The Respiratory System
orously when we yell. Te muscles of the chest, abdomen, and
back provide the power for the airstream.
Te vocal folds actually produce buzzing sounds. Te per-
ceived quality of the voice depends on the coordinated activity
of many structures above the glottis. For example, the entire
length of the pharynx acts as a resonating chamber, to amplify
and enhance the sound quality. Te oral, nasal, and sinus cavi-
ties also contribute to vocal resonance. In addition, good enun-
ciation depends on muscles in the pharynx, tongue, so± palate,
and lips that “shape” sound into recognizable consonants and
Inﬂammation of the vocal folds, or
, causes the vocal
folds to swell, interfering with their vibration. Tis changes the
vocal tone, causing hoarseness, or in severe cases limiting us to a
whisper. Laryngitis is most o±en caused by viral infections, but
may also be due to overusing the voice, very dry air, bacterial
infections, tumors on the vocal folds, or inhalation of irritating
Sphincter Functions of the Larynx
Under certain conditions, the vocal folds act as a sphincter that
prevents air passage. During abdominal straining associated
with defecation, the glottis closes to prevent exhalation and
the abdominal muscles contract, causing the intra-abdominal
pressure to rise. Tese events, collectively known as
, help empty the rectum and can also splint (stabilize)
the body trunk when li±ing a heavy load.
, descends from the larynx
through the neck and into the mediastinum. It ends by divid-
ing into the two main bronchi at midthorax (see Figure 22.1). In
humans, it is 10–12 cm (about 4 inches) long and 2 cm (3/4 inch)
in diameter, and very ﬂexible and mobile. Interestingly, early
anatomists mistook the trachea for a rough-walled artery (
Te tracheal wall consists of several layers that are common
to many tubular body organs—the
—plus a layer of hyaline cartilage
has the same goblet cell–containing pseudostratiﬁed
epithelium that occurs throughout most of the respiratory tract.
Its cilia continually propel debris-laden mucus toward the phar-
ynx. Tis epithelium rests on a fairly thick lamina propria that
has a rich supply of elastic ﬁbers.
Smoking inhibits and ultimately destroys cilia. Without ciliary
activity, coughing is the only way to prevent mucus from ac-
cumulating in the lungs. For this reason, smokers with respira-
tory congestion should avoid medications that inhibit the cough
, a connective tissue layer deep to the mu-
cosa, contains seromucous glands that help produce the mucus
“sheets” within the trachea. Te submucosa is supported by 16
to 20 C-shaped rings of hyaline cartilage encased by the
, the outermost layer of connective tissue (Figure 22.6).
Te trachea’s elastic elements make it ﬂexible enough to stretch
and move inferiorly during inspiration and recoil during expira-
tion, but the cartilage rings prevent it from collapsing and keep
the airway patent despite the pressure changes that occur during
breathing. Te open posterior parts of the cartilage rings, which
abut the esophagus (Figure 22.6a), are connected by smooth
muscle ﬁbers of the
and by so± connective tissue. Be-
cause this portion of the tracheal wall is ﬂexible, the esophagus
can expand anteriorly as swallowed food passes through it.
Contraction of the trachealis muscle decreases the trachea’s
diameter, causing expired air to rush upward from the lungs
with greater force. Tis action helps expel mucus from the tra-
chea when we cough by accelerating the exhaled air to speeds
of 100 mph!
Te last tracheal cartilage is expanded, and a spar of cartilage,
nah; “keel”), projects posteriorly from
its inner face, marking the point where the trachea branches
into the two
. Te mucosa of the carina is highly
sensitive and violent coughing is triggered when a foreign ob-
ject makes contact with it.
By the time incoming air reaches the end of the trachea, it
is warm, cleansed of most impurities, and saturated with water
²racheal obstruction is life threatening. Many people have suf-
focated a±er choking on a piece of food that suddenly closed oﬀ
their trachea. Te
, a procedure in which air
in the victim’s lungs is used to “pop out,” or expel, an obstructing
piece of food, has saved many people from becoming victims of
“café coronaries.” Te maneuver is simple to learn and easy to do.
However, it is best learned by demonstration because cracked ribs
are a distinct possibility when it is done incorrectly.
Check Your Understanding
Air moving from the nose to the trachea passes by a number
of structures. List (in order) as many of these structures as
Which structure seals the larynx when we swallow?
Which structural features of the trachea allow it to expand
and contract, yet keep it from collapsing?
For answers, see Appendix H.
The Bronchi and Subdivisions
Distinguish between conducting and respiratory zone
Describe the makeup of the respiratory membrane, and
relate structure to function.