Pulmonary Physiology, Metabolic & Defense Systems of the Lung, Dr. D. Penney

Table 13.01. Mechanisms that contribute to the defense of the respiratory tract.

A number of non-specific defense mechanisms exist to protect the lungs. These include clearance, secretions, and cellular and biochemical defenses. There are also specific defenses such as those antibody mediated and other cell-mediated mechanisms.

Clearance mechanisms include nasal clearance, tracheobronchial clearance, and alveolar clearance, ie. removal of objects at all levels of the pulmonary system.

Secretions include mucous, surfactant, lysozyme, interferon, and complement. Surfactant is a surface-active substance that decreases surface tension and prevents the alveoli from collapsing. Lysozyme is an enzyme (found in tears) that kills bacteria. Interferon and complement are players in the immune system.

Cellular defenses consist of phagocytic and non-phagocytic mechanisms. Phagocytes are cells such a macrophages that wander the pulmonary system engulfing and digesting foreign particles.

Biochemical defenses consist of antiproteolytic enzymes and antioxidants. Vitamin C, E and carotenoids are common antioxidants.

Specific defense mechanisms involves antibodies such as immunoglobulins. There is also cell-mediated mechanisms involving lymphocytes, etc.

Last Changed 04/28/00

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