DIGESTIVE SYSTEM
-I-
GENERAL STRUCTURE
of alimentary canal
1) Mucosa 3) Muscularis externa
epithelium 4) Peripheral
lamina propria Connective Tissue
muscularis serosa (visceral
mucosae peritoneum), or
2) Submucosa adventitia
ESOFAGUS
most muscular
segment of GI tract
lumen normally
collapsed by tonus of
muscularis externa,
throwing mucosa into
longitudinal folds
conforms to “typical”4-layered alimentary tube
structure
ESOFAGUS –General structure
3
Mucosa
Epithelium: nonkeratinized stratified squamous
Lamina propria: loose connective tissue;
blood vessels, nerve endings, limphatic vessels
mucosal glands; secret neutral mucus
scattered smooth muscle cells
Muscularis mucosae
Deep layer of longitudinally arranged smooth
muscle
Submucosa
irregular dense connective tissue
contains blood vessels, lymphatic vessels, nerve
tissue ( Meissner plexus)
GLANDS – element of differential diagnosis;
simple tubuloalveolar glands – slightly acid
mucus that lubricates the lumen
excretory duct that pass through the mucosa
to reach lumen
Muscularis externa
2 layers: - inner circular
- outer logitudinal
both striated and smooth muscle, according to
location – element of differential diagnosis
striated muscle – exclusively in the upper one-
thrid
both striated and smooth in the middle one-
third
smooth muscle – exclusively in the distal one-
third
Adventitia
Loose connective tissue that blends with the
general connective tissue of the region
Below diafragm – replaced by serosa
ESOFAGUS –General structure
Mucosa
Stratified squamous epithelium
Lamina propria Sub-
mucosa
Muscularis mucosae
Vessels & Meissner’s
submucosal nerve plexus Muscu-
laris
Inner circular musc.
Outer longi-
tudinal musc. Adventitia
Auerbach’s myenteric
Submucosal esophageal glands
nerve plexus
Esofagus – positive diagnosis
Cavitary organ with a four-layered wall
Muscularis mucosae
Covering epithelium of mucosa: nonkeratinized
stratified squamous
Submucosal glands
Thick muscularis externa, that folds the
supraiacent layers
Presence of striated muscle in muscularis externa
Esogastric junction
Limit between esofagus and stomach
Abrupt delimitation
Endoscopic Z line
STOMACH
Dilated part of GI tract serving as a
reservoir for the accumulation of a
macerated meal received via the esophagus
Stomach – general structure
Gastric pits Mucosa
Gastricglands
Muscularis mucosae
Submucosa
Oblique layer Muscularis
Circular layer externa
Longitudinal layer Serosa
Mucosa
Epithelium:
simple columnar; it lines the surface and the pits
Gastric glands
mucous-secreting cells PAS positive
parietal (oxyntic) cells: acid-secreting
chief cells: protein-secreting
enteroendocrine cells
Stem cells, in the base of gastric pits
Lamina propria
stroma of reticular fibers, fibroblasts and some muscle
fibers
limph nodules and infiltrate of immune cells
Glands of gastric mucosa
Three types:
1) cardiac glands
cardia
2) fundic glands
fundus (= fundus & body of gross anatomy)
3) pyloric glands
pyloric antrum & pylorus
Cardiac glands
almost all cells are
the same, typical of
mucus-secreting
epithelial cells
several glands open
into single gastric
pit
gastric pits
shallow here
(pit/gland
ratio1:1)
Fundic (gastric)
glands
simple, branched tubular
glands
several open into a single
gastric pit
gastric pits shorter, glands
longer
pit/gland ratio 1:4
Pyloric glands
coiled, tubular,
branched glands
cells mostly the same:
like surface mucous
cells
empty into bases of
oblong slits which have
replaced small, round
orifices of gastric pits
elsewhere
pit/gland ratio = 1:1,
but mucosa thickness
greater than in cardia
Summary:
Pit/Gland Ratio
Cardiac mucosa: ~1:1
Fundic mucosa: ~1:4
Pyloric mucosa: ~1:1
but pyloric mucosa is
thicker than cardiac mucosa
Mucosa
Muscularis mucosae: 2 layers of smooth
muscle (inner – circular, outer –
longitudinal)
Submucosa
Dense connective tissue
Meissner plexus
Muscularis externa
3 layers
Auerbach plexux
Distally the circular layer thickens, forming
the pyloric sphincter
Inner – oblique
Middle – circular
Outer – longitudinal
Stomach – positive diagnosis
Tubular organ with four-layered wall
Muscularis mucosae
Covering epithelium: simple columnar
Mucosa – gastric glands that open in gastric pits
No glands in submucosa
Muscularis externa: internal layer with oblique
muscular fibers
SMALL INTESTINE
Mucosa
Submucosa
Muscularis
externa
Serosa
Mucosa
Intestinal villi - finger-like projections into the
lumen (surface epithelium and underlying lamina
propria).
Epithelium - simple columnar heterogeneous
epithelium with goblet cells.
"brush border" (closely-packed microvilli).
absorptive cells - oval nuclei, typically in the
basal half of the cells.
Intestinal mucosa
The lamina propria - loose connective tissue.
blood vessels, nerves, large lymphatic
vessels (site of absorption of lipids), and
cells of the immune system, often in the
form of lymphatic nodules.
Intestinal mucosa
Intestinal glands - simple tubular glands that
open to the intestinal lumen between the base of
the villi (the crypts of Lieberkuhn).
stem cells
immature absorbtive and goblet
enteroendocrine cells
M cells - APCs
secretory cells (Paneth cells) secrete lysozyme
Intestinal epithelium
Submucosa
Valves of Kerckring. The lining of the small
intestine has permanent folds known as Valves of
Kerckring or Plicae circulares. These are most
prominent in the jejunum. These folds, seen
macroscopically in transverse sections, consist of
mucosa and submucosa.
Duodenum: Brunner’s glands
Muscularis externa and serosa
Muscularis externa:
Inner circular layer
Outer longitudinal layer
Serosa – except duodenum- covered by adventitia
DUODENUM
glands in the submucosa (Brunner's glands)
produce alkaline secretions
POSITIVE DIAGNOSIS
four-layered wall
muscularis mucosae
presence of intestinal villi – small intestine
presence of Brunner’s glands : duodenum
ESOPHAGUS STOMACH STOMACH STOMACH DUODENUM
MUCOSA Cardia body antrum
Epithelium stratified sq non-k simple columnar simple columnar simple columnar simple columna
cardial glands pit/ glands=1:1 pit/gland=1:4 pit/gland=1:1
Lamina propria
MM + + + + +
SUBMUCOSA mucous glands mucous glands
MUSC EXT well developed- 2 layers 3 layers 2 layers
ADV/SER adv /ser serosa adv/ser