The function of the respiratory tract of the pig is straightforward: gaseous exchange between inspired air and the blood. However, the cellular mechanisms by which this function occurs are complex and integrated with other bodily functions such as olfaction, deglutition, and phonation. Several features of the respiratory tract in the pig are unique. Most obvious are the shape of the nasal planum and the natural behavior of pigs to root the nose through dirt and surface materials such as feedstuffs, feces, and water. Many other features are similar to a wide cross section of mammals. The respiratory tract is composed of air passages through the nasal cavity, pharynx, and trachea that conduct and modify inspired air prior to entrance into the lung. Modifications of inspired air include warming and humidification of the air and filtering of particulate matter. The air also activates olfactory receptors in specialized epithelia of the nasal cavity. The flow of inspired air is altered during deglutition of saliva, solid materials, or liquid through contraction of the pharyngeal muscles and the larynx. Gaseous exchange of oxygen and carbon dioxide is the principal function of the lung and occurs deep in the parenchyma across the alveolar septa! wall. With expiration, air flow is reversed and ·pressures of the outflowing air through the laryngeal vocal folds produce phonation.