ABSTRACT
INTRODUCTION TO NASAL STRUCTURE AND FUNCTION The nose is a structurally and functionally complex organ in the upper respiratory tract of mammalian species. It is the primary site of entry for inhaled air in the respiratory system and therefore has many important and diverse functions. The nose not only serves as the principal organ for the sense of smell (olfaction), but it also functions to efficiently filter, warm, and humidify the inhaled air (air conditioning) before it enters the more delicate distal airways and alveolar parenchyma in the lung (1). The nasal passages have been described as an efficient “scrubbing tower” for the respiratory tract because they effectively absorb water-soluble and reactive gases and vapors, trap inhaled particles, and metabolize airborne xenobiotics (2). With its role as an “air conditioner” and a “defender” of the lower respiratory tract, the nose may also be vulnerable to acute or chronic injury caused by exposure to airborne toxic or infectious agents. Many diseases afflict nasal airways and associated paranasal sinuses, including allergic rhinitis and chronic sinusitis. The majority of these conditions are a consequence of viral or bacterial infections, allergic reactions, or aging. However, exposure of humans to toxic agents may also cause or exacerbate certain nasal diseases. In recent years, there has been a marked increase in the study of nasal toxicology and in assessing the human risk of nasal injury from inhaled toxicants (3,4). When using animal toxicology studies to estimate the risks of nasal toxicants to human health, it is important to have a good working knowledge of comparative nasal structure and function. Comparative aspects of the mammalian nose that have special relevance to inhalation toxicology are highlighted in this brief review.
