write:particles enter the upper portion of the bronchial tree muscle layers constrict the bronchi thus narrowing bronchial diameter and reducing the amount of particles entering the lu

particles enter the upper portion of the bronchial tree
muscle layers constrict the bronchi
thus narrowing bronchial diameter and reducing the amount of particles entering the lungs. The cough reflex
similar to the sneeze reflex
assists this process by eliminating particles trapped in mucus in the tracheobronchial region. Cilia that line the tracheobronchial region clean airways by propelling mucus and particles upward where they are removed by coughing and expectoration or swallowing. In the latter way
some particulate-phase pollutants may enter the gastrointestinal system. Despite these defense mechanisms
many fine particles and some relatively insoluble gases enter pulmonary tissue. Within the alveoli and bronchioles of the pulmonary region
specialized cells called phagocytes and macrophages ingest deposited matter (phagocytes and macrophages
derived from white blood cells
consume bacteria
and other particles and
as a result
serve as a pulmonary defense mechanism). These phagocytes and the matter they contain are normally transported out of the lungs in mucus by the cilia. However
they may also move through the alveolar membrane and enter either the lymphatic or circulatory system. Additionally
soluble components deposited in the alveoli may be absorbed by adjacent tissue and enter the lymphatic or circulatory system without being phagocytized. Although these mechanisms affect clearance from the respiratory system
they may expose other body systems to toxic materials. They may also result in tissue damage when phagocytes are destroyed and spill their contents when attempting to ingest toxic particles. Air Pollution and Respiratory Disease Community air pollution has been implicated as a causal or aggravating agent in diseases of the respiratory system such as chronic bronchitis
pulmonary emphysema
lung cancer
bronchial asthma
and infections. Chronic Bronchitis Bronchitis is a respiratory disease characterized by inflammation of the membrane lining bronchial airways. Bronchitis may be caused by pathogenic infections or respiratory irritants
those that occur in cigarette smoke
industrial exposures
and ambient and indoor air pollution. When bronchial inflammation persists for 3 months or longer
it is classified as chronic bronchitis. Extended irritation of the bronchial membrane is the primary cause of chronic bronchitis. It is characterized by a persistent cough and excessive mucus or sputum production
often accompanied by destruction of cilia and thickening of bronchial epithelium. Chronic bronchitis significantly affects respiratory function
as airway resistance is increased by occlusion of the bronchi
swelling of the inflamed membrane
and concomitant excess mucus production. Consequently
persons afflicted with the disease have difficulty breathing. Severe cases of chronic bronchitis are often followed by development of pulmonary emphysema. Combined chronic bronchitis and pulmonary emphysema are usually Air quality 164


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