The mucose membrane lining of gastrointestinal tract is stratified squamous epithelium at the esophagus which slowly convert into simple columnar epithelium at the stomach until the anus it converts back into the stratified squamous epithelium at the lower half of the anal canal. The stratified epithelium is a wear and tear epithelium.
As it passes down from the small to large intestine, goblet cells increase because as it passes down water was absorb, goblet cells function to produce mucous.
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By: Gan Quan Fu, PT, MSc Anatomy
2. General Structure
3. Histology of:
1. Oral Cavity
4. Small Intestine
5. Large Intestine
7. Salivary Gland
9. Gall Bladder
4. Medical Application
Small & Large Intestines
General Structure of Digestive Tract
o Hollow tube composed of a lumen whose diameter
o Surrounded by a wall made up of 4 principal layers:
o Epithelial lining; A lamina propria of loose
connective tissues rich in blood, lymph vessels
and smooth muscle cells; Muscularis mucosae.
o Dense connective tissues with many blood and
o Contains smooth muscle cells, divide into 2
layers; internal (circular); external (longitudinal)
o Thin layer of loose connective tissue rich in
blood and lymph vessels and adipose and
single squamous covering epithelium
Stratified Squamous Epithelium
Protects Oral Mucosa
from damage during
In Gingiva and Hard
Lamina Propria has
several papillae and rest
directly on bony tissue
Covers soft palate, lips,
cheeks and floor of mouth
Lamina Propria has
Papillae, similar to those in
dermis of skin and
diffuse small salivary
• Teeth and Associate Structures
• Mass of striated muscle covered by a mucous
• Muscle fibers cross on another in 3 planes, they are
grouped in bundles, usually separated by
• Dorsal Surface Irregular; Thicker epithelium;
Covered anteriorly by a great number of small
eminences papillae; Separated from anterior two
thirds by a V-shaped boundary.
• Ventral Surface Epithelium on this surface is
Papillae of Tongue
• Filiform Papillae
o Conical Shape
o Numerous and present over entire surface of tongue
o Their epithelium does not contain taste bud and is
• Fungiform Papillae
o Resemble mushrooms (narrow stalk and smooth
surface, dilated upper part)
o Contain scattered taste buds on upper surfaces
o Irregularly interspersed among filiform papillae.
• Foliate Papillae
o Poorly developed in humans
o 2 or more parallel ridges and furrows on the
dorsolateral surface of tongue
o Contain many taste buds
Papillae of Tongue
• Circumvallate Papillae
o 7 – 12 extremely large circular papillae whose flattened
surface extend above other papillae (Papillae surrounded
by deep circular furrows).
o Distribute in the V region at the junction of the anterior
2/3rd and posterior 1/3rd of tongue.
o The epithelium is smooth on the lateral surface of papillae
o Great number of taste buds present along sides of these
• Taste Buds
o Onion shaped structures containing 50 – 100 cells.
o Rests in Basal Lamina
o Apical portion project microvilli that poke through an
opening called taste pore.
o 2types of cells are distinguished in relation to taste buds
• Supporting or sustentacular cells
• Neuroepithelial or gustatory cells
• SUSTENTACULAR OR SUPPORTING CELLS
o Arranged peripherally, curved course, narrow at
each end and broader in the centre appearing
o At both ends the cells surround small openings known
as external and internal pores.
• NEUROEPITHELIAL OR GUSTATORY CELLS
o Distributed between the sustentacular cells long
narrow, having slender red shaped form with a
nucleus in the middle.
o On the free surface, these cells gives rise to short hair
which project into the lumen of the pit.
o The substances to be tasted gets dissolved in the
saliva, stimulate the hairs in the neuroepithelial cells
and the impulses is conducted along the nerves
(sweet, bitter, sour, salty)
• Lined by Stratified non keratinized squamous
epithelium in region continuous with esophagus.
• Lined by ciliated pseudostratified columnar
epithelium containing goblet cells in region close to
• Contains tonsils.
• Mucosa of pharynx also has many small mucous
salivary glands in its lamina propria
• Compose of dense connective tissues.
• Muscular Tube function to transport food stuffs from
mouth to stomach
• Covered by non keratinized stratified squamous
• In general same layers as rest of digestive tract.
• In submucosa groups of small mucous secreting
glands (esophageal glands) secretion facilitated
transport of food stuff and protects mucosa.
