1. DIGESTIVE
TRACT
Department of Histology, Cytology and Embryology
Tatiana Globa
State University of Medicine and Pharmacy “Nicolae Testemitanu”

3. BASIC PLAN OF THE DIGESTIVE TUBE
Four functional layers:
 Tunica mucosa: This layer is composed of epithelium, connective
tissue and muscle. These tissues can usually be found in distinct
layers as follows:
 lamina epithelialis mucosae: consists only of epithelium
 lamina propria mucosae: consists of either loose areolar or reticular
connective tissue
 lamina muscularis mucosae: consists of smooth muscle
 Tunica submucosa: consists of loose connective tissue, nerves, blood
vessels, and glands in some organs
 Tunica muscularis: consists of at least two layers, an inner circular
and an outer longitudinal with parasympathetic ganglia located
between the layers
 Tunica adventitia or tunica serosa: consists of loose connective
tissue.

5. Esophagus:
 The esophagus connects the
oral cavity with the stomach
allowing and aiding in the
movement of food particles
to the stomach.
 It is a muscular tube having
the layers described above
for the typical tubular organ.
 In the esophagus the layers
are specialized for the
function of further
fragmenting food particles.

6. Layers of the esophagus
 Tunica mucosa:
epithelium: consists of stratified squamous epithelium that
can be highly folded in an empty organ;
lamina propria: consists of loose connective tissue,
contains esophageal cardiac glands that are simple
branched tubular glands, they produce mucus, mucin,
chlorides and some biologically active substances.
lamina muscularis mucosae: consists of longitudinally
oriented smooth muscle fibers that form 1 layer (can be 2)
 Tunica submucosa: consists of loose connective tissue that is
very elastic allowing for expansion when food is present;
contains esophageal glands proper; they are compound
tubuloalveolar glands, which produce mucous.

7. Layers of the esophagus
 Tunica muscularis: consists of smooth and/or skeletal
muscle;
Proximal end – skeletal muscle cells
Middle region – skeletal plus smooth muscle
Distal end – smooth muscle cells
inner circular layer
outer longitudinal layer
 Tunica adventitia/serosa: consist of typical loose
connective tissue that blends into the connective tissue of
surrounding tissues. Serosa: only at distal end that enters
peritoneal cavity.

8. Esophageal wall

9. STRATIFIED SQUAMOUS
EPITHELIUM
LAMINA PROPRIA
LAMINA MUSCULARIS

10. Esophageal
glands proper
(submucosal,
tubuloalveolar
glands;
acidic mucus
secretion)
Esophageal
cardiac glands
not shown
Present in lower
portion; tubular
mucosal glands
produce mucus with
neutral pH

12. Gastro-Esophageal junction

13. Comparative characteristic of the wall structure of
esophagus and stomach
Esophagus Stomach
Mucosa
Epithelium
Stratified squamous nonkeratinized Simple columnar glandular
Lamina propria of mucosa
Contains esophageal cardiac glands that
are simple branched tubular glands.
They produce mucus, mucin, chlorides
and some biologically active substances.
Contains gastric glands that are simple
branched tubular. Differ 3 groups of
glands:
1. cardiac glands in the cardiac region
2. pyloric glands in the pyloric region
3. fundic or gastric glands in the fundic
region.
Muscularis mucosae
Consists of longitudinally oriented
smooth muscle fibers that form 1 layer
(can be 2)
Consists of 3 layers of smooth muscle:
Inner – circular
Middle – longitudinal
Outer – circular

14. Submucosa
Contains esophageal glands proper.
They are compound tubuloalveolar
glands, which produce mucous.
Glands are absent.
Muscularis externa
In the upper one-third – is striated
muscle.
In the middle one-third – is striated
and smooth muscle.
In the distal third – is smooth as in
rest of the digestive tract.
It forms 2 layers: inner – circular;
outer – longitudinal
Present only smooth muscle that
forms 3 layers:
Inner – obligue;
Middle – circular;
Outer – longitudinal.
Between the muscle layers is present
Auerbach’s plexus
Superficial tunica
In the thoracic cavity is adventitia.
After entering the abdominal cavity is
serosa.
Serosa is present.

