Bronchial asthma is a chronic inflammatory disease of the airways characterized by reversible airway narrowing and increased airway responsiveness. It is one of the most common chronic diseases worldwide, affecting millions of people of all ages.
The pathogenesis of asthma is complex and involves a combination of genetic, environmental, and immunological factors. Asthma is typically triggered by allergens, such as pollen, dust, or pet dander, which cause the release of inflammatory mediators from mast cells and other immune cells in the airways.
These mediators, including histamine, leukotrienes, and cytokines, cause the constriction of the airways, increased mucus production, and inflammation of the airway wall. Over time, this inflammation can lead to structural changes in the airways, known as airway remodeling, which further contributes to the narrowing of the airways and the symptoms of asthma.
Pathophysiology of Asthma
The pathophysiology of asthma involves a complex interplay between the immune system, the airways, and the autonomic nervous system. The initial trigger for an asthma attack is often an allergen, which binds to specific receptors on mast cells in the airways.
Upon activation, mast cells release a variety of inflammatory mediators, including histamine, leukotrienes, and cytokines. These mediators cause the constriction of the airways, increased mucus production, and inflammation of the airway wall.
The inflammatory response in asthma is characterized by the infiltration of inflammatory cells, such as eosinophils, neutrophils, and lymphocytes, into the airways. These cells release additional inflammatory mediators, further contributing to the inflammation and narrowing of the airways.
Over time, the chronic inflammation in asthma can lead to structural changes in the airways, known as airway remodeling. Airway remodeling includes thickening of the airway wall, increased smooth muscle mass, and deposition of collagen and other extracellular matrix proteins.
Airway remodeling can further narrow the airways and make them more responsive to triggers, contributing to the symptoms of asthma.
Histology of Asthma
The histological features of asthma vary depending on the stage and severity of the disease. In early asthma, the airways may show mild inflammation with increased numbers of eosinophils and other inflammatory cells.
As the disease progresses, the airways may show more pronounced inflammation with thickening of the airway wall, increased smooth muscle mass, and deposition of collagen and other extracellular matrix proteins.
In severe asthma, the airways may be extensively remodeled, with significant narrowing and obliteration of the airway lumen.
Clinical Manifestations of Asthma
The clinical manifestations of asthma vary widely, depending on the severity of the disease. Common symptoms include:
- Wheezing
- Coughing
- Shortness of breath
- Chest tightness
Asthma attacks can be triggered by a variety of factors, including:
- Allergens
- Exercise
- Cold air
- Smoke
- Pollution
Asthma can be diagnosed based on a combination of symptoms, physical examination findings, and lung function tests.
Treatment of Asthma
The treatment of asthma is aimed at controlling symptoms, preventing exacerbations, and improving lung function. The mainstay of treatment is inhaled corticosteroids, which reduce inflammation in the airways.
Other medications used to treat asthma include:
- Bronchodilators, which relax the muscles in the airways
- Leukotriene modifiers, which block the action of leukotrienes, inflammatory mediators that contribute to asthma
- Immunomodulators
