Page 876 - Fundamentals of anatomy physiology

The Pharynx
The pharynx (FAR-ingks), or throat, is a chamber shared by the
digestive and respiratory systems. It extends between the internal
nares and the entrances to the larynx and esophagus. The curving
superior and posterior walls of the pharynx are closely bound to
the axial skeleton, but the lateral walls are flexible and muscular.
We can divide the pharynx into the nasopharynx, the
o­ ropharynx, and the laryngopharynx (Figure 23–3c):
1. The nasopharynx is the superior portion of the pharynx.
It is connected to the posterior portion of the nasal cavity
through the internal nares. The soft palate separates it from
the oral cavity. The nasopharynx is lined by the same pseu-
dostratified ciliated columnar epithelium as in the nasal
cavity. The pharyngeal tonsil is located on the posterior wall
of the nasopharynx. Each auditory tube opens into the na-
sopharynx at the nasopharyngeal meatus on either side of
this tonsil. pp. 617, 816
2. The oropharynx (oris, mouth) extends between the soft
palate and the base of the tongue at the level of the hyoid
bone. The posterior portion of the oral cavity communi-
cates directly with the oropharynx, as does the posterior
inferior portion of the nasopharynx. At the boundary be-
tween the nasopharynx and the oropharynx, the epithe-
lium changes from pseudostratified columnar epithelium
to stratified squamous epithelium.
3. The narrow laryngopharynx (la-rin-go. -FAR-ingks) is the in-
ferior part of the pharynx. It includes that portion of the phar-
ynx between the hyoid bone and the entrance to the larynx
and esophagus. Like the oropharynx, the laryngopharynx is
lined with a stratified squamous epithelium that resists abra-
sion, chemical attack, and invasion by pathogens.
Checkpoint
4. Name the structures of the upper respiratory system.
5. Why is the vascularization of the nasal cavity important?
6. Why is the lining of the nasopharynx different from
that of the oropharynx and the laryngopharynx?
See the blue Answers tab at the back of the book.
23-3 Composed of cartilages,
ligaments, and muscles, the larynx
produces sound
Learning Outcome Describe the structure of the larynx, and discuss its arytenoid cartilage and the epiglottis (Figures 23–4c and 23–5).
roles in normal breathing and in sound production.
Inhaled air leaves the pharynx and enters the larynx through
a narrow opening of the glottis. The glottis is the vocal appa-
ratus, or “voice box,” of the larynx. The larynx (LAR-ingks)
is a cartilaginous tube that surrounds and protects the glottis.
Chapter 23 The Respiratory System 863
The l­arynx begins at the level of vertebra C4 or C5 and ends at
the level of vertebra C6. Essentially a cylinder, the larynx has
incomplete cartilaginous walls that are stabilized by ligaments
and skeletal muscles (Figure 23–4).
Cartilages and Ligaments of the Larynx
Three large, unpaired cartilages form the larynx: (1) the thy-
roid cartilage, (2) the cricoid cartilage, and (3) the epiglottis
(Figure 23–4). The thyroid cartilage (thyroid, shield shaped)
is the largest laryngeal cartilage. Made of hyaline cartilage, it
forms most of the anterior and lateral walls of the larynx. In
section, this cartilage is U-shaped, and posteriorly, it is incom-
plete. You can easily see and feel the prominent anterior surface
of the thyroid cartilage, called the laryngeal prominence or Adam’s
apple. The inferior surface articulates with the cricoid cartilage.
The superior surface has ligamentous attachments to the hyoid
bone and to the epiglottis and smaller laryngeal cartilages.
The thyroid cartilage sits superior to the cricoid (KRI.-
koyd; ring shaped) cartilage, another hyaline cartilage. The
posterior portion of the cricoid is greatly expanded, providing
support in the absence of the thyroid cartilage. The cricoid and
thyroid cartilages protect the glottis and the entrance to the
trachea. Their broad surfaces provide sites for the attachment of
important laryngeal muscles and ligaments. Ligaments attach
the inferior surface of the cricoid cartilage to the first tracheal
cartilage. The superior surface of the cricoid cartilage articulates
with the small, paired arytenoid cartilages.
The shoehorn-shaped epiglottis (ep-i-GLOT-is) projects
superior to the glottis and forms a lid over it. The epiglottis is
composed of elastic cartilage. It has ligamentous attachments
to the anterior and superior borders of the thyroid cartilage
and the hyoid bone. During swallowing, the larynx is elevated
and the epiglottis folds back over the glottis, preventing both
liquids and solid food from entering the respiratory tract.
The larynx also contains three pairs of smaller hyaline
23cartilages: (1) The arytenoid (ar-i-TE. -noyd; ladle shaped)
cartilages articulate with the superior border of the enlarged
portion of the cricoid cartilage. (2) The corniculate (kor-NIK-
u. -la. t; horn shaped) cartilages articulate with the arytenoid
cartilages. The corniculate and arytenoid cartilages function
in the opening and closing of the glottis and the production
of sound. (3) Elongated, curving cuneiform (ku. -NE. -i-form;
wedge shaped) cartilages lie within folds of tissue (the ary-
epiglottic folds) that extend between the lateral surface of each
Ligaments bind together the various laryngeal cartilages.
Additional ligaments attach the thyroid cartilage to the hyoid
bone, and the cricoid cartilage to the trachea (cricotracheal liga-
ment) (Figure 23–4a,b). The median cricothyroid ligament at-
taches the thyroid cartilage to the cricoid cartilage. Because it has
easily identifiable landmarks and is clear of the thyroid gland,