by Barnaby Meins

Created on: March 29, 2008

Asthma is a chronic inflammatory disorder of bronchi characterized by episodic, reversible bronchospasm resulting from an exaggerated bronchoconstrictor response to various stimuli. This is usually accompanied with excess mucus secretion which further constricts the airway. There are two main types of asthma, namely extrinsic and intrinsic asthma.

Intrinsic asthma is induced by aspirin, infections and other causes such as stress and exercise. Extrinsic asthma is an allergic response. Examples of allergens include pollen grains and dust mites.

Described is a summarized medical account of how extrinsic asthma comes about. When allergens such as pollen grains are present, the B cells in the body produce a unique antibody of type IgE. The IgE is then coated on the surface of the mast cells. These mast cells are found in various tissues and also found in the bronchi. When the patient is exposed to the allergen again, the cross linking of at least two IgE on the mast cells causes degranulation of the mast cells. This causes the release of inflammatory mediators, such as histamine, platelet activating factor and prostaglandin; causing inflammation, edema and smooth muscle contraction. The bronchial wall is thickened by plasma leakage and eosinophils (a kind of white blood cell) migrate from the blood into the bronchial wall. This causes the mucus glands to secrete excess mucus. This greatly reduces the airway and causes any constriction of the smooth muscle to further reduce the airway.

Asthma occurs about four to twelve hours after the first introduction to the allergen. Mediators allow the T-cells, eosinophils and basophils to enter and attach to the airway tissues. These cells then release mediators, narrowing the airway further. The parasympathetic nervous system causes bronchoconstriction via the release of acetylcholine. Inflammation also causes the leakage of proteins into the tissues. After the late response, the patient is very susceptible to future asthma attacks upon the exposure to the same allergen. As such, the patient should avoid going to places where there are a high chance of exposure to the allergen.

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