BRAINCAKEProtecting the Lungs
Every breath brings dust, pollen, bacteria and viruses into the airways. The gas exchange system has several defences that stop these reaching and damaging the delicate alveoli.
• Nose: hairs filter out large particles, and the moist, well supplied lining warms and moistens incoming air so it does not dry out or cool the alveoli.
• Goblet cells in the epithelium of the trachea and bronchi secrete mucus. The sticky mucus traps particles and pathogens.
• Ciliated epithelial cells have hair-like cilia that beat in a coordinated wave, moving the mucus up and out of the airways to the throat, where it is swallowed. Stomach acid then destroys most of the trapped pathogens. This is sometimes called the mucociliary escalator.
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All 23 lessons in Gas Exchange · All Edexcel AS-level Biology topics