Asthma primarily affects which part of the respiratory system?

The correct option is Bronchi and bronchioles.

Step-by-Step Explanation:

1. What is Asthma?
Asthma is a chronic inflammatory disorder of the airways. It causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night or early in the morning.

2. Primary Site of Affection:
The respiratory tract consists of several structures, including the trachea, bronchi, bronchioles, and alveoli. Asthma primarily affects the bronchi and bronchioles, which are the conducting tubes that carry air into and out of the lungs.

3. Pathophysiology:
When a person with asthma encounters a trigger (such as allergens, cold air, or exercise), the smooth muscles surrounding the bronchi and bronchioles contract (bronchospasm). Additionally, the inner lining of these airways becomes inflamed and swollen, producing excess mucus. This narrows the lumen of the airways, making it difficult for air to pass through.

4. Roles of Other Structures:
- Diaphragm: The main muscle of respiration, involved in breathing mechanics rather than chronic airway inflammation.
- Trachea: The main windpipe leading down to the bronchi; while involved in air conduction, it is not the primary site of asthmatic airway hyper-reactivity.
- Alveoli: The tiny air sacs where gas exchange occurs, primarily affected by conditions like emphysema or pneumonia rather than classic asthma.

Therefore, asthma primarily affects the bronchi and bronchioles.