• Lamina Propria near stomach groups of gland
(esophageal cardiac gland) secrete mucus
• Distal end muscular layer Only smooth muscle
• Mid Portion Mixture of striated and smooth muscle
• Proximal end Only striated muscle cells
• Portion in peritoneal cavity covered by serosa
• The other portion covered by layer of connective tissue,
adventitia that blends into surrounding tissue.
• Mixed exocrine endocrine gland.
• Divides into 4 regions:
• Fundus and body are identical in microscopic
• Mucosa and submucosa of undistended stomach
lie in longitudinally directed folds known as rugae.
• Consists surface epithelium invaginates to various
extend into lamina propria forming gastric pits.
• Lamina propria of stomach composed of loose
connective tissue interspersed with smooth muscle
and lymphoid cells.
• Muscularis mucosae to separate mucosa from
• Epithelium lining the pits and covering the surfaces
are simple columnar epithelium & all cells secrete
• Mucosa contains simple or branched tubular
• Terminal portion of these glands are frequently
coiled, often with large lumens.
• Similar in structure to cardiac glands of the terminal
portion of esophagus.
Stomach (Fundus & Body)
• Simple columnar surface epithelium extends into gastric
pits into which opens into gastric glands.
• Lamina propria consist of fine reticular and collagen
fibres fills the spaces between the packed gastric
• Each gastric gland has 3 distinct region:
• Isthmus contains differentiating mucous cells and
undifferentiated stem cells and parietal cells.
• Neck consist of stem, mucous neck and parietal cells.
• Base contains parietal and chief (zymogenia) cells.
• The muscularis mucosa composed of inner circular and
outer longitudinal smooth muscle.
• Deep gastric pits into which the branched tubular pyloric
• The epithelium of the mucous membrane consist of tall
columnar cells which lines the deep pits and short glands.
• Longer pits and shorter coiled secretory portion compare
to glands in cardiac region.
• The acini of pyloric glands and their ducts are in lamina
• G (Gastrin) cells are enteroendocrine cells intercalated
among mucous cells of pyloric glands.
• D cells secrete Somatostatin
• The muscularis externa is made up of thick circular muscle
to form pyloric sphincter which helps to control emptying
of the stomach.
• 4 layers:
3. Muscularis externa
• Surface area of small intestine increased by
1. Length of small intestine
2. Valves of Kerkring/ Plica Circularis
5. Cypts Of Lieberkuhn
Valves of Kerkring
• Also known as Plica
• Permanent submucosal
• Large, seen with naked eye
• Prominent in duodenum &
• Less marked in ileum
o Increases surface area
o Slow down the passage
• Central lacteal (lymphatic
• Core capillaries
• Core of connective tissue
• Epithelial cells – Tall
columnar with striated
Crypt of Lieberkuhn
• Invaginations of lining
epithelium into lamina
• Wall of crypt is lined by
the following cells:
1. Columnar cells
2. Goblet cells
3. Undifferentiated stem
4. Paneth / Zymogen
5. Argentaffin cells
Crypt of Lieberkuhn
• Absorptive columnar
cells / Enterocytes
o Microvilli which give
it a striated border
• Goblet cells
o Secretes mucus
• Undifferenciated cells
o Actively multiply,
move upwards give
rise to other cells
Crypt of Lieberkuhn
• Paneth cells / Zymogen cells
o Seen in deeper parts of crypts
o rich in Zinc, secrete lysozyme that destroys
• Endocrine cells
o Seen near lower ends of crypts
o Argentaffin cells
o Entero-chromaffin cells
o APUD cells – secrete serotonin
• In duodenum (Also known as duodenal glands)
• Clusters of ramified, coiled tubular glands that
opens into the intestinal crypts.
• Cells are mucous type.
• Secretions are distinctly alkaline (PH8.1 – 9.3), to
protect duodenal mucous membrane from effects
of acid gastric juice and to brings intestinal contents
to optimum PH for pancreatic enzyme action.
• Lymphoid Nodules.
• Present in ileum, more
prominent in terminal ileum.
• In lamina propria and
• Dome shaped area devoid of
• Instead of absorptive cells, its
covering epithelium consist M
Differences between duodenum,
jejunum & ileum
Duodenum Jejunum Ileum
Few goblet cells
Few thin finger-
Lamina Propria Crypts+
Submucosa Mucus secreting
• Consists mucosal membrane with no folds except in
its distal (rectal) portion.
• No vili are present
• Long intestinal glands
• Great abundance of goblet and absorptive cells
• Small number of enteroendocrine cells.
• Fibers of outer longitudinal layer congregates in 3
thick longitudinal band (Teniae coli).
• Serous layer characterized by small, pendulous
protuberances composed adipose tissues
• Mucous membrane forms a series of longitudinal
folds (rectal columns of morgagni)
• Evagination of cecum
• Small, narrow and irregular lumen caused by
presence of abundant lymphoid follicles in its wall.
• Although general structure similar to large intestine,
it contains fewer and shorter intestinal glands and
has no teniae coli.
Small Vs Large Intestine
Small intestine Large intestine
Villi 1. Crypts shallow
2. Goblet cells less
1. Absence of villi
2. Crypts deeper,
1. Uniformly thick 1. Three bands of
• Serous cells
o Pyramidal in shape
o Broad base resting on basal lamina
o Narrow apical surface with short irregular microvilli
o Secretory cells are joined together by junctional
complex and usually form spherical mass of cells
• Mucous Cells
o Usually cuboidal to columnar
o Oval nuclei pressed towards bases of the cells
o Most often organized as tubules, consisting of
cylindrical arrays of secretory cells surrounding a
• Duct System
o Intralobular ducts
• Intercalated Ducts
o Lined by Cuboidal Epithelial Cells
o Ability to differentiate into secretory or ductal cells
• Striate Ducts
o Radial striations seen to consist infoldings of basal
plasma membrane with numerous elongated
o Drains into Interlobular Ducts
o Interlobular Ducts (Excretory Ducts)
• Initially lined with pseudo stratified or stratified cuboidal
• Distal parts lined with stratified columnar epithelium
consisting few mucus secreting cells
• Ultimately empties into oral cavity and lined by
nonkeratinized-stratified squamous epithelium.
• Parotid Gland
o Branched acinar glands
o Surrounded by a capsule from which arise numerous
interlobular connective tissue septa that subdivides
the gland into many lobes and lobules.
o Located in the connective tissue septa between the
lobules are arteriole, venule and interlobular
• Submandibular Gland
o Presence of both serous and mucous acini.
o Mucous acinus are larger than the serous.
o Between the mucous cells and basement membrane
are half moon shaped granules known as demilunes
• Sublingual Gland
o Similar as Sub mandibular
o Intralobular ducts are not as well developed as in
other major salivary gland
• Repeating hepatic lobules (Hexagonal Unit).
• Central Vein in the centre of each hepatic lobule.
• Portal canals (Portal Traids) in periphery the surrounding
connective tissue [Branches of the hepatic artery,
hepatic portal vein, bile duct, and lymph vessels seen.]
• Hepatic sinusoids (dilated blood channels) contains
epithelial cells and macrophages called “Kupffer cells”
• The hepatic sinusoids separated from the underlying
hepatocytes by subendothelial perisinusoidal space of
• The major exocrine functions of hepatocytes is synthesis
and release about 500-1200ml of bile per day which is
delivered to the gallbladder via the bile canaliculli.
• It consist of mucosa composed of Simple columnar
epithelium and lamina propria; a layer of smooth
muscle; a perimuscular connective tissue layer and
a serous membrane.
• Mucosa has abundant folds that are particularly
evident when gall bladder is empty.
• Epithelial cells are rich in mitochondria
• Surrounding the bundle of smooth muscle fibres is a
thick dense connective tissue containing large
blood vessels artery & vein, lymphatic and
• Serosa covers entire unattached gallbladder
• Mixed endocrine and exocrine gland
• Exocrine compound acinar gland, similar in
structure to parotid gland.
• Distinction between 2 glands can be made based
on absence of striated ducts and presence of islets
• Initial portions of intercalated ducts penetrate
lumens of acini.
• Centroacinar cells constitude interacinar portion of
• Gastroesophageal Reflux Disease associated with
incompetent barriers at gastroesophageal junction
caused by decrease in lower esophageal sphincter
tone or hiatus hernia. Reflux esophagitis develops
when mucosal defenses are not sufficient to protect
esophageal mucosa from acid, pepsin and bile.
• Stress, ingested aspirin, NSAID or ethanol can disrupt
epithelial layer in stomach lead to ulceration. Ulcer
is disruption of mucosal integrity leading to an
excavation due to active inflammation. Apirin and
ethanol irritates mucosa partly by reducing blood
• Junquiera, L. C. (2005) Basic Histology text & Atlas,
11th edn. McGraw Hill, New York.