Chapter 23
The Digestive System
853
23
and duodenum (the first part of the small intestine), and parts
of the large intestine, are called
retroperitoneal organs
(
retro
5
behind). By contrast, digestive organs (like the stomach) that
keep their mesentery and remain in the peritoneal cavity are
called
intraperitoneal
or
peritoneal organs
.
Homeostatic Imbalance
23.1
Peritonitis
is inflammation of the peritoneum. It can arise from
a piercing abdominal wound, a perforating ulcer that leaks
stomach juices into the peritoneal cavity, or poor sterile tech-
nique during abdominal surgery. However, most commonly it
results from a burst appendix that sprays bacteria-containing
the digestive viscera; hold organs in place; and store fat. In most
places the mesentery is
dorsal
and attaches to the posterior ab-
dominal wall, but there are
ventral
mesenteries too, such as the
one that extends from the liver to the anterior abdominal wall
(Figure 23.5a). Some digestive organ mesenteries have specific
names (such as the
omenta
), or are called “ligaments” (even
though these peritoneal folds are nothing like the fibrous liga-
ments that connect bones).
Not all alimentary canal organs are suspended by a mesentery.
For example, during development, some regions of the small in-
testine adhere to the dorsal abdominal wall (Figure 23.5b). In so
doing, they lose their mesentery and come to lie posterior to the
peritoneum. Tese organs, which include most of the pancreas
External stimuli
(sight, smell, taste,
thought of food)
Central nervous system
Visceral afferents
Extrinsic visceral (autonomic)
efferents
Long reflexes
Internal
(GI tract)
stimuli
Chemoreceptors,
osmoreceptors, or
mechanoreceptors
Local (intrinsic)
nerve plexus
(“gut brain”)
Effectors:
Smooth muscle
or glands
Gastrointestinal
wall (site of short
reflexes)
Response:
Change in
contractile or
secretory activity
Lumen of the
alimentary canal
Short reflexes
Figure 23.4
Neural reflex pathways initiated by stimuli inside or outside the
gastrointestinal tract.
Peritoneal
cavity
Parietal
peritoneum
Visceral
peritoneum
Ventral
mesentery
Abdominopelvic
cavity
Mesentery
resorbed
and lost
Dorsal
mesentery
Vertebra
Alimentary
canal organ
(a) Two schematic cross sections of abdominal cavity illustrate
the peritoneums and mesenteries.
(b) Some organs lose their mesentery and move,
becoming retroperitoneal, during development.
Alimentary
canal organ
Alimentary canal organ in
a retroperitoneal position
Liver
Figure 23.5
The peritoneum and the peritoneal cavity.
Note that the peritoneal cavity is
much smaller than depicted here.
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