15. STOMACH

16. STOMACH
 Structure - 4 Regions
 Cardia
 Fundus
 Body
 Pylorus
 Functions:
 Continue digestion of carbohydrates started in mouth
 Add acidic fluid
 Transform food into chyme (mechanical & chemical
breakdown)
 – Promote initial digestion of proteins (via pepsin) and
triglycerides (via lipase)

17. STOMACH
 Cardiac region – surrounds the cardiac
orifice
 Fundus – dome-shaped region beneath the
diaphragm
 Body – midportion of the stomach
 Pyloric region – made up of the antrum and
canal which terminates at the pylorus
The pylorus is continuous with the duodenum
through the pyloric sphincter

18. The inner surface of
the stomach is
irregular. There are:
• Rugae – are
longitudinally
oriented folds
• Gastric (mamillated)
areas – are bulging
irregular areas
• Gastric pits – funnel-
shaped depressions.
Gastric glands empty
into the bottom of the
gastric pits

19. GASTRIC PITS

21. Layers of the TUNICA MUCOSA
 Epithelium: consists of simple columnar epithelium that
forms branched, tubular glands; organized into gastric pits
that open onto the lumen and gastric glands that empty
into the base of the gastric pits
 Lamina propria: consists of loose areolar connective
tissue that in the glandular stomach is minimal between
gastric glands and difficult to see in sections; highly
vascular containing many blood and lymphatic capillaries
 Lamina muscularis mucosae: consists of several layers
of smooth muscle oriented both longitudinally and
circularly; usually not very thick

23. STOMACH
 Tunica submucosa: typical loose connective tissue
contains submucosal plexuses also known as
Meissner's plexuses
 Tunica muscularis: 3 layers of smooth muscle
 Outer longitudinal
 Middle circular
 Inner oblique
 between the muscle layers is located the myenteric or
Auerbach's plexus
 Tunica serosa: small amount of loose connective
tissue with overlying simple squamous epithelium or
mesothelium

25. Epithelium
simple
columnar
glandular
of the
stomach
mucosae
Gastric
glands
simple
tubular
few
branched

26. Glands of the Stomach Fundus and Body
 Mucous neck cells – found dispersed between the parietal cells; secrets a
mucus that is thinner than that secreted by the surface mucous cells; mucus
protects other glandular cells from action of proteases and HCl.
 Parietal cells (oxyntic cells) – found throughout the gastric gland; round
cells that contain distinct eosinophilic (pink) cytoplasm and round, prominent
nucleus; Secrete HCl and intrinsic factor, needed for absorption of vitamin
B12 in the ileum.
 Chief cells (zymogenic cells) – found mostly near the base of the gastric
glands; very basophilic (purple) containing basally positioned nucleus and
prominent basophilic apical cytoplasm filled with many ribosomes; secrete
pepsinogen, which is activated to pepsin by HCl in the stomach. Pepsin is an
enzyme which is able to break down proteins.
 Endocrine cells – difficult to distinguish by conventional light
microscopy; Several types are present; some secrete gastrin, glucagon and
somatostatin, histamine, endorphins, serotonin, cholecystokinin (CCK)
among other hormones.
 Undifferentiated cells – located primarily in the neck region; difficult to
identify in routine H&E sections; undergo mitosis to form more cells then
differentiate into the other cell types present in the gland

28. Chief cells (basophilic)

29. Chief cell
Pepsinogen
on the apical
part of the
cell

30. Parietal cells (red color)

31. Parietal cell
Intracellular
canalicular system
Mitochondria

32. Endocrine cells
Type:
G-cells – gastrin – is the
principal agent for stimulating
the secretion of HCl and
pepsinogen
D-cells produce somatostatin.
They inhibit G-cells
EC-cells produce serotonin and
substance Р which increase
stomach activity.
ECL-cells produce histamine
which regulate gastric secretion

33. Cardiac glands
Cardiac glands are tubular, occasionally
branched glands (similar to the cardiac glands
of the esophagus), which contain mainly
mucus-producing cells. A few of the secretory
cells characteristic for the corpus-fundic
glands (chief and parietal cells) may be
present.

34. Pyloric glands
Pyloric glands are more coiled than corpus-
fundic glands, and they may be more branched.
The lumen is relatively wide. A few parietal cells
may be present but chief cells are usually absent.

35. Shallow gastric
pits, with simple or
branched tubular
glands
Shallow gastric
pits, with branched
tubular glands
Deep gastric pits,
with branched
tubular glands

37. SMALL INTESTINE
 Is the longest component of the digestive tract
 Is divided into three anatomic segments:
duodenum, jejunum, and ileum
 Functionally, it is the principal site for the
digestion of food & for absorption of the
products of digestion
 Endocrine Secretion
 The bile duct and main pancreatic duct:
 Join the duodenum at the hepatopancreatic ampulla
 Are controlled by the sphincter of Oddi

38. SMALL INTESTINE
Specializations of intestinal surface
 Plicae circulares: deep circular folds of the mucosa
and submucosa, most abundant in jejunum
 Villi – finger-like projections of the mucosa that
extend into the intestinal lumen (epithelium plus lamina
propria)
 Intestinal crypts (glands of Lieberkühn) – are
simple tubular glands between villi
 Microvilli – numerous projections of apical plasma
membranes of absorptive mucosal cells and give the
apical region of the cell a striated appearance,
called striated border (brush border)

