CHAPTER 11
Respiratory System
207
Figure 11-5A.
Epiglottis, larynx.
H&E,
3
18; inset
3
99
The
larynx
is the short passage that connects the pharynx with
the trachea; its main function is to produce sound and prevent
food or liquid from entering the trachea. Laryngeal structures
include the
epiglottis
,
vocal cords
, and nine pieces of
cartilage
located in its wall (including the thyroid cartilage—“Adam’s
apple”). The
epiglottis
is a fl attened, leaf-shaped structure with
elastic cartilage support. Classically, the epiglottis is covered by
two types of epithelia:
stratif
ed squamous
on the lingual surface
facing the oropharynx and
respiratory epithelium
on the laryn-
geal surface facing the larynx. However, this normal condition
is rarely found, because of
squamous metaplasia
(see Fig. 3-9C),
resulting from aging and irritation (even in young individuals).
The strati±
ed squamous epithelium on the lingual surface has the
distinguishing feature of
rete ridges
on its basal region, whereas
the strati±
ed squamous epithelium (squamous metaplasia) on the
laryngeal surface is fl
attened on its basal region.
CLINICAL CORRELATION
Figure 11-5C.
Age Impact on the Epiglottis.
H&E,
3
21
The integrity of the
epiglottis
is affected by age and
other factors. Structurally, variations include not only
the change from pseudostrati± ed columnar epithelium
to strati± ed squamous epithelium (
squamous meta-
plasia
[Fig. 11-5A]), but also
reduction in cartilage
size
due to replacement of the central portion of the
cartilage by a large amount of
adipose tissue
. Loss of
elastic cartilage is associated with loss of elastic ± bers
in the epiglottis. These changes result in a reduction of
the elasticity and stiffness of the epiglottis. Epiglottis
abnormalities, such as the
hypoplastic
,
bif d epiglottis
associated with
cle±t palate
in children, can cause epi-
sodic choking during food or fl uid intake. Recurrent
foreign substances entering the respiratory tract can
cause chronic infl ammation of the respiratory tract.
Nasogastric tube feeding and surgical repair of the
deformed epiglottis may be necessary in severe cases.
Reduced size
of cartilage
Remaining
cartilage
Adipose tissue
C
Rete ridge
Rete ridge
Stratified squamous
Stratified squamous
epithelium
epithelium
Stratified squamous
Stratified squamous
epithelium
epithelium
Elastic cartilage
Elastic cartilage
Lingual surface
Elastic cartilage
Laryngeal surface
Rete ridge
Stratified squamous
epithelium
Stratified squamous
epithelium
A
Elastic fibers
Elastic fibers
Elastic cartilage
Elastic cartilage
Elastic cartilage
Elastic cartilage
Mixed (mucous and serous) gland
Elastic cartilage
Elastic cartilage
Elastic fibers
B
Figure 11-5B.
Epiglottis, larynx.
Elastic ±
ber stain,
3
35; inset
3
105
This sample of
epiglottis
tissue was stained with an elastic ±
ber
stain. The
elastic f bers
are visible in
black
. Chondrocytes are
embedded with the elastic ±
bers in the cartilage matrix. Elastic
cartilage has different properties than hyaline cartilage; it forms
the framework and provides a ±
rm and elastic support for the
epiglottis. There are some
mixed glands
(most are mucous) in the
lamina propria. These glands produce mucin and a watery fl
uid
on the surface of the epiglottis. The inferior portion of the epiglot-
tis is attached to the rim of the thyroid cartilage and hyoid bone.
The superior portion is free to move up when making sounds,
and to move down to close the airway while food and fl uid are
passing through the pharynx. The main functions of the epiglot-
tis are to prevent food and fl
uid from entering the trachea and to
cooperate with the vocal cords to produce sound.
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