One example is that of your lungs. First, there is the epiglottis, a small trapdoor that blocks entry to the lungs when you swallow food. Coughing is a second line of lung defense. Third, there is a sticky escalator lining the route to your lungs whereby small invaders are trapped by mucus and removed by the upward movement of tiny bristles.

The last line of lung defense is scavenger white blood cells. These sanitary agents engulf harmful microscopic particles. Thanks to such mechanisms, our lungs keep working in safety.

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The epiglottis is one of many mechanisms that protect your lungs

Epiglottis open

Epiglottis closed

Trachea (windpipe)

Esophagus (food passage)