Asthma is a chronic condition that affects the bronchial tubes, the air passages that carry air in and out of the lungs. During normal breathing, these tubes stay open so oxygen can enter the body and carbon dioxide can leave. In asthma, the airways can become inflamed, swollen, and narrowed, making breathing harder.
Understanding asthma helps students see how structure and function are connected in the respiratory system.
Key Facts
- Normal airway: open passage, relaxed smooth muscle, thin lining, and little mucus.
- Asthma airway: narrowed passage, tightened smooth muscle, swollen lining, and extra mucus.
- Airflow decreases when airway radius decreases because resistance rises sharply.
- Airway resistance is related to 1/r^4, so small narrowing can greatly reduce airflow.
- Common asthma triggers include pollen, dust, smoke, exercise, cold air, respiratory infections, and strong odors.
- Quick-relief inhalers often contain bronchodilators that relax smooth muscle and help open the airways.
Vocabulary
- Bronchial tube
- A branching airway that carries air between the trachea and the smaller air passages inside the lungs.
- Inflammation
- A protective body response that can cause swelling, redness, heat, and irritation in tissues.
- Mucus
- A sticky fluid made by airway lining cells that traps particles but can block airflow when too much is produced.
- Bronchoconstriction
- The tightening of smooth muscle around the airways, which makes the airway opening smaller.
- Bronchodilator
- A medicine that relaxes airway smooth muscle so the bronchial tubes can widen.
Common Mistakes to Avoid
- Thinking asthma is only a problem during an attack. Asthma involves long-term airway sensitivity and inflammation, even when a person feels well.
- Assuming mucus is the only reason breathing becomes difficult. Swelling of the airway lining and tightening of smooth muscle also narrow the passage.
- Ignoring early symptoms such as wheezing, coughing, or chest tightness. These signs can show that airways are narrowing before breathing becomes severely limited.
- Using a quick-relief inhaler as a replacement for all asthma care. Quick-relief medicine can open airways fast, but some people also need controller medicine to reduce inflammation over time.
Practice Questions
- 1 A student normally breathes 16 times per minute. During an asthma flare, the student breathes 24 times per minute. By what percent did the breathing rate increase?
- 2 In a simplified airway model, an airway radius decreases from 4 mm to 2 mm. Using airway resistance proportional to 1/r^4, how many times greater is the resistance after narrowing?
- 3 Explain why a quick-relief inhaler can make breathing easier during an asthma attack, but may not remove the original trigger such as pollen or cold air.