f. Stomach
• (1) General features
• a) Stomach is widened portion of gut-tube: between tubular and spherical;
Note arranged of smooth muscle tissue in muscularis externa.
1
f. Stomach
•
(b) Stomach’s function
• 1. Dilution of food
materials
•
•
2. Acidification of
food (absorption
of dietary Fe in
small intestine)
3. Partial chemical
digestion of
proteins
•
continued
digestion of
carbohydrates
2
f. Stomach
•
•
4. Little to no absorption
under normal conditions
• a. Can absorb glucose
• b. Absorbs ethanol
• c. Absorbs Na+ and K+, but
only if levels of these ions
are subnormal
• d. Absorbs water when
body dehydrated and
osmotic pressure
abnormally high and blood
volume and pressure
unusually low.
5. Formation of acidic chyme:
• Mixture of acidic gastric
juice and food
3
f. Stomach
•
(c) Mucosa: very folded; folds longitudinally oriented and called rugae.
• 1. Lumenal epithelium: simple columnar epithelium: secretes mucus;
cytoplasm tends to be acidophilic; cells lack microvilli.
•
2. Lumenal surface has abundant pits: funnel-like depressions that lead to
the mucosal glands; pits vary in steepness and depth from one region of
organ to another.
4
f. Stomach
•
3. Mucosal glands common
• compound (branched)
tubular glands
extending into deeper
parts of mucosa, from
pits; not acinar
• wall of gland one cell
thick
• 4 possible cell
types
• mucous cells
• parietal cells
•
•
chief (principal;
peptic) cells
endocrine cells
(G cells).
5
• a. Except for endocrine
•
•
f. Stomach
.
cells, restricted to one
region of stomach, glands
are exocrine, secreting
fluid into lumen of stomach
b. All cells of wall of gland
are glandular cells.
c. Uppermost part of gland,
continuous with epithelium
of pit; neck of gland
• neck composed of low
columnar mucus cells not as eosinophilic as
lumenal epithelial cells
• mucus neck cells.
6
f. Stomach
•
d. Below neck of gland,
cells include the other 3
types .
• (1) Parietal cell:
large, spherical,
eosinophilic,
sometimes granular
cytoplasm; secretes
HCl: acidification of
the food; often
found in upper part
of gland.
7
8
9
f. Stomach
•
•
•
(2) Chief (principal; peptic) cell
• tends to be in lower part ,
• narrower than parietal cell
• cytoplasm basophilic
• nucleus toward basal side of cell
• very active in protein synthesis:
produces and secretes
pepsinogen
• zymogen of pepsin: enzyme that
breaks protein molecules into
chains of several to many amino
acid residues.
(a) Chief cells therefore are
zymogenic cells.
(b) Pepsinogen converted to pepsin in
lumen of gland and in lumen of organ.
10
11
f. Stomach
•
(3) Endocrine cells: specifically
gastrin cells, for the hormone they
produce and release
• restricted to deepest parts of
glands of one region of
stomach.
• A subset of enteroendocrine
cells;
•
•
>12 types
gastrin, histamine, endorphins,
serotonin, cholecystokinin,
somatostatin
12
f. Stomach
•
4. Muscularis mucosae
• present, composed of
smooth muscle tissue, often
in 3 layers;
•
•
has numerous thin
extensions up into lamina
propria.
MM
5. Lamina propria
• composed of unusually
cellular dense C.T. with
capillaries, arterioles,
venules, lymphatic
capillaries, small nerves; all
of these but capillaries very
difficult to detect
13
f. Stomach
•
(d) Submucosa
• 1. Extends up into rugae.
• 2. Mostly dense C.T
• small muscular
arteries, small veins,
smaller blood
vessels, small
lymphatic vessels,
small masses of
neural tissue and
sometimes clumps of
adipocytes
• areas of loose C.T.
may be present also.
