|Allergy and Asthma
Southwestern United States
||Information for patients with allergy and related
in the Southwest
Mechanisms of Respiratory Allergy
Causes of symptoms of allergic rhinitis (hay fever).
Symptoms of this problem are caused by a combination of
Causes of symptoms of asthma. Symptoms of asthma are caused
by excessive secretions in the bronchi, spasm of smooth muscle in the bronchial wall and
inflammatory swelling of the bronchial lining (mucosa). These changes cause
obstruction to airflow in and out of the lungs. The increased obstruction during
exhalation leads to shortness of breath, wheezing and trapping of air in the
chest. Cough is caused by increased airway secretions and airway inflammation.
Interaction of heredity and environment. The tendency to become allergic in individuals with allergic asthma is inherited. For example, over 50% of children whose parents both have allergic disease will also develop allergic disease. Allergy is controlled by several genes that influence production of IgE antibodies. Allergic disease develops only when a person becomes exposed to those allergens to which he has become sensitive due to genetic predisposition. There is increasing evidence to suggest that predisposition to respiratory allergy may also be increased by protection from bacterial exposure in early childhood (such as aggressive antibiotic therapy of respiratory infection, and avoidance of exposure to animals).
Mechanisms of bronchial irritability. A fundamental problem in asthma is irritability of bronchi caused by inflammation in the bronchial walls. The inflammation causes loss of protective epithelial cells from the mucosa (lining of the bronchial wall), exposing sensitive nerve endings to the irritating effects of chemical air pollutants and dry air. Predisposition to asthma is inherited, probably as the result of multiple genetic factors, some of which are independent of allergy-determining genes. Research suggests that genes that control various inflammatory mechanisms are important in causing allergic inflammation in the lung.
Relationships between allergy and bronchial irritability. Allergic reactions in the lungs cause inflammation during which inflammatory cells called eosinophils and lymphocytes are attracted to the bronchial tissues. Products from these cells cause damage to the bronchial lining, which in turn leads to bronchial irritability that may persist for several weeks after withdrawal from allergen exposure. This is most likely to occur when there is a delayed response to allergen known as a late phase reaction. Prolonged allergic inflammation in the bronchial walls may lead to thickening of the supportive membrane under the epithelial lining of the bronchial airways, and to a gradual and progressive loss of the ability of the airways to respond to a bronchodilator drug.
For additional information on how abnormalities of the immune system cause allergic
reactions, follow these links to the American Academy of Allergy Asthma and
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