Definition
Bronchial asthma is a condition of the lungs which is characterized by periodic, reversible constriction (narrowing) of the bronchi. Why does constriction occur periodically? Constriction occurs because bronchi are hyperreactive to a variety of stimuli to which the patient is exposed intermittently.

Pathology
Why can't the patient breathe?

• Bronchi and bronchioles contain thick, tenacious mucous plugs. The mucous contains Curschmann's spirals, eosinophils and Charcot-Leyden crystals.
• Other characteristic histologic findings which lead to narrowing of the bronchus include: thickening of the basement membrane, submucosal edema, hypertrophy of the submucosal glands and smooth muscle cells. (Refer to Figure 15-14 in your textbook).

Pathogenesis

• Extrinsic or atopic asthma: This group is an example of type I IgE-mediated hypersensitivity reaction to foreign antigens. Begins in childhood. The child (his or her respiratory tract mast cells) is sensitized to a substance which is extrinsic to the body. A series of chemical and structural changes occur in the bronchi with exposure to the foreign substance. Clinical examples: pollen, food, animal dander. (Refer to Figure 15-13 in your textbook).
• Intrinsic or non-atopic: This group is an example of a non-immune reaction causing asthma. Clinical examples: aspirin, virus, stress, exercise.

Pathophysiology
Acute attack of dyspnea, prolonged coughing producing a large quantity of mucous, expiratory wheezing.