200
UNIT 3
Organ Systems
Figure 11-13A,B
Type I Pneumocytes
Figure 11-14A,B
Type II Pneumocytes
Figure 11-15A,B
Alveolar Macrophages
Figure 11-16A
Clinical Correlation: Acute Respiratory Distress Syndrome
Figure 11-16B
Clinical Correlation: Emphysema
Synopsis 11-1
Pathological and Clinical Terms for the Respiratory System
Table 11-1
Respiratory System
Synopsis 11-2
Structural Differences (from Upper to Lower Airway) in the Respiratory System
Introduction and Key Concepts
for the Respiratory System
The primary function of the
respiratory system
is to supply the
body’s need for oxygen and to give off carbon dioxide. Other
functions include maintaining homeostasis and a normal pH
and participating in the body’s immune defense against bacte-
rial and viral infections. Anatomically, the respiratory system
can be divided into an
upper respiratory airway
and a
lower
respiratory airway
. Functionally, the respiratory system can
be divided into a
conducting portion
for the transportation
of gases and a
respiratory portion
for gas exchange. The
con-
ducting portion
includes the
upper respiratory airway
and the
lower respiratory airway
. These conducting airways include
the
nasal cavity
,
pharynx
,
larynx
,
trachea
,
extrapulmonary
and
intrapulmonary bronchi
,
bronchioles
, and
terminal bronchi-
oles
. The
respiratory portion
includes the
respiratory bronchi-
oles
,
alveolar ducts
,
alveolar sacs
, and
alveoli
. The respiratory
muscles (skeletal muscles: external intercostal muscle and the
diaphragm) play an important role in producing the movement
of air into and out of the lungs. The sympathetic and para-
sympathetic nervous systems innervate the smooth muscle of
the bronchial tree as well as the mucous membranes and blood
vessels in the lungs. Sympathetic ± bers cause
bronchodilation
(relaxation of bronchial smooth muscles), whereas parasym-
pathetic ± bers cause
bronchoconstriction
(contraction of bron-
chial smooth muscles).
Conducting Portion
Upper Respiratory Airway
The
upper respiratory airway
functions as a part of the
con-
ducting portion
; it consists of the
nasal cavity
,
nasopharynx,
oropharynx
, and
larynx
. In general, the conducting airway is
composed of bone, cartilage, and ±
brous tissue and is lined
with strati±
ed squamous and ciliated pseudostrati±
ed columnar
epithelia moistened with mucus and other glandular secretions.
Cilia on the surface of the pseudostrati±
ed columnar epithelia
sweep particles out of the respiratory airway.
THE NASAL CAVITY
is the ± rst portion of the upper respira-
tory airway. It can be divided into three regions based on the
types of epithelial coverings. (1) The
nasal vestibule
is the most
anterior part of the nasal cavity and is covered by a keratinized
strati±
ed squamous epithelium and
vibrissae
(stiff hairs); it is
continuous with a mucosa of nonkeratinized strati± ed squamous
epithelium (Fig. 11-3A). (2) The
nasal mucosa region
is covered
by pseudostrati±
ed ciliated epithelium (respiratory epithelium),
which contains ciliated columnar cells, goblet cells, basal cells,
and, occasionally, neuroendocrine cells (Figs. 11-3B and 11-7).
The goblet cells manufacture
mucus
, which traps particles
of dust and bacteria and moves them out of the nasal fossa,
sinuses, and the nasopharynx, with the help of the ciliary action
of the epithelium. Nasal mucosa ±
lters, warms, and moistens
the inhaled air. Mucus serves as a protective mechanism for pre-
venting pathogens and irritants from entering the respiratory
airway (Fig. 11-3B,C). There is a special vascular arrangement
in the lamina propria of the nasal conchae called
swell bodies
(
venous plexuses
), which alternately ±
ll with blood from the
small arteries directly into the venous plexuses on each side of
the nasal cavity to help reduce air fl
ow and increase air contact
with nasal mucosa. (3) The
olfactory mucosa region
is located
in the roof of the nasal cavity and is covered by pseudostrati±
ed
columnar epithelium, which is composed of ciliated olfactory
cells (olfactory receptor neurons), nonciliated columnar cells,
and basal cells. It functions as a site for odorant chemorecep-
tion (Fig. 11-4A,B).
THE NASOPHARYNX AND OROPHARYNX
conduct
air from the nasal cavity and oral cavity to the larynx. The
oropharynx
is lined by strati±
ed squamous epithelium, and the
nasopharynx
is lined by respiratory (pseudostrati±
ed columnar)
epithelium (see Table 11-1). The nasopharynx contains sero-
mucous glands in the lamina propria. The
pharyngeal tonsil
, an
unencapsulated patch of lymphoid tissue, is located in the pos-
terior aspect of the nasopharynx (see Fig. 10-8A). The
palatine
tonsils
are located at the junction of the oral cavity and the oral
pharynx, between the palatoglossal and the palatopharyngeal
folds, which indicate the posterior boundary of the oral cavity
(see Fig. 10-8B). Tonsils, rich in lymphoid tissue, are the ±
rst
line of defense against many airborne pathogens and irritants.
Streptococcal pharyngitis is the most frequent bacterial upper
respiratory infection in children.
THE LARYNX
conducts air from the pharynx to the trachea.
It is supported by a set of cartilages of complex shape and cov-
ered by a ciliated, pseudostrati± ed respiratory epithelium. This
mucosa continues from that of the pharynx and extends to the
trachea. The larynx contains several structures, including the
epiglottis
,
vocal cords
, and nine pieces of cartilage located in its
wall. The
epiglottis
is a thin leafl ike plate structure; its central
cord contains a large piece of
elastic cartilage
. This cartilage is
attached to the root of the tongue and projects obliquely upward
behind the tongue and the hyoid body. The epiglottis stands in
front of the laryngeal inlet and bends posteriorly to cover the
inlet of the larynx when food is swallowed. The upper anterior
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