Mucosa
Submucosa
MM
Muscularis
externa
14
f. Stomach
•
(e) Muscularis externa of
stomach
• 1. Normal Inner-circular,
outer-longitudinal
organization partially lost:
smooth muscle tissue is in
large slabs oriented in a
variety of directions, some
remnant of inner-circ.,
outer-long pattern usually
detectable.
Inner
circular
Outer
longitudinal
15
f. Stomach
•
2. Myenteric plexus usually
detectable; its location
indicates the original
interface between inner-circ,
outer-long layers.
•
3. This organization of
smooth muscle tissue relates
to the organ's shape.
4. Muscularis is, overall,
relatively thick and powerful.
•
Myenteric plexus
16
f. Stomach
•
(f) Tunica adventitia
• 1. T. adventitia of
stomach is distinct layer
with an outer,
mesothelium, covering.
• 2. T. adventitia composed
of dense C.T. and loose
C.T. and contains larger
blood vessels and nerves
than those found in
submucosa.
T.adventitia
17
f. Stomach
•
g) Stomach regions
• divided into 4 regions; in most
cases these regions differ in
mucosal structure only.
•
1. Cardiac region: small region
adjacent to cardiac sphincter.
•
2. Fundic region (fund: root
meaning deep): one side of
upper part of organ.
3. Body: most of organ.
4. Pyloric region: lower end,
adjacent to pyloric sphincter.
•
•
18
f. Stomach
•
2) Special features of region
of stomach
(a) Cardiac region
• 1. pits; intermediate depth
and cardiac glands are
almost entirely mucus cells
•
2. Glands sometimes not as
densely packed as in other
regions.
19
20
•
f. Stomach
(b) Fundic region and body (no histological differences between them)
• 1. Pits relatively shallow (because fluid secreted by glands is nonviscous)
•
2. Gastric glands densely packed; C.T. of lamina propria not obvious.
• Neck of gland composed of mucus neck cells; other cells of gland
parietal cells and chief cells
21
f. Stomach
•
(c) Pyloric region
• 1. Pits deep
• half the depth of the
mucosa
• Gland composed of mucus
cells ;look like mucus neck
cells
• diameter of gland's lumen
high, due to high viscosity
of secreted fluid
• Called pyloric glands.
22
23
f. Stomach
•
a. Pyloric region and cardiac region; major function; mucus
production;
• mucus coating of the lumenal epithelium
•
•
•
protection from acidity and proteolytic action of gastric
juice.
If mucus layer becomes thin or lost, the pepsin and HCl in
the lumen will destroy the lumenal epithelium of that area
and perhaps begin destroying the glands and C.T. of the
lamina propria
Called a peptic ulcer.
24
f. Stomach
•
b. Lower parts of the pyloric glands ; cells are mainly endocrine; with H&E
staining they are not distinguishable from mucus cells
• gastrin endocrine cells
•
•
•
•
produce the hormone gastrin,
controls gastric glands
gastrin is released to the capillaries of the lamina propria rather
than to the lumen of the gland.
c. Overall length of glands relatively great
25
f. Stomach
•
•
3. Mucosa unusually thick overall; staining relatively pale.
4. Pyloric region ends at pyloric sphincter; between stomach
and duodenum
•
sphincter itself is a thickened region of inner, circular
layer of muscularis externa.
26
`
Regions
Cardiac
Pits
Intermediate
depth
Glands
Gland
cells
Function
Not
densely packed
obvious lumen
Mucus
Fundus/
body
Pyloric
Shallow
Deep, at least 1/2 of
mucosa
with wide lumen
Densely packed
Not
densely packed
obvious lumen
Mucus, parietal, chief,
Mucus
enteroendocrine cells enteroendocrine cells
(not visible w H&E)
(not visible w H&E)
Protection of
Protection of
Production of gastric
juice;
cardiac region and
pyloric region
distal esophagus Hormone regulation Hormone regulation
27