Pathogenesis of Asthma, and Its Macroscopic & Microscopic Presentation

Pathogenesis of Asthma, and Its Macroscopic & Microscopic Presentation

 What Is Asthma?

Asthma is a chronic inflammatory disease of the airways characterized by reversible airflow obstruction, bronchial hyperresponsiveness, and airway inflammation. It affects both children and adults and can be triggered by allergens, infections, exercise, or irritants.

 Pathogenesis of Asthma

The pathogenesis of asthma is complex and involves genetic, environmental, and immune system factors. Here is a step-by-step explanation:

1. Trigger Exposure

  • Common triggers: allergens (dust mites, pollen), respiratory infections, cold air, exercise, smoke, and pollution.

2. Immune System Activation

  • In atopic (allergic) asthma, exposure to allergens leads to activation of Th2 CD4+ T cells.

  • These Th2 cells release:

    • IL-4 promotes IgE production by B cells.

    • IL-5 activates eosinophils.

    • IL-13 promotes mucus secretion and IgE production.

3. Mast Cell Degranulation

  • IgE binds to mast cells, and on re-exposure, cross-linking leads to degranulation.

  • This releases histamine, leukotrienes, and prostaglandins, causing:

    • Bronchoconstriction

    • Vasodilation

    • Mucus production

4. Eosinophilic Inflammation

  • Eosinophils infiltrate the airway walls and release:

    • Major basic protein (MBP)

    • Eosinophilic cationic protein (ECP)

  • These cause epithelial damage, worsening inflammation.

5. Airway Remodeling (Chronic Asthma)

  • Repeated inflammation leads to:

    • Smooth muscle hypertrophy and hyperplasia

    • Goblet cell hyperplasia

    • Subepithelial fibrosis

    • Increased vascularity

Macroscopic Presentation of Asthmatic Lungs

During autopsy or gross examination, asthmatic lungs may show:

  • Hyperinflated lungs due to air trapping

  • Occlusion of bronchi and bronchioles by thick, tenacious mucus plugs

  • Areas of atelectasis (collapsed alveoli)

  • Mucoid impaction in the bronchi

 Microscopic (Histopathological) Presentation

Key microscopic features of asthma include:

1. Airway Inflammation

  • Eosinophilic infiltration in the mucosa and submucosa

  • Presence of mast cells, lymphocytes, and macrophages

2. Goblet Cell Hyperplasia

  • Increase in mucus-secreting cells in the bronchial epithelium

3. Mucus Plugging

  • Bronchial lumens filled with Curschmann spirals (mucus plugs with shed epithelial cells)

4. Charcot-Leyden Crystals

  • Needle-shaped crystals derived from eosinophil membrane proteins

5. Basement Membrane Thickening

  • Thickened subepithelial basement membrane due to collagen deposition

6. Smooth Muscle Hypertrophy

  • Increased thickness of bronchial smooth muscle

7. Subepithelial Fibrosis

  • Due to repeated injury and repair

 Summary

Feature Description
Disease Asthma
Pathogenesis Immune-mediated inflammation (Th2 dominant), mast cell activation, eosinophilic response
Macroscopic Features Hyperinflated lungs, mucus plugging, atelectasis
Microscopic Features Eosinophils, Curschmann spirals, Charcot-Leyden crystals, smooth muscle hypertrophy, goblet cell hyperplasia


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