- [Narrator] Breathe in, breathe out.
With every breath, the body
is replenished and cleansed.
A process made possible
by two of the body's most
important and delicate organs.
The lungs are two major components
of the respiratory system.
Soft, light, and elastic,
these organs are prime for taking in
and filling up with air.
Each lung is subdivided into
compartments called lobes.
The right lung has three,
and the left lung,
which is slightly smaller to accommodate
the positioning of the heart, has two.
This compartmentalization provides
a fail-safe for the lungs,
so that if one lobe is damaged,
the four other lobes may remain
intact and able to function.
The lobes are also connected
to separate branches,
called bronchi, of the trachea,
which delivers air from
the nose and mouth.
These branches provide the lobes
independent supplies of air.
Within each lobe,
the bronchi split off into
numerous smaller offshoots
that end in air sacs.
Known as alveoli,
these sacs are responsible
for a crucial exchange of air.
When a person inhales,
oxygen fills the alveoli.
The alveolar walls, which
contain countless capillaries,
are so thin that the oxygen
inhaled can pass through them
and be absorbed by blood
cells within the capillaries.
A similar transaction occurs
in the opposite direction.
Carbon dioxide waste
transported in the bloodstream
can pass through the alveolar walls.
From there, they are expelled
with every exhalation.
This exchange of gases,
known as respiration,
is what gives the
respiratory system its name.
Because of their intake of air,
the lungs are constantly
exposed to the elements,
and sometimes fall victim to them.
Lung conditions may
develop, such as emphysema,
which for some is caused by the
inhalation of tobacco smoke.
And pneumonia, which can be caused by
the inhalation of infectious organisms.
All together, these
and other lung diseases
are the fourth-leading cause
of death in the United States.
The lungs are delicate organs.
But despite their vulnerability,
their anatomical design
allows them to stay strong
and play a vital role in fueling the body.
