4. (windpipe) a tube about 12 to 15 cm (about 5
to 6 in) long located just below the larynx. The
trachea is formed of 15 to 20 C-shaped rings of
cartilage. The sturdy cartilage rings hold the trachea
open, enabling air to pass freely at all times
Here the trachea branches into two tubes, the
left and right bronchi, which delivers air to the left
and right lungs, respectively.
a narrow tube inside the lungs that
branches off the main air passages and connects it to
the alveoli.
The alveoli deliver oxygen to the circulatory
system and remove carbon dioxide.
- a large dome-shaped muscles that lies
just under the lungs

5. The flow of air in and out of the lungs is controlled by the
nervous system, which ensures that humans breathe in a
regular pattern and at a regular rate. Breathing is carried
out day and night by an unconscious process. It begins
with a cluster of nerve cells in the brain stem called the
respiratory center. These cells send simultaneous signals
to the diaphragm and rib muscles, the muscles involved
in inhalation. When the diaphragm is stimulated by a
nervous impulse, it flattens. The downward movement
of the diaphragm expands the volume of the cavity that
contains the lungs, the thoracic cavity. When the rib
muscles are stimulated, they also contract, pulling the rib
cage up and out. This movement also expands the
thoracic cavity. The increased volume of the thoracic
cavity causes air to rush into the lungs.

6. The nervous stimulation is brief, and when it
ceases, the diaphragm and rib muscles relax
and exhalation occurs. The rhythm set by the
respiratory center can be altered by conscious
control. The breathing pattern changes when a
person sings or whistles, for example. A person
also can alter the breathing pattern by holding
the breath. A person cannot hold the breath
indefinitely, however. If exhalation does not
occur, carbon dioxide accumulates in the blood,
which, in turn, causes the blood to become
more acidic.

8. What will happen if one part of the system fails
to carry out its function properly?
If the respiratory system’s tasks are
interrupted for more than a few minutes,
serious, irreversible damage to tissues occurs,
followed by the failure of all body systems,
and ultimately, death.

9. As we inhale, air travels to the lungs through a series
of air tubes and passages. It enters the body through
the nostrils or the mouth, passing down the throat to
the larynx, or voice box, and then to the trachea, or
windpipe. In the chest cavity the trachea divides into
two branches, called the right and left bronchi or
bronchial tubes, that enter the lungs. These bronchial
tubes splits to smaller and smaller branches called
bronchioles. The end of the bronchioles are tiny air sacs
called the alveoli, this is where the exchange of oxygen
and carbon dioxide happens in the body. In where the
oxygen is carried to the heart and pumped to the
different parts of the body and the carbon dioxide from
the blood is taken back to the lungs and exhaled.