Knowledge of factors affecting the behavior and fate of inhaled particulate matter is of fundamental importance to the scientific disciplines of inhalation toxicology and aerosol therapy. Since particles are entrained and transported by airstreams, flow fields exert a great influence upon the deposition patterns of toxic substances and pharmacologic drugs within the human lung. In a series of independent works, (1-3)Martonen et al. have documented the effects of distinct morphological features of airways upon lung fluid dynamics. Herein, those systematic investigations are integrated into a cohesive view of the motion of inhaled air. As a direct result, improved surrogates of the human lung can be developed. Specifically, it is established that the following elements must be included in future experimental and theoretical models describing airway conditions and particle dosimetry: laryngeal effects, cartilaginous rings and carinal ridges. If these factors ace included such laboratory and mathematical models can become more physiologically realistic and be important components of future risk assessment and medical protocols.