39. Plicae circularis

41. Crypts
Villi

43. Villi
• Finger-like
projections of
mucosa
• Contain:
- fenestrated
capillary network
- a central, blind-
ending lymphatic
capillary (lacteal)
- few smooth muscle
cells derived from
muscularis
mucosae
- myofibroblasts
• Are covered by
intestinal
epithelium – simple
columnar

45. SMALL INTESTINE
Layers of the Small Intestine
 Tunica mucosa:
 Epithelium - simple columnar
 Lamina propria - loose connective tissue rich in blood and
lymphatic vessels present in the core of the villi and between
crypts
 Lamina muscularis mucosae - thin layer of smooth muscle
located at the base of the crypts
 Tunica submucosa: This layer blends with the lamina propria and
is typical. In the duodenum it has coiled branched glands known as
Brunner's glands, the ducts of which open into the base of the crypts.
 Tunica muscularis: typical consisting of an inner circular layer and
an outer longitudinal layer
 Tunica serosa: typical

46. The epithelium of the villus
 Enterocytes (absorptive
cells)
 Goblet cells –
unicellular mucin-
secreting glands,
increase in number from
the proximal to the distal
small intestine
 Enteroendocrine cells
resemble those
described in the stomach

47. Epithelium lining the
small intestine –
simple columnar

48. The epithelium of the crypt
 Enterocytes (absorptive cells)
 Goblet cells
 Enteroendocrine cells
 Paneth cells – are found in the bases of
the glands. They have a basophilic basal
cytoplasm & large, intensely acidophilic
apical secretory granules. These granules
contain: the antibacterial enzyme lysozyme
(digests the cell walls of certain groups of
bacteria), glycoproteins, an arginine-rich
protein & zinc. The antibacterial action & the
phagocytosis of certain bacteria & protozoa
by Paneth cells suggest that they have a role in
regulating the normal bacterial flora of the
small intestine.
 Undifferentiated cells

52. Goblet cell

53. Gut-Associated Lymphatic Tissue
 Lymphatic nodules
 Lymphocytes
 Macrophages
 Plasma cells
 Eosinophils
 GALT serves as an immunologic barrier

54. Regional variations in the small
intestine:
DUODENUM
 presence of Brunner's glands in the submucosa -
compound tubuloalveolar branched glands, mixed
glands
 presence of chyme in the small intestine induces
cells of Brunner's glands to secrete alkaline mucus
that neutralizes gastric acid and pepsin and
further promotes digestion
 no plicae circulares

57. Regional variations in the small
intestine:
JEJUNUM
 no glands in the submucosa
 longest villi of all three regions
 no lymphoid nodules

60. Regional variations in the small
intestine:
ILEUM
 permanent aggregated lymphoid nodules in the
submucosa
 shortest villi
 highest number of goblet cells

63. LARGE INTESTINE
 Regions
 Cecum – Appendix
 Colon
 Ascending
 Transverse
 Descending
 Rectum
 Anal canal
 Functions:
 Reabsorption of electrolytes & water
 Formation of waste
 B vitamins & vitamin K synthesized

64. LARGE INTESTINE
Unlike the small intestine, there are no plicae circulares or villi
in the large intestine so the surface of the tunica mucosa is
more uniform and flatter than that of the small intestine.
 Tunica mucosa:
 epithelium - simple columnar epithelium that forms straight tubular
glands (crypts)
 lamina propria- loose connective tissue that contains numerous blood
and lymphatic vessels, collagen, lymphocytes and plasma cells
 lamina muscualris mucosae- present beneath the base of the crypts and
prominent; undergoes rhythmic contractions
 Tunica submucosa: typical, contains Peyer’s patches which
are aggregations of solitary follicles or groups of lymph
nodules. Each pach contains from 10 to 70 nodules

65. The epithelium of the crypt
 Goblet cells – are
more numerous than
in the small intestine
 Enterocytes
(absorptive cells) - few
 Enteroendocrine cells
 Undifferentiated cells

66. Colon crypts

68. LARGE INTESTINE
 Tunica muscularis: inner circular and outer
longitudinal layers; outer longitudinal layer is organized
into three separate bands known as taenia coli; movement
of more solid waste to the rectum
 Tunica serosa is typical.
Commensal bacteria reside in the large intestine and play a role in the
continued digestion of food.

70. Appendix

72. Colorectal Zone
(simple columnar
epithelium, crypts)
Anal Transition
Zone
(stratified
columnar/cuboidal
epithelium)
Squamous Zone
Pectinate line