This document provides information on the structure and layers of the digestive tract, including the esophagus, stomach, small intestine, and large intestine. It details the four functional layers that make up the basic plan of the digestive tube: the tunica mucosa, tunica submucosa, tunica muscularis, and tunica adventitia/serosa. For each organ, it describes the epithelium, glands, muscle layers, blood vessels, and other distinguishing characteristics. The purpose is to concisely summarize the histological features and organization of the digestive system.

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

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. 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

8. 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.

9. Esophageal wall

10. STRATIFIED SQUAMOUS
EPITHELIUM
LAMINA PROPRIA
LAMINA MUSCULARIS

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 Contains gastric glands that are simple
are simple branched tubular glands. branched tubular. Differ 3 groups of
They produce mucus, mucin, chlorides glands:
and some biologically active substances. 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 Consists of 3 layers of smooth muscle:
smooth muscle fibers that form 1 layer Inner – circular
(can be 2) Middle – longitudinal
Outer – circular

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

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

20. 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

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

24. 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

26. Chief cells (basophilic)

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

28. Parietal cells (red color)

29. Parietal cell
Intracellular
canalicular system
Mitochondria

30. 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

31. 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

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
Deep gastric pits, Shallow gastric
with branched pits, with branched
tubular glands 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
circulares
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

40. Villi
Crypts

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. Epithelium lining the
small intestine –
simple columnar

47. 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

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:
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:
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
submucosa
are aggregations of solitary follicles or groups of lymph
nodules. Each patch contains from 10 to 70 nodules.

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

67. 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. Between
the taenia coli there is an thin sheet of longitudinal smooth muscle.
 Tunica serosa is typical.
Commensal bacteria reside in the large intestine and play a role in the
continued digestion of food.

70. Appendix
- Includes a complete layer of
longitudinal smooth muscle.
- Contains a large number of lymph
nodules positioned in both the
mucosa and the submucosa.
- The muscularis mucosa appear as
isolated lengths of smooth muscle.

71. - is the terminal portion of the alimentary canal
Anal
sinuses

72. Colorectal Zone
(simple columnar
epithelium, crypts)
Anal Transition
Zone
(stratified columnar/cuboidal
epithelium, anal glands
extend into the submucosa)
Pectinate line
Squamous Zone