19. How are inhalation and
expiration carried out?

Gap-fill exercise

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The diaphragm (exclusive mammals)
and the muscles can contract
relax varying the of the
thorax ( compartment where the
are located). The of the
thorax forces inhalation or
.

When the thorax is increased an
pressure lower than
atmospheric pressure (external)
created and gases enter the
lungs. the thorax volume
lowered the internal rises
above the pressure and the
is expelled from lungs.