806
UNIT 4
Maintenance of the Body
22
The Nasopharynx
Te
nasopharynx
is posterior to the nasal cavity, inferior to the
sphenoid bone, and superior to the level of the soF palate. Because
it lies above the point where food enters the body, it serves
only
as
an air passageway. During swallowing, the soF palate and its pen-
dulous
uvula
(u
9
vu-lah; “little grape”) move superiorly, an action
that closes off the nasopharynx and prevents food from entering
the nasal cavity. (When we giggle, this sealing action fails and flu-
ids being swallowed can end up spraying out the nose.)
Te nasopharynx is continuous with the nasal cavity through
the posterior nasal apertures (±igure 22.3b). Its pseudostratified
ciliated epithelium takes over the job of propelling mucus where
the nasal mucosa leaves off. High on its posterior wall is the
pharyngeal
tonsil
(far-rin
9
je-al) (or
adenoids
), which traps and
destroys pathogens entering the nasopharynx in air.
Homeostatic Imbalance
22.2
Infected and swollen adenoids block air passage in the na-
sopharynx, making it necessary to breathe through the mouth.
As a result, the air is not properly moistened, warmed, or fil-
tered before reaching the lungs. When the adenoids are chroni-
cally enlarged, both speech and sleep may be disturbed.
Te
pharyngotympanic
(
auditory
)
tubes
, which drain the
middle ear cavities and allow middle ear pressure to equalize
with atmospheric pressure, open into the lateral walls of the
nasopharynx (±igure 22.3a). A ridge of pharyngeal mucosa pos-
terior to each of these openings constitutes the
tubal tonsil
. Its
strategic location helps protect the middle ear against infections
likely to spread from the nasopharynx.
The Oropharynx
Te
oropharynx
lies posterior to the oral cavity and is continu-
ous with it through an archway called the
isthmus of the fauces
(faw
9
sēz; “throat”) (±igure 22.3b). Because the oropharynx ex-
tends inferiorly from the level of the soF palate to the epiglottis,
both swallowed food and inhaled air pass through it.
As the nasopharynx blends into the oropharynx, the epithe-
lium changes from pseudostratified columnar to a more protective
stratified squamous epithelium. Tis structural adaptation accom-
modates the increased friction and chemical trauma (characteristic
of hot and spicy foods) accompanying food passage.
Te paired
palatine tonsils
lie embedded in the lateral walls
of the oropharyngeal mucosa just posterior to the oral cavity.
Te
lingual tonsil
covers the posterior surface of the tongue.
The Laryngopharynx
Like the oropharynx above it, the
laryngopharynx
(lah-ring
0
go-
far
9
ingks) serves as a passageway for food and air and is lined
with a stratified squamous epithelium. It lies directly posterior
to the upright epiglottis and extends to the larynx, where the
respiratory and digestive pathways diverge. At that point the
laryngopharynx is continuous with the esophagus posteriorly.
Te esophagus conducts food and fluids to the stomach; air
enters the larynx anteriorly. During swallowing, food has the
“right of way,” and air passage temporarily stops.
(±igure 22.3). Te groove inferior to each concha is a
nasal mea-
tus
(me-a
9
tus).
Te curved conchae greatly increase the mucosal surface
area exposed to air and enhance air turbulence in the cavity.
Te gases in inhaled air swirl through the twists and turns, de-
flecting heavier, nongaseous particles onto the mucus-coated
surfaces, where they become trapped. As a result, few particles
larger than 6 μm make it past the nasal cavity.
Te conchae and nasal mucosa not only function dur-
ing inhalation to filter, heat, and moisten the air, but also act
during exhalation to reclaim this heat and moisture. In other
words, inspired air cools the conchae, then during exhalation
these cooled conchae precipitate moisture and extract heat
from the humid air flowing over them. Tis reclamation pro-
cess minimizes the amount of moisture and heat lost from the
body through breathing, helping us to survive in dry and cold
climates.
Paranasal Sinuses
Te nasal cavity is surrounded by a ring of
paranasal
sinuses
(±igure 22.3b). Tey are located in the frontal, sphenoid, eth-
moid, and maxillary bones (see ±igure 7.14, p. 215). Te sinuses
lighten the skull, and together with the nasal cavity they warm
and moisten the air. Te mucus they produce ultimately flows
into the nasal cavity, and the suctioning effect created by nose
blowing helps drain the sinuses.
Homeostatic Imbalance
22.1
Cold viruses, streptococcal bacteria, and various allergens can
cause
rhinitis
(ri-ni
9
tis), inflammation of the nasal mucosa ac-
companied by excessive mucus production, nasal congestion,
and postnasal drip. Te nasal mucosa is continuous with the
mucosa of the respiratory tract, explaining the typical nose to
throat to chest progression of colds. Because the mucosa extends
tentacle-like into the nasolacrimal (tear) ducts and paranasal
sinuses, nasal cavity infections oFen spread to those regions,
causing
sinusitis
(inflamed sinuses).
When mucus or infectious materials block the passageways
connecting the sinuses to the nasal cavity, the air in the sinus
cavities is absorbed. Te result is a partial vacuum and a
sinus
headache
localized over the inflamed areas.
The Pharynx
Te funnel-shaped
pharynx
(far
9
ingks) connects the nasal cav-
ity and mouth superiorly to the larynx and esophagus inferiorly.
Commonly called the
throat
, the pharynx vaguely resembles
a short length of garden hose as it extends for about 13 cm
(5 inches) from the base of the skull to the level of the sixth cer-
vical vertebra (±igure 22.1).
±rom superior to inferior, the pharynx is divided into three
regions—the
nasopharynx, oropharynx
, and
laryngopharynx
(±igure 22.3c). Te muscular pharynx wall is composed of skel-
etal muscle throughout its length (see ²able 10.3, pp. 334–335).
However, the cellular composition of its mucosa varies from
one pharyngeal region to another.
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