Chapter 23
The Digestive System
867
23
A thick coating of bicarbonate-rich mucus
builds up on the
stomach wall.
Te epithelial cells of the mucosa are joined together by tight
junctions
that prevent gastric juice from leaking into under-
lying tissue layers.
Damaged epithelial mucosal cells are shed and quickly replaced
by division of
undifferentiated stem cells
that reside where the
Mucosa
Surface
epithelium
Lamina
propria
Muscularis
mucosae
Oblique
layer
Circular
layer
Longitudinal
layer
Serosa
(a) Layers of the stomach wall
Stomach wall
(b) Enlarged view of
gastric pits and
gastric glands
(c) Location of the HCl-producing parietal cells
and pepsin-secreting chief cells in a gastric
gland
Muscularis
externa
(contains
myenteric
plexus)
Submucosa
(contains
submucosal
plexus)
Mucous neck cells
Parietal cell
Pepsinogen
Mitochondria
Surface epithelium
(mucous cells)
Gastric pits
Gastric
pit
Pepsin
Gastric
gland
HCl
Chief cell
Enteroendocrine
cell
Chief cell
Enteroendocrine cell
Parietal cell
Figure 23.15
Microscopic anatomy of the stomach.
hormones that diffuse into the blood capillaries to influence sev-
eral digestive system target organs (
Table 23.1
, p. 868).
Gastrin
, a
hormone, plays essential roles in regulating stomach secretion and
motility, as we will describe shortly.
The Mucosal Barrier
Te stomach mucosa is exposed to some of the harshest condi-
tions in the entire digestive tract. Gastric juice is corrosively
acidic (the H
1
concentration in the stomach can be 100,000
times that found in blood), and its protein-digesting enzymes
can digest the stomach itself.
However, the stomach is not a passive victim of its formida-
ble environment. It mounts an aggressive counterattack to pro-
tect itself, producing the
mucosal barrier
. Tree factors create
this barrier:
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