210
UNIT 3
Organ Systems
Figure 11-8A.
Bronchus, secondary bronchus.
H&E,
3
11
The trachea bifurcates to give rise to two main bronchi
(
primary bronchi
), which are also called
extrapulmonary
bronchi
because they have not yet entered the lungs. Primary
bronchi give rise to
secondary bronchi
and continue to divide
into
tertiary bronchi
. The extrapulmonary bronchi have a
similar structure to the trachea; the cartilage is still C-shaped
and lined with ciliated pseudostratiF
ed columnar epithelium.
Bronchi that enter the lung tissue are called
intrapulmonary
bronchi
; they include the
secondary bronchi
and
tertiary
(
seg-
mental
)
bronchi
. Here is an example of a secondary bronchus,
which has bifurcated from a primary bronchus at the hilus just
above the entry to the lung. Large plates of
hyaline cartilage
,
no longer C-shaped, provide support for the secondary bron-
chi. Bronchi are also covered by respiratory epithelium.
Hyaline cartilage
plates
Fig. 11-8B
Lumen of bronchus
Lumen of
bronchus
A
Respiratory epithelium
Respiratory
epithelium
Respiratory
epithelium
Smooth muscle
Goblet cells
Mucosa
Mucosa
Mucosa
Submucosa
Duct of
the glands
Hyaline
Hyaline
cartilage
cartilage
Hyaline
cartilage
Smooth
muscle
Bronchial
glands
Lamina propria
B
Figure 11-8B.
Bronchus, secondary bronchus.
H&E,
3
37;
inset
3
198
Secondary bronchi
are also called
lobar bronchi
. The right
lung has three lobar bronchi, and the left lung has two lobar
bronchi. The epithelial lining of secondary bronchi is similar
to that of the trachea and primary bronchi.
Goblet cells
can
be seen in this F
gure interspersed in the ciliated pseudostrati-
F
ed columnar epithelium. There is a band of
smooth muscle
that is arranged in a spiral fashion between the
mucosa
and
submucosa
that surround the lumen of the bronchi. This
smooth muscle is controlled by the
sympathetic
and
parasym-
pathetic nervous systems
.
Sympathetic f
bers
cause
relaxation
of the smooth muscle;
parasympathetic f
bers
cause smooth
muscle to
contract
, reducing the diameter of the lumen of the
bronchi.
Bronchial glands
(
seromucous glands
) located in the
submucosa, and the
ducts
of these glands, are visible in this
specimen.
Figure 11-8C.
Bronchus, tertiary bronchus.
H&E,
3
17
Secondary bronchi
divide into
tertiary bronchi
, also known
as
segmental bronchi
. These decrease in size as they branch
distally within the lung. Two tertiary bronchi are shown here.
The luminal surfaces of the tertiary bronchi are covered with
respiratory epithelium;
smooth muscle
and submucosal glands
are also present.
Elastic f
bers
are prominent in the lamina pro-
pria and are stained red in this example. The
cartilage plates
of the tertiary bronchi are smaller than the plates in the sec-
ondary bronchi. As the tertiary bronchi continues to branch,
their diameters gradually decrease; as the cartilage plates
become smaller and fewer, the bronchial glands and goblet
cells decrease in number as well.
The right primary bronchus is wider and shorter and more
vertical than the left one;
±oreign body aspiration
happens
more often to the right lung than to the left lung.
Mixed
Mixed
glands
glands
Mixed
Mixed
glands
glands
Cartilage
Cartilage
plates
plates
Cartilage
Cartilage
plates
plates
Cartilage
plates
Cartilage
Cartilage
plates
plates
Cartilage
plates
Lumen of a
Lumen of a
small bronchus
small bronchus
Lumen of a
small bronchus
Smooth
Smooth
muscle
muscle
Smooth
muscle
Bronchioles
Bronchioles
Bronchioles
Blood vessels
Blood vessels
Blood vessels
Mixed
Mixed
glands
glands
Mixed
glands
Lumen of a
Lumen of a
bronchus
bronchus
Lumen of a
bronchus
Elastic fibers
Elastic fibers
Elastic fibers
C
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