Bronchial asthma

Asthma is physiologically characterized by increased responsiveness of the trachea and bronchi
to various stimuli and by wide spread narrowing of the airways that changes in severity either
spontaneously or as a result of therapy
Impairment of airflow in bronchial asthma is caused by three bronchial abnormalities.
i. Contraction of airway smooth muscles
ii. Thickening of bronchial mucosa from edema and cellular infiltration
iii. Inspissations in the airway lumen of abnormally thick, viscid plugs of excessive mucus.

Pathogenesis
There are two types of bronchial asthma i.e extrinsic and intrinsic.
Extrinsic asthma is associated with history of allergies in childhood, family history of allergies,
hay fever, or elevated IgE.
Intrinsic asthma occurs in middle-aged subjects with no family history of allergies, negative skin
tests and normal serum IgE.
Immunologic model
Asthma is a disease mediated by reaginic (IgE) antibodies bound to mast cells in the airway
mucosa. But not all features of asthma can be accounted for by antigen-challenge model. Nonantigenic stimuli like viral infections, exercise, and cold air stimulate bronchial spasm.
In allergic asthma, the immediate phase, i.e the initial response to allergen provocation, occurs
abruptly and is due mainly to spasm of the bronchial muscle.Allergen interaction with mast cellfixed IgE release histamine, LTC4 and LTD4 which cause bronchial spasm.