The Respiratory Defense System PDF

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The Respiratory Defense System...

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The Respiratory Defense System Along much of the respiratory tract, mucous cells in the epithelium and mucous glands in the lamina propria produce a sticky mucus that bathes exposed surfaces. In the nasal cavity, cilia sweep that mucus and any trapped debris or microorganisms toward the pharynx. There it is swallowed and exposed to the acids and enzymes in the stomach. In the lower respiratory system, the cilia beat toward the pharynx, moving a carpet of mucus in that direction and cleaning the respiratory surfaces. This mechanism is the mucociliary escalator The Respiratory Defense System Along much of the respiratory tract, mucous cells in the epithelium and mucous glands in the lamina propria produce a sticky mucus that bathes exposed surfaces. In the nasal cavity, cilia sweep that mucus and any trapped debris or microorganisms toward the pharynx. There it is swallowed and exposed to the acids and enzymes in the stomach. In the lower respiratory system, the cilia beat toward the pharynx, moving a carpet of mucus in that direction and cleaning the respiratory surfaces. This mechanism is the mucociliary escalator, Large quantities of airborne particles may overload the respiratory defenses and produce a variety of illnesses. For example, irritants in the lining of the conducting passageways can provoke the formation of mucous plugs that block airflow and reduce pulmonary function. Damage to the epithelium in the affected area may allow irritants to enter the surrounding tissues of the lung. The irritants then produce local inflammation. Airborne irritants—such as those in cigarette smoke—are known to promote the development of lung cancer (p. 877). Aggressive pathogens can also overwhelm respiratory defenses. Tuberculosis (tū-ber-kyū-LŌ-sis), or TB, results from an infection of the lungs by the bacterium called Mycobacterium tuberculosis. Bacteria may colonize the respiratory passageways, the interstitial spaces, the alveoli, or a combination of the three. Signs and symptoms generally include coughing and chest pain, plus fever, night sweats, fatigue, and weight loss. In 1900, TB, then known as “consumption” (because its victims wasted away), was the leading cause of death. An estimated one-third of the world’s population is still infected with TB today. The respiratory defense system can also fail due to inherited congenital defects affecting mucus production or transport. For example, cystic fibrosis (CF) is the most common lethal inherited disease in individuals of Northern European descent. It occurs in 1 in 3200 Caucasian births. The respiratory mucosa in these individuals produces dense, viscous mucus that cannot be transported by the respiratory defense system. The mucociliary escalator stops working, leading to frequent infections. Mucus also blocks the smaller respiratory passageways, making breathing difficult. The average life span for people with CF who live into adulthood is 37 years....