A. ABSORPTION VS PRESYSTEMIC ELIMINATION 1 Toxicants may be eliminated as they move from the site of exposure to the systemic circulation. COMMON for CHEMICALS ABSORBED FROM THE GASTROINTESTINAL (GI) TRACT - they must first pass through the GI mucosal cells, liver, and lung before being distributed to the rest of the body by the systemic circulation. generally REDUCES THE TOXIC EFFECTS OF CHEMICALS that reach their target sites by way of the systemic circulation. - may CONTRIBUTE TO INJURY to these sites (digestive mucosa, liver, & lungs) 2 The __may eliminate a significant fraction of a toxicant during its passage through these tissues