Biology / Unit 13 Bio 3155 short lesson, about 20 seconds
Negative-Pressure Breathing Mechanics
Captions available
The idea
Mammalian inhalation works by negative pressure: the diaphragm contracts and flattens, the chest cavity expands, and falling internal pressure draws air in, per the inverse pressure-volume relationship.
In practice
Diaphragm relaxation during exhalation shrinks the chest cavity, raising pressure and pushing air back out.
Where people slip
The lungs do not actively pull themselves open — they expand passively because chest-cavity pressure around them drops first.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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