854
UNIT 4
Maintenance of the Body
23
Check Your Understanding
6.
How does the location of the visceral peritoneum differ from
that of the parietal peritoneum?
7.
Of the following organs, which is/are retroperitoneal?
Stomach, pancreas, liver.
8.
What name is given to the venous portion of the splanchnic
circulation?
For answers, see Appendix H.
Histology of the Alimentary Canal
Describe the tissue composition and general function of
each of the four layers of the alimentary canal.
Each digestive organ has only a share of the work of digestion.
Consequently, it helps to consider structural characteristics that
promote similar functions in all parts of the alimentary canal be-
fore we consider the functional anatomy of each digestive organ.
From the esophagus to the anal canal, the walls of the alimen-
tary canal have the same four basic layers, or
tunics
mucosa,
submucosa, muscularis externa
, and
serosa
(Figure 23.6)
. Each
layer contains a predominant tissue type that plays a specific role
in food breakdown.
feces all over the peritoneum. In peritonitis, the peritoneal cov-
erings tend to stick together around the infection site. Tis lo-
calizes the infection, providing time for macrophages to prevent
the inflammation from spreading.
If peritonitis becomes widespread within the peritoneal cav-
ity, it is dangerous and o±en lethal. ²reatment includes remov-
ing as much infectious debris as possible and administering
megadoses of antibiotics.
Blood Supply: The Splanchnic Circulation
Define splanchnic circulation.
Indicate the importance of the hepatic portal system.
Te
splanchnic circulation
includes those arteries that branch
off the abdominal aorta to serve the digestive organs and the
hepatic portal circulation
. Te arterial supply—the branches
of the celiac trunk that serve the spleen, liver, and stomach,
and the mesenteric arteries that serve the small and large intes-
tines (see pp. 875 and 887)—normally receives one-quarter of
the cardiac output. Tis percentage increases a±er a meal. Te
hepatic portal circulation (pp. 742–743) collects nutrient-rich
venous blood draining from the digestive viscera and delivers
it to the liver.
Glands in submucosa
Submucosa
Lumen
Mucosa-associated
lymphoid tissue
Duct of gland outside
alimentary canal
Gland in mucosa
Nerve
Artery
Vein
Lymphatic vessel
Mesentery
Intrinsic nerve plexuses
Myenteric nerve plexus
Submucosal nerve plexus
Mucosa
Epithelium
Lamina propria
Muscularis mucosae
Muscularis externa
Longitudinal muscle
Circular muscle
Serosa
Epithelium (mesothelium)
Connective tissue
Figure 23.6
Basic structure of the alimentary canal.
Its four basic layers are the mucosa,
submucosa, muscularis externa, and serosa.
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