208
UNIT 3
Organ Systems
Conducting Portion: Lower Respiratory Airway
Figure 11-6A.
Trachea.
H&E,
3
7
The
trachea
is a fl
exible tube that connects the larynx to the
primary bronchi. It is about 10 to 12 cm long, 2 to 2.5 cm in
diameter, and is located immediately anterior to the esopha-
gus. It is composed of
mucosa
,
submucosa
,
hyaline
cartilage
,
and
adventitia
. (1) The
mucosa
covers the inner surface of
the trachea and contains respiratory epithelium and the lam-
ina propria. (2) The
submucosa
contains connective tissue,
which is denser than the lamina propria. (3)
Hyaline cartilage
has a unique C-shape (some animals, e.g., the rat, may have
O-shaped cartilage), and there are about 16 to 20 rings in the
trachea. (4) The
adventitia
is composed of connective tissue,
which covers the outer surface of the cartilage and connects
the trachea to the adjacent structures. There are some elastic
connective tissues and smooth muscles (
trachealis muscle
) in
the opening between the two ends of the cartilage; this stabi-
lizes the opening.
Cartilage ring
Mucosa
Submucosa
Adventitia
Trachealis muscle
A
L
a
m
in
in
a
p
p
ro
r
o
p
ria
r
ia
S
u
b
m
u
c
o
s
a
Adventitia
Adventitia
Respiratory
epithelium
Respiratory
epithelium
Perichondrium
Tracheal cartilage
(hyaline cartilage)
Glands in
submucosa
Submucosa
Lamina propria
L
a
m
in
in
a
p
ro
r
o
p
ria
r
ia
Lamina
propria
Adventitia
B
Figure 11-6B.
Trachea.
H&E,
3
35; inset
3
146
The luminal surface of the
trachea
is covered by
ciliated pseu-
dostratif
ed columnar epithelium
, also called
respiratory epi-
thelium
(Fig 11-7A,B). The epithelium plus the
lamina propria
constitute the
mucosa
. The lamina propria is a layer of loose
connective tissue beneath the epithelium. The
submucosa
is
a layer of dense connective tissue located between the lam-
ina propria and cartilage; it contains many
trachealis glands
(
seromucous glands
). Mucin and watery secretions from tra-
cheal glands are delivered through their ducts to the surface
of the epithelium (Fig. 11-6C). The C-shaped hyaline cartilage
rings (
tracheal cartilages
) provide support for the trachea.
They are covered by
perichondrium
and many chondrocytes
are embedded in their matrix (see Fig. 5-2B).
Trachealis muscle
Trachealis muscle
(smooth muscle)
(smooth muscle)
Trachealis
Trachealis
glands
glands
Duct of
Duct of
glands
glands
Trachealis muscle
Trachealis muscle
(smooth muscle)
(smooth muscle)
Tracheal cartilage
(hyaline cartilage)
Trachealis muscle
(smooth muscle)
Trachealis
glands
Duct of
glands
Trachealis muscle
(smooth muscle)
C
Figure 11-6C.
Trachealis muscle, trachea.
H&E,
3
35;
inset
3
100
The
trachealis muscle
is a smooth muscle located between the
open ends of the C-shaped cartilage rings. Trachealis muscle
± bers attach directly to the perichondrium of the cartilage
together with connective tissue, which stabilizes the cartilage’s
open ends. The contraction and expansion of smooth muscle
help to adjust the airfl ow through the trachea.
If a foreign object enters the airway, smooth muscle in the
trachea and bronchi contracts, narrowing the lumina, help-
ing to induce coughing. (
Cough refl ex
: cooperation among
the epiglottis, vocal cords, trachea, bronchi, lungs, respira-
tory muscles, and the autonomic nervous system). In
asthma
,
the smaller airways (bronchi and bronchioles) are narrowed
because of excessive contraction of the smooth muscle of the
lower airway in response to histamine released in an allergic
reaction (see Fig. 6-11C).
previous page 223 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online next page 225 Dongmei Cui -  Atlas of Histology with Functional and Clinical Correlations 2011 read online Home Toggle text on/off