Uptake and metabolism of toxicants in the respiratory tract.

The sites of uptake and retention of inhalants within the respiratory tract influence which tissues are susceptible to damage. Physical and chemical properties of inhalants, including size, water:air and oil:water partition coefficients, and reactivity or susceptibility to metabolism are the major factors that affect deposition and retention. The high metabolic capacity of the cells of the olfactory tissue and bronchiolar Clara cells contributes to their susceptibility to damage from both inhaled and bloodborne toxicants. The major enzymes that metabolize pesticides and many other potential toxicants are the cytochrome P450 and flavin-containing monooxygenases and the carboxylesterases.