Asthma-II: Pathophysiology and Classification

Asthma is a prevalent chronic respiratory condition marked by inflammation and hyperresponsiveness of the airways. Its pathophysiology involves complex interactions among inflammatory pathways, immune responses, and neural mechanisms.

Additionally, environmental and genetic factors play crucial roles in determining an individual's susceptibility to asthma and the severity of their condition.

Critical processes in asthma pathophysiology include:

1. Initiation of Airway Inflammation:
   1. Trigger Exposure: Exposure to allergens or irritants starts the inflammatory process.
   2. Immune Cell Activation: Exposure leads to the activation of critical immune cells, including mast cells, macrophages, eosinophils, neutrophils, T and B lymphocytes, and airway epithelial cells, which are crucial for initiating the immune response.
2. Allergic Response and IgE Production:
   1. IgE Antibodies: Allergen exposure in allergic asthma leads to the production of specific IgE antibodies.
   2. Mast Cell Sensitization: These IgE antibodies bind to mast cells, effectively sensitizing them for the allergic response.
3. Mast Cell Degranulation:
   1. Trigger Re-Exposure: Re-exposure to the allergen binds to IgE on mast cells.
   2. Inflammatory Mediators Release: This triggers the release of inflammatory mediators like histamine, cytokines (proteins that signal immune responses), leukotrienes, and prostaglandins, which play a crucial role in inflammation and allergic reactions.
4. Airway Inflammation and Bronchoconstriction:
   1. Immune Cell Infiltration: Attracts more eosinophils, lymphocytes, and neutrophils.
   2. Airway Narrowing: Results in bronchoconstriction, vascular congestion, edema, and mucus secretion.
5. Neural Control Alterations:
   1. Autonomic Nervous System: Involvement of sympathetic and parasympathetic systems.
   2. Increased Parasympathetic Activity: This leads to muscle contraction, mucus secretion, and bronchoconstriction.
6. Airway Remodeling:
   1. Chronic Inflammation Effects: Causes structural changes in the bronchial wall.
   2. Structural Changes: Include fibrosis, muscle hypertrophy, hyperplasia, mucus gland hypersecretion, inflammation, and angiogenesis.

In summary, asthma results from an exaggerated immune response in the airways, leading to inflammation, bronchoconstriction, and remodeling. These contribute to typical symptoms like wheezing, coughing, and shortness of breath. Asthma management involves medications targeting these mechanisms, and avoiding triggers.