Page 146 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Esophagus
The musculature in the upper third of the a scissor-like manner, so that the sphincter
esophageal wall is partly made up of striated is automatically clamped when the dia-
muscle, partly of smooth muscle. On swal- phragm contracts. An intact phrenico-esoph-
lowing (deglutition) the upper esophageal ageal ligament (→ E1) and a relatively acute
sphincter opens reflexly and a (primary) peri- angle of His between the end of the esopha-
staltic reflex wave moves the bolus of food gus and the stomach are also important in
into the esophagus. Here the dilation by the providing reflux protection during swallow-
bolus initiates further (secondary) peristaltic ing.
waves that continue until the bolus has Factors that lower sphincter pressure will
reached the stomach. The lower esophageal promote reflux. Among these are vasoactive
Liver sphincter is opened by a vagovagal reflex at intestinal polypeptide (VIP) and ATP, the
the beginning of the swallowing action. This
transmitters of the inhibitory NCNA neurones
Stomach, Intestines, inhibitory noncholinergic nonadrenergic nists, hormones such as secretin, cholecysto-
as well as dopamine and β-adrenergic ago-
receptive relaxation reflex is mediated by the
kinine (CCK), progesterone, and glucose–de-
(NCNA) neurones of the myenteric plexus
pendent insulinotropic peptide (GIP = for-
(→ A).
merly: gastric inhibitory polypeptide), para-
Esophageal motility, for example, the pro-
crine substances (NO, PGI 2 , PGE 2 ), a progester-
gression of the peristaltic wave, is usually
ious segments of the esophagus (→ A1,2).
fat content, and many others.
Sporadic reflux of gastric juice is an every-
The resting pressure within the lower esoph-
6 tested by pressure measurements in the var- one effect during pregnancy, food with a high
ageal sphincter is ca. 20–25 mmHg. During day physiological event, either from unex-
receptive relaxation the pressure falls to the pected pressure on a full stomach, or during
few mmHg that prevail in the proximal swallowing (opening of sphincter for a few
stomach (→ A3), indicating opening of the seconds; → B5, right), or during transient
sphincter. openings of the sphincter (→ B5, left) that
The lower esophageal sphincter is usually last up to half a minute and are triggered by
closed, just like its upper counterpart. This marked dilation of the stomach wall and not
barrier against reflux of the harmful gastric by the act of swallowing. These transient
juice (pepsin and HCl) is strengthened when sphincter openings are probably part of the
the sphincter pressure is raised (→ B), for ex- expulsion reflex through which swallowed
ample, by the action of acetylcholine liber- air and CO 2 can be expelled from the stom-
ated from the ganglion cells of the myenteric ach. The fact that significant reflux occurs as
plexus, or by adrenergic agonists, by hor- a consequence can be concluded from the
mones, such as gastrin (reflux protection dur- marked drop in pH in the distal esophagus
ing digestive gastric motility), motilin (reflux (→ B4).
protection during interdigestive motility), Three mechanisms are responsible for
somatostatin, and substance P, by paracrine protecting the esophageal mucosa after re-
action (histamine, PGF 2α ), by protein-rich flux:
food, or by high intra-abdominal pressure ! Volume clearance, i.e., the rapid replace-
(contraction of abdominal muscles, obesity, ment of reflux volume into the stomach by
ascites). This pressure would tear open the the esophageal peristalsis reflex. Reflux vol-
sphincter but for the fact that part of the 3– ume of 15 mL, except for a small residual
4 cm long lower esophageal sphincter lies amount, normally remains in the esophagus
within the abdominal space. As a conse- for only five to 10 seconds (→ B1).
quence, the sphincter pressure is increased ! pH clearance. Residual gastric juice, left
(from outside) in proportion to the increase behind by the volume clearance, has an un-
in intra-abdominal pressure. Furthermore, changed, low pH. It only rises, step by step
136 parts of the diaphragm surround the lower (→ B2), with each act of swallowing (→ B3),
esophageal sphincter (left and right crux) in i.e., the swallowed saliva buffers the residual
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Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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