Digestive system Gastrointestinal tract

All of the organ systems in the body, except the reproductive system, contribute to the maintenance of homeostasis (see Table 1.1). For example, the gastrointestinal tract digests foods to provide nutrients to the body. The respiratory system obtains oxygen and eliminates carbon dioxide. The circulatory system transports all of these materials and others from one part of the body to another. The renal system eliminates wastes and plays a role in regulating blood volume and blood pressure. 

The parasympathetic system is designed to function more or less on an organ system basis, usually under conditions of minimal stress. For example, the activation of the gastrointestinal tract takes place during digestion of a meal constriction of the pupil and accommodation for near vision are essential for reading. 

Before reaching the systemic circulation, polyphenols orally administered will transit by the gastrointestinal tract (GIT) where they will be submitted to different biological and physiological parameters, which will participate to their bioavailability, such as the pH, the digestive enzymes, or the microflora. 

Figure 6.1 Anatomy of the human gastrointestinal tract. From V.C.Scanlon and T.Sanders (1995) The digestive system. Essentials of Anatomy and Physiology, F.A. Davis Company, Philadelphia, pp. 358-385...

Because of rich buccal vascularity, drugs delivered by the buccal route gain direct access to the systemic circulation and are not subject to first-pass metabolism. Also, therapeutic agents do not come in contact with the acidic digestive fluids secreted by the gastrointestinal tract. 

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