Ganong's Review of Medical Physiology, 23rd Edition

CHAPTER 28

Gastrointestinal Motility 471

(which suppresses motilin release via mechanisms that have not
yet been elucidated), with a return to peristalsis and the other
forms of BER and spike potentials.

SEGMENT-SPECIFIC PATTERNS

OF MOTILITY

MOUTH & ESOPHAGUS

In the mouth, food is mixed with saliva and propelled into the
esophagus. Peristaltic waves in the esophagus move the food
into the stomach.

MASTICATION

Chewing
(mastication)
breaks up large food particles and
mixes the food with the secretions of the salivary glands. This
wetting and homogenizing action aids swallowing and subse-
quent digestion. Large food particles can be digested, but they
cause strong and often painful contractions of the esophageal
musculature. Particles that are small tend to disperse in the ab-
sence of saliva and also make swallowing difficult because they
do not form a bolus. The number of chews that is optimal de-
pends on the food, but usually ranges from 20 to 25.
Edentulous patients are generally restricted to a soft diet
and have considerable difficulty eating dry food.

SWALLOWING

Swallowing (deglutition) is a reflex response that is triggered

by afferent impulses in the trigeminal, glossopharyngeal, and

vagus nerves (Figure 28–3). These impulses are integrated in

the nucleus of the tractus solitarius and the nucleus ambiguus.

The efferent fibers pass to the pharyngeal musculature and the

tongue via the trigeminal, facial, and hypoglossal nerves. Swal-

lowing is initiated by the voluntary action of collecting the oral

contents on the tongue and propelling them backward into the

pharynx. This starts a wave of involuntary contraction in the

pharyngeal muscles that pushes the material into the esopha-

gus. Inhibition of respiration and glottic closure are part of the

reflex response. A peristaltic ring contraction of the esoph-

ageal muscle forms behind the material, which is then swept

down the esophagus at a speed of approximately 4 cm/s. When

humans are in an upright position, liquids and semisolid foods

generally fall by gravity to the lower esophagus ahead of the

peristaltic wave.

LOWER ESOPHAGEAL SPHINCTER

Unlike the rest of the esophagus, the musculature of the gas-

troesophageal junction

(lower esophageal sphincter; LES)

is

tonically active but relaxes on swallowing. The tonic activity of

the LES between meals prevents reflux of gastric contents into

the esophagus. The LES is made up of three components (Fig-

ure 28–4). The esophageal smooth muscle is more prominent

FIGURE 28–2
Basic electrical rhythm (BER) of gastrointestinal smooth muscle. Top:
Morphology, and relation to muscle contraction.
Bottom:
Stimulatory effect of acetylcholine and inhibitory effect of epinephrine.
(Modified and reproduced with permission from Chang EB, Sitrin MD, Black
DD:
Gastrointestinal, Hepatobiliary, and Nutritional Physiology.
Lippincott-Raven, 1996.)

Electrical

recording

Mechanical

recording

(tension)

Electrical

recording

Mechanical

recording

< 15

< 50

<50 mV

<15 mV

1.5 g

1.5 g

mV

Spike potentials

10 s

10 s

Acetylcholine Epinephrine

BER