ABSTRACT
INTRODUCTION The nasal cavity provides several important respiratory defense mechanisms. It serves to condition the inspired air prior to its entry into the lower respiratory tract. In addition to heating and humidifying the airstream, the nasal cavity scrubs particulates and vapors from the airstream as well (chap. 6). These processes can be quite efficient; in the rodent upper respiratory tract deposition for particles greater than 5 m can exceed 80%. Essentially complete scrubbing (>95%) of water-soluble reactive vapors such as formaldehyde, acetic acid, or hydrogen fluoride occurs in the rodent nose (chap. 6) (1,2). Efficient scrubbing leads to high delivery of airborne toxicants to nasal tissues, making the nose an ideal site, from a dosimetric view, for detection of noxious airborne substances and initiation of appropriate reflex responses. The nasal cavity also provides important warning functions about the quality of the inspired air. Cranial nerve I, the olfactory nerve, is specialized for the detection of odors. Cranial nerve V, the trigeminal nerve, contains afferent sensory nerves that detect the presence of noxious materials. Several terms have been used to describe the trigeminal nerve detection of such materials, including nociception and chemesthesis (chap. 13).
