring food and rendering it usable by incorporating it into the body of the organism is fundamental to all forms of life. Food is not available for nutrition until it has been absorbed across the wall of the intestine and enters the circulatory system. Topographically, food in the intestinal lumen is outside of the body. Vertebrates, including primitive fishes, have evolved systems for ensuring that ingested foods are processed efficiently in the various regions of the gut so that they are available at the appropriate times, in the appropriate gut segments, and in the appropriate chemical and physical forms to be absorbed and serve as the nutrients required for supporting the metabolic and behavioral activities of the organism.