CHAPTER 6
Muscle
111
CLINICAL CORRELATION
Figure 6-11C.
Chronic Asthma.
H&E,
3
27
Asthma
is a chronic condition characterized by
wheezing, shortness of breath, chest tightness, and
coughing. Respiratory airways are hypersensitive and
hyperresponsive to a variety of stimuli. Clinical F nd-
ings include airfl ow obstruction caused by smooth
muscle constriction around airways, airway mucosal
edema, intraluminal mucus accumulation, infl amma-
tory cell inF ltration in the submucosa, and basement
membrane thickening. During acute asthma attacks,
spasms of smooth muscle together with excessive
mucous secretion may close off airways and may be
fatal. Pathologic F ndings include
smooth muscle thick-
ening
(
hypertrophy
and
hyperplasia
), and remodeling
of nearby small and mid-sized pulmonary blood ves-
sels. Treatment includes using combinations of drugs
and environmental and lifestyle changes.
Thickening (hypertrophy
and hyperplasia)
of smooth muscle layer
Airway plugged by
cell debris
and
mucus
C
Figure 6-11A.
Smooth muscle in the wall of the uterus.
H&E,
3
136
In most locations, fascicles of smooth muscle are oriented in
the same direction. However, in hollow organs in which the
overall size of the organ is reduced by smooth muscle con-
traction, such as the
uterus
, the fascicles are intertwined and
run in all different directions. In this section, some fascicles
are cut in a longitudinal plane, some in a tangential plane,
and others are cut diagonally.
A
Smooth muscle
Smooth muscle
Bronchiole
Smooth muscle
Ciliated columnar/
Ciliated columnar/
cuboidal epithelium
cuboidal epithelium
Ciliated columnar/
cuboidal epithelium
B
Figure 6-11B.
Smooth muscle in a bronchiole.
H&E,
3
136; inset
3
160
Smooth muscle
lines the walls of the bronchioles in the respi-
ratory system (see ±igs 11-9 to 11-11). It relaxes to increase
the size of the airway passages under the infl uence of the
sympathetic nervous system and hormones controlled by
the sympathetic nervous system, and it contracts to reduce
the size of the airway passages under the infl uence of the
parasympathetic nervous system. This smooth muscle aids
in expelling air from the lungs during breathing. It is also
important in the cough refl ex, which helps to expel foreign
matter such as dust, smoke, and excess mucus from the lungs.
With age, and in response to irritants such as tobacco smoke,
the contractility of smooth muscle may be reduced, causing
respiratory insufF ciency. Note the long, thin,
spindle-shaped
nuclei of the smooth muscle cells in the
inset
.
The large forces generated by uterine smooth muscle are
important in
expelling the fetus during childbirth
and are also
critical for
clamping down on blood vessels
to stop bleeding
after the placenta is pulled away from its attachment to the
wall of the uterus. Contraction of this smooth muscle can
be enhanced by the administration of
oxytocic agents
(e.g.,
oxytocin
,
ergonovine
) after delivery to stimulate myometrial
contractions and prevent or treat
postpartum hemorrhage
.
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