Parts of the Respiratory System
Figure 1 shows many of the structures of the respiratory system. Each of the parts has a
specific job. The parts of the respiratory system include:
Thediaphragmis a sheet of muscle that extends across the bottom of the rib cage. It
performs an important function in respiration. When the diaphragm contracts the chest
volume gets larger and the lungs take in air. When the diaphragm relaxes, the chest volume
gets smaller and air is pushed out of the lungs.
Thenose and nasal cavityfilters, warms, and moistens the inhaled air. The nose hairs
and mucus produced by the cells that line the nose catch airborne particles and prevent them
from reaching the lungs.
Behind the nasal cavity, air next passes through thepharynx,a long tube that is shared
with the digestive system. Both food and air pass through the pharynx. A flap of connective
tissue called theepiglottiscloses over the trachea when food is swallowed to prevent choking
or inhaling food.
Thelarynx,also called thevoicebox,is found just below the point at which the pharynx
splits into the trachea and the esophagus. Your voice comes from your larynx. Air from the
lungs passes across thin membranes in the larynx and produces sound.
Thetrachea,or wind pipe, is a long tube that leads down to the chest where it divides into
the right and leftbronchiin the lungs. The bronchi branch out into smaller bronchioles in
each lung.
The bronchioles lead to the alveoli.Alveoliare the little sacs at the end of the bronchioles.
They look like little bunches of grapes at the end of the bronchioles, as shown inFigure
19.2. Most of the gas exchange occurs in the alveoli. Gas exchangeis the movement of
oxygen across a membrane and into the blood and the movement of carbon dioxide out of
the blood.
How We Breathe
Most of the time, you breathe without thinking of it. Breathing is mostly an involuntary
action that is controlled by a part of your brain that also controls your heart beat. If you
swim, do yoga, or sing, you know you can also control your breathing.
Taking air into the body through the nose and mouth is calledinhalation.Pushing air out
of the body through the nose or mouth is calledexhalation. The man inFigure19.3is
exhaling before he surfaces in the pool water. The lungs cannot move by themselves. As
mentioned above, air moves into and out of the lungs by the movement of muscles. The
diaphragm and rib muscles contract and relax to move air in to and out of the lungs.
During inhalation, the diaphragm contracts and moves downward. The rib muscles contract