63 Respiratory Integration of Systems

With the respiratory system’s constant interaction with our external environment it is considered a portal of entry for irritants and microorganisms. Protection of the body from these entering substances involves multiple forms of defense.

The epithelia of the upper respiratory tract contains goblet cells that produce mucus that lines the nasal cavity and most of the bronchial tree. The mucus helps to moisten the air and to trap microorganisms and particles. Mucus also contains immunoglobulin molecules which can bind pathogens and signal immune cells if needed. The cilia on respiratory epithelial cells of both the upper (above the larynx) and lower (below the larynx) respiratory tracts beat toward the pharynx creating the mucociliary elevator so that the mucus and trapped material can be swallowed. Swallowing delivers the microorganisms and particles to the stomach for destruction in stomach acid. Nerves and blood vessels underlie the epithelia in the nasal cavity. Sensory receptors can be stimulated by inhaled caustic material, resulting in the reflex called sneezing which rids these materials from the respiratory tract. At the level of the alveoli, phagocytic macrophages ‘patrol’ the lung tissues for invaders that have made it deeper into the respiratory system.