CHAPTER 15
Digestive Tract
285
Epithelium
Lamina propria
Muscularis mucosae
4. Serosa / adventitia
4. Serosa
1. Mucosa
Longitudinal
muscle
Circular
muscle
Oblique
muscle
1. Mucosa
2. Submucosa
2. Submucosa
3. Muscularis
externa
3. Muscularis
externa
Inner circular muscle
Outer longitudinal muscle
Epithelium
Lamina propria
Muscularis mucosae
2. Submucosa
1. Mucosa
3. Muscularis
externa
Circular muscle
Longitudinal muscle
band (teniae coli)
4. Serosa/adventitia
Small intestine
Stomach
Large intestine
Figure 15-3.
General structure of the wall of the digestive tract.
The
wall
of the
digestive tract
can be divided into several basic tunics (layers) based on histologic organization. (1)
Mucosa
:
epithelium,
lamina propria, and muscularis mucosae. The epithelium is composed of simple columnar cells in most of the digestive tract, except
for stratiF ed squamous cells in the esophagus and anal canal. The lamina propria is a layer of loose connective tissue beneath the
epithelium. The muscularis mucosae is a thin layer of smooth muscle; it marks the boundary between the mucosa and the submucosa.
(2)
Submucosa
: dense irregular connective tissue with blood vessels, lymphatic vessels, and
submucosal plexuses (Meissner plexuses)
.
Mucous glands may be present in this layer. (3)
Muscularis externa
: two or three layers of smooth muscle. It may also include skeletal
muscle as in the esophagus. There are blood vessels and
myenteric (Auerbach) plexuses
that lie between the muscle layers. (4)
Serosa/
adventitia
: The outermost layer is called
serosa
if it is composed of loose connective tissue with blood vessels and nerves passing
through and is covered by
mesothelium
. It is called
adventitia
if covered by a layer of connective tissue without mesothelium lining.
The serosa covers organs within the abdominal or pelvic cavities (intraperitoneal), whereas the adventitia covers organs and serves
as a capsule and attachment between the organs or between an organ and the body wall (retroperitoneal).
1. Mucosa
Epithelium
Lamina propria
Muscularis mucosae
2. Submucosa
Mucous glands and lymphatic nodules may be
present
3. Muscularis Externa
Inner circular muscle layer
Outer longitudinal muscle layer
Oblique muscle layer (stomach)
4. Serosa/Adventitia
Serosa: outermost layer composed of connective
tissue
covered by mesothelium
Adventitia: outermost layer composed of connective
tissue
without mesothelium covering
Tunics (Layers) of the Digestive Tract
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