Asthma - Role of Pollutants
Asthma is related to air pollution. The human body does possess intricate protective mechanisms. The hair in the nasal cavity, acts as a barricade to inhaled dust particles. The mucus covering of the nasal and pharyngeal mucosa traps most of the air pollutants; hence throat clearing, nose blowing, and sneezing are more common in the presence of dusty air. These are natural protective reflexes that clear the load of polluting particles from the nose and throat and make this important barrier useful for protecting our lungs. Our tonsils, which consist of lymphatic tissue, are strategically positioned in the pharynx to assist the defense system of the upper respiratory tract. Constant exposure to pollutants, including bacteria and viruses that pass through the throat with air, drink and food renders the tonsils susceptible to infections. This fact often prompts surgical removal of tonsils, and this procedure, unfortunately, removes an important protective barrier against pollutants entering our body. We don't prefer this attempt as it is just like removing the soldiers from the border to invite the enemies (bacteria etc.) to enter freely.
Further down in the bronchial tree, the inhaled air is continuously screened and the presence of residual pollutants triggers the cough reflex initiated by a constriction of the air passages. This airway constriction facilitates slower airflow, preventing the polluted air from entering the alveoli (terminal structures in the lungs where the exchange of oxygen occurs). In response, we cough to force down the air (regardless of its quality) to the alveoli. This explains why coughing is not the healthy reflex of clearing something out of lungs, but rather a desperate attempt to breathe, which simultaneously forces the polluted air into the lungs. Coughing is therefore an important signal of distress from the lungs, very much like indigestion is a sign of distress from the digestive tract. Coughing along with sneezing often precedes an asthma attack and the related condition, "allergic rhinitis."
Fortunately, the polluting particles that sneak into the lower respiratory tract are flushed off by epithelial cilia (a microscopic hairlike structure) towards pharynx. These epithelial cells are covered with a layer of mucus, which traps the polluting particles and carries them out to the throat. But in an asthmatic patient due to a chronic, inflammatory condition, the movement of ciliae is brought almost to a standstill, and the abnormally, increased secretion of mucus makes airway passages obstructed for air that we breathe.
Another rapid reaction system in our lungs to counteract pollution is made of various immune cells (or body defence cells), which literally devour the foreign particles. These cells collectively are called white cells and by their function are referred to as mactophages the cells that eat foreign matter. However, the action of white cells comes often at considerable Cost to the airways themselves. When macrophages ingest large amounts of the substances contained in a cigarette smoke, or silica or asbestos particles of polluted air, they release enzymes (intended to digest the invader, i.e., antigen), which cause the inflammation of the airways and chronic, nagging cough. This is in fact a classic mechanism of a chronic inflammatory and degenerative condition of the bronchial tree, often referred to as bronchitis and too often initiating the deadly disease of emphysema. The current view of asthma is that it is "a chronic inflammatory disorder in which many white cells play a role, especially mast cells, eosinophils and Tlymphocytes".
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