Deglutition • Figure 14.4
NNER
Esophagus
Relaxed
muscularis
Circular muscles
contract
a
Lower
esophageal
sphincter
y
Longitudinal muscles
contract
Relaxed muscularis
Bolus
Stomach
The process of deglutition (swallowing) involves the mouth, pharynx, and
esophagus in voluntary and involuntary phases.
Esophageal stage (involuntary):
a
Circular muscles in section above
bolus contract and push bolus
down.
b
Longitudinal muscles below bolus
contract and expand esophagus
Steps
a
and
b
repeat until bolus
reaches lower esophageal sphincter
muscle.
c
Lower esophageal sphincter relaxes
to allow bolus to enter stomach.
Afterwards it contracts to prevent
bolus from splashing back into
esophagus.
Voluntary stage:
The tongue
shapes the
chewed, lubricated
food (bolus) and
moves it to the
back of the mouth
cavity.
Bolus
Bolus
Tongue
Pharyngeal stage
(involuntary):
• The tongue rises
against the palate and
closes the
nasopharynx.
• The uvula and palate
seal off the nasal
cavity.
• The epiglottis covers
the larynx.
Breathing is temporarily
interrupted.
Swallowing Involves Voluntary
and Involuntary Stages
Once chewed, the bolus of food is swallowed, a process
called
d e g lu titio n
(de'-glu-TISH-un). Deglutition involves
several steps, including a voluntary stage, a pharyngeal
stage (involuntary), and an esophageal stage (involuntary)
(
F igu re 1 4 .4
). This process, which
involves the mouth, pharynx, and
esophagus, moves the bolus from
the mouth through the esophagus
to the stomach by waves of muscu-
lar movements called
p eristalsis
.
If the lower esophageal sphincter fails to close ad-
equately, the acidic contents of the stomach will back up
into the lower esophagus. This condition is called
g a s tr o -
e s o p h a g e a l r e flu x d is e a s e (G E R D )
. The stomach acid
irritates the mucosal lining of the esophagus and gives
the feeling of heartburn. If the condition is chronic, the
acid can permanently damage the lining of the esoph-
agus. GERD can be controlled by avoiding foods that
stimulate stomach acid secretion (such as chocolate,
coffee, tomatoes, fatty foods, and the orange juice that
goes so well with your breakfast), neutralizing the acid
with antacids, or taking drugs that inhibit stomach acid
secretion.
Once a bolus of food is inside the stomach, digestion
begins in earnest. Let’s take a closer look at the work of
this important digestive organ.
peristalsis
(per'-i-
STAL-sis) Successive
muscular contractions
along the wall of a hol-
low muscular structure.
Let's Journey Through the Digestive System 405
p r o c e ss
diagram
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