ABSTRACT
The intensity of the effect of a toxicant on an organism is dependent primarily upon the relative effective concentration and the duration or persistence of the ultimate toxicant at a septic site of action. There are numerous portals of entry
for toxicants. The oral exposure route is the primary route of exposure to all substances including toxicants. In order to assess the potential adverse effects of toxicants by oral exposure, it is necessary to understand the structure, function, and mechanisms involved in the adsorption, distribution, metabolism/biotransformation, and excretion of toxicants that enter
Introduction ..............................................................................................................................................................................1521 Overview of the Gastrointestinal Tract ................................................................................................................................... 1522 Histological Organization of the Gastrointestinal Tract ......................................................................................................... 1523
Serosa ................................................................................................................................................................................. 1524 Muscularis .......................................................................................................................................................................... 1524 Submucosa ......................................................................................................................................................................... 1524 Mucosa ............................................................................................................................................................................... 1524 Cellular Absorption ............................................................................................................................................................ 1525
Digestive System Organization Overview .............................................................................................................................. 1527 Control of Digestive System Function ............................................................................................................................... 1527
Enteric Nervous System ................................................................................................................................................ 1527 Enteric Endocrine System ............................................................................................................................................. 1527
Mouth and Tongue ............................................................................................................................................................. 1528 Pharynx, Larynx, and Swallowing ..................................................................................................................................... 1528 Esophagus .......................................................................................................................................................................... 1530 Stomach ...............................................................................................................................................................................1531 Regulation of Gastric Secretion ..........................................................................................................................................1533 Small Intestine .....................................................................................................................................................................1533
