Respiratory System

The respiratory tract is a complex organ system both macroscopically and microscopically, with many different functions and cell types located throughout the nasopharyngeal, tracheobronchial, and pulmonary regions. Exposure to xenobiotics occurs via inhalation and via the blood following ingestion, dermal exposure, or parenteral administration. Potential toxic agents vary from inhaled particles and gases, to toxins in ingested food. Targeted toxicity of air- or blood-borne toxicants within the upper or lower respiratory tract is dependent on numerous factors, but most importantly the physical and chemical character of the chemical agent, site-specific tissue dosimetry and sensitivity, and host-dependent factors such as health status, gender and age. Knowledge of these factors is critical in interpreting the response to injury. In addition, species and strain differences (genetic factors) must be considered in interpretation of data to be used in risk assessment. In naturally occurring disease, the respiratory response to toxicant-induced injury is often nonspecific, so it is important to consider the gross distribution of respiratory lesions and to use detailed history and ancillary test results in conjunction with histological evaluation to determine potential etiologic agents.