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HISTOLOGY OF THE GIT (ONE)
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The human gastrointestinal
tract
• The human gastrointestinal tract, or GI tract, or
GIT is an organ system responsible for
consuming and digesting foodstuffs, absorbing
nutrients, and expelling waste
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Oral Cavity
• The oral cavity is bound by
lips anteriorly and chicks
laterally, and it contains the
tongue and the teeth
supported by periodontium.
• The palate forms its roof
and posteriorly the mouth
communicate with the
oropharynx through the
oropharyngeal isthmus
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•
•
•
The lips
Each lip is lined by skin on the outside and on the inside is lined by
mucous membrane.
The red free margins of the lips do not contain sweat or sebaceous
glands or hair follicles. These margins of the lips are covered with a
modified skin which represents a transition from skin to mucous membrane.
Its dermis has numerous blood vessels; as a result the blood in the
capillaries readily shows through the transparent epidermis to make the lips
appear red.
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…the lips
• Internally the lips are covered by a mucous membrane
consists of stratified squamous non-keratinising
epithelium lying upon a connective tissue lamina propria.
The connective tissue that contains small mucous glands
(labial glands) and nerve endings.
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Like the parotid and buccal glands, the labial glands are innervated
by parasympathetic fibres that arise in the inferior salivatory
nucleus, travel with the glossopharyngeal nerve and lesser petrosal
nerve to the otic ganglion, where they synapse and then continue to
the labial glands
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Salivary Glands
• There are three pairs of large salivary glands they
include:
1. The parotid,
2. Submandibular, and
3. sublingual glands.
The function of these glands is to secrete saliva which
enters the oral cavity via the ducts.
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The parotid glands
• There are two of them each located below and anterior
to each ear, between the ramus of the mandible and the
mastoid process. The main duct of the parotid, the
Stensen’s duct opens into the oral vestibule adjacent to
the maxillary second molar tooth.
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… parotid
(histological features)
• The gland is a compound tubuloalveolar of
serous type.
• A dense fibroelastic capsule encloses the gland,
which is part of the investing layer of the deep
cervical fascia.
• The parenchyma of the glands consists of secretory
end pieces (the acini) and a branching duct system
arranged in lobes & lobules, separated by septae
of connective tissue originating from the capsule
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… parotid
(histological features)
• The acini are made up of serous cells which are
pyramidal in shape with basal nuclei. The basal
and perinuclear cytoplasm is basophilic and the
apical contains secretory glanules.
• The duct system is divided into intralobular and
extralobular ducts.
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Intralobular ducts
• Intralobular ducts are contained within the lobules
and they include the intercalated ducts and
striated ducts.
• The intercalated ducts represent the first duct
system and they originate from the acini. They are
lined by simple cuboidal epithelium.
• Striated ducts are large ducts in diameter and are
lined by columnar cells that has microvilli on their
apical surface.
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The extralobular ducts
• The extralobular
ducts are large and
include the excretory
ducts and the main
duct, the Stensen’s
duct which is lined by
stratified columnar
cells.
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The submandibular gland
• It is a compound tubuloalveolar gland with mixed but mainly
serous and few mucous acini.
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…submandibular gland
• The duct system differs from the parotid gland in that it has
short intercalated ducts this makes them less prominent.
• The epithelium of the interlobular ducts is lined by
pseudostratified epithelium with few goblet cells, which
modify the saliva by addition of mucous.
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…submandibular gland
• Its main ducts are known as Wharton’s duct and opens into
floor of the mouth underneath the tip of the tongue.
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Sublingual gland
• This is not a single gland but a collection of small
groups of mixed glands, which are predominantly
mucous in nature. It lies in the floor of the mouth
over the mylohyoid muscle.
• The main ducts from sublingual glands may
open together with the main duct of the
submandibular gland. The duct system is less
prominent because they are short and not well
demonstrated in histological sections.
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Sublingual gland…
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The cheek
• Has an outer covering of skin and inner lining of
mucous membrane, similar to that of the lips. Superficial
cells are constantly being rubbed off the surface and
replaced from below.
• There are small mucous glands in the lamina propria of
the cheek.
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The palate
• The palate is described to have hard palate and soft
palate.
• The hard palate consists of a stratified squamous
epithelium supported by a lamina propria that tightly
adheres to the periosteum of the bone.
• Its stratified squamous epithelium is keratinized to a
variable degree. A number of mucous glands are also
present
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…the palate
• The soft palate consists of central skeleton of
dense fibrous tissue (palatine aponeurosis).
• The soft palate has two surfaces, the oral and nasal.
The oral and lower part of the nasal surfaces are
lined by stratified squamous non-keratinized epithelium.
The lining of the rest of the nasal surface is covered by
pseudostratified ciliated columnar epithelium.
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The tooth
• A tooth is made up of the following structures:1.Enamel
2.Dentin
3.Pulp Cavity
4.Cementum
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The Enamel
• White (translucent), hard and resistant layer
covering the crown of the tooth, protecting the tooth
from mechanical and chemical attack.
• Made up of enamel rods that run parallel to each
other, projecting perpendicularly from the dentin
surface.Each enamel rod attaches directly to the
dentin underneath, preventing penetration of cracks
in the enamel into the dentin.
• Enamel meets the dentine at the enamel-dentin
junction (EDJ) and meets the cementum at the
cemento-enamel junction (CEJ)
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The Dentin
• Hard, yellowish material that lies underneath the
enamel, surrounding the pulp chamber of the tooth.
Sensitive to stimuli (even though it is not innervated) due to
movement in fluid in the odontoblast projections in
dentin tubules originating from the inner surface of the
dental pulp perpendicularly outwards to the tooth surface
until just before the enamel.
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Pulp Cavity
• Dental pulp is a pink and soft organ consisting
connective tissue, blood vessels and nerve
axons.
• Is the central hollow structure composed of loose
connective tissue with the blood vessels and
odontoblasts, which are dentine forming cells that
form a layer on the periphery of the pulp, thus
lines the inner surface of the dentine.
• Involved in dentinogenesis (the process of
building dentin)
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…dental pulp
Zones of the Pulp
1. Cell rich zone; innermost pulp layer which
contains fibroblasts and undifferentiated
mesenchymal cells.
2. Cell free zone (zone of Weil) which is rich in
both capillaries and nerve networks.
3. Odontoblastic layer; outermost layer which
contains odontoblasts and lies next to the
predentin and mature dentin
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The cementum
• Relatively soft bony tissue that covers the root
surface. Meets the enamel in a line surrounding
the tooth called the cement-enamel junction
(abbreviated as CEJ). Attached to the
periodontal ligament to be attached to the
bony socket of the alveolar bone supporting
the tooth.
• When exposed due to recession of the gum as in
old age, it is easily worn off.
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The supporting structures of a tooth:• Periodontal ligament
• Alveolar bone
• Gingiva
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The periodontal ligament
• Is a fibrous connective tissue made of regular bundle of
collagen fibers, which pass between the alveolar bone of the
tooth socket and the cementum.
• It therefore anchors the tooth within the socket but at the
same time allowing functional tooth movements to take place.
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The gingiva
• Is also known as a gum, it is a dense connective tissue
firmly attached to the underlining periosteum of the
alveolar bone and is lined by mucous membrane, which is
stratified
squamous
epithelium
with
patchy
keratinization
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The tongue
Is a mobile muscular structure that lies in the oral cavity
proper. It consists of intrinsic skeletal muscle covered with
mucous membrane.
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The tongue
• The tongue is made up of the body and the root; the body
forms the anterior two thirds of the tongue while the root
forms the posterior one third. The border between the two is
indentified by a V-shaped furrow known as the sulcus
terminalis.
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The posterior third of the tongue
• Mucous membrane of the posterior third of the tongue is
stratified squamous epithelium that shows patchy
keratinization
• The epithelium invaginates into the substance of the
tongue to form lingual tonsils. Beneath the lingual
tonsils are mucous glands that secrete into the bottom of
the tonsils
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The anterior part of the tongue
• This forms the body of the tongue; it is the most mobile
part of the tongue. Histologically it contains the intrinsic
and extrinsic muscles and the intrinsic muscles are
arranged in different directions.
• For the purpose of description the mucous membrane is
divided into dorsal and ventral surfaces.
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…anterior part of the tongue
• The mucous membrane of the ventral surface is
stratified keratinized epithelium and appears
smooth.
• The mucous membrane of the dorsal surface of the
anterior two thirds of the tongue is also stratified
squamous epithelium that is partially keratinized
in some places but contain numerous mucosal
projections known as lingual papillae. Because
of these mucosal projections the dorsal surface of
the tongue appears rough. However it is not
associated with lingual tonsils.
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The lingual papillae
• There are four types
of lingual papilla,
these are
1. filiform papilla,
2. fungiform papilla,
3. folliate papilla and
4. circumvalate papilla
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1. Filiform papillae
• These are most widely and uniformly distributed
over the whole of the anterior two thirds of the
dorsum of the tongue and are conical in shape
• The epithelium that forms the filiform papillae is
keratinized and do not contain the taste buds
• By providing the tongue with a rough surface they
aid in the manipulation and processing of
foods.
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Fillform Papilla
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2. Fungiform papillae
• These are fewer in number and are found in large
concentration on the sides and at the tip of the
tongue
• They are shaped like mushroom (hence the
fungiform) with a short stalk and broader cup.
• Their connective tissue core is richly vascularised &
the epithelium is stratified squamous epithelium
non-keratinized type
• The epithelium at the tip of the papilla contain smaller
number of taste buds and hence play an important
role in appreciation of taste
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3. Foliate papilla
• These are not well developed in humans and may be absent
in aged individuals.
• If present, they form lamellae along the posterior and
lateral border of the tongue.
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4. Circumvallate papillae
• These are the largest and least numerous papillae - in
humans there are between 8 and 15 of them. They are
located along the V-shaped depression, the sulcus
terminalis. Taste buds are particularly numerous on the
lateral surfaces of these papillae.
• They are associated with serous glands (von Ebner
glands) whose ducts open into the trenches surrounding
the papillae and the furrow of the sulcus terminalis.
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Taste Buds
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Taste Buds
• Taste buds are end organs for taste sensations. They are
barrel shaped and extend throughout the whole thickness of
the epithelium to open to the surface through a minute
gustatory pore. They are composed of three types of cells; the
gustatory cells, sustentacular cells and basal cells.
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Pharynx
• The pharynx is divided into three parts; the
Nasopharyx, Oropharynx, Laryngopharynx).
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Pharynx…
• The pharynx has three coats, an outer fibrous, middle
muscular and inner mucous membrane. The epitheliums is
stratified squamous non-keratinized type
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…oropharynx
• In the oropharynx two types of tonsils: the lingual tonsil
is located in the lamina propria in the posterior third or
pharyngeal part of the tongue. The palatine tonsils are pair
of tonsils on the lateral wall of the oropharynx between to
arches, the palatoglossal and palatopharyngeal muscles
respectively.
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…oropharynx
• The palatine tonsils are commonly inflamed resulting to a
clinical condition known as tonsillitis.
• These and two others, one single and paired in the
nasopharynx together forms Waldeyer’s ring of lymphoid
tissues around the entry into the respiratory and
gastrointestinal tracts.
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Nasopharynx
• The pharyngeal tonsils found in the posterior wall of the
nasopharynx when inflamed bring about the clinical
condition known as adenoids, which is more common in
children.
• A pair of tonsil found on the lateral wall of the nasal pharynx
close to the tubal elevation is known as tubal tonsils.
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GASTROINTESTINAL
TRACT
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The tubular part of the digestive
• The tubular part of the digestive system consists of
esophagus, stomach, small intestine, and large intestine.
• The GIT has a common general plan of organization and
possesses four layers that are known as tunics.
– Tunica Mucosa (Lining epithelium, lamina
propria, muscularis mucosa)
– Tunica submucosa (In some part contains
submucosal glands)
– Tunica Muscularis (Muscularis externa)
– Tunica Adventitia/Serosa
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The digestive
• Lining epithelium Varies from region to
region
– Oesophagus & lower part of anal canal –
Stratified squamous non-keratinized
– Stomach – Simple columnar secretory in
function
– Small
intestine
–
Simple
columnar
absorptive, secretory, goblet cells present
– Large intestine – simple columnar, absorptive,
secretory, goblet cells present in large
numbers
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…tunica Mucosa
• Lamina propria
– The lamina propria is a constituent of the
moist linings known as mucous membranes or
mucosa, which line various tubes in the body
(such
as
the
respiratory
tract,
the
gastrointestinal tract, and the urogenital tract.
– Lamina propria is considered to be a loose
connective tissue type. The cellular elements
comprise mainly of fibroblasts, plasma cells
and lymphocytes organized to form diffused
or aggregated lymphatic nodules.
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…tunica Mucosa
• Muscularis mucosa
– Is the third layer of tunica mucosa that
borders the tunica submucosa. It contains
two layer of smooth muscle fibers that are
organized into outer longitudinal and
inner circular layers.
– Function of muscularis mucosa may be
support and in contraction enhances
mixing the contents of the gastrointestinal
tract
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Tunica submucosa
• Is a layer of loose connective tissue that is found
between the mucosal layer and muscularis layer. It
is made up of large number of elastic fibers
particularly in the upper part of the GIT.
• It contains large blood vessels, lymphatic
vessels and parasympathetic plexus of nerves
called submucosal plexus or meissner’s plexus.
• The tunica submucosa contains mucus secreting
glands; the submucosal glands in the duodenum
and esophagus.
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Tunica Muscularis
• Tunica muscularis is also known as muscularis
externa. This layer consists of smooth muscle fibers
arranged in a thinner outer longitudinal and a
thicker inner circular layer
• In between the two layers there is another autonomic
nerve plexus, known as the myenteric or
Auerbach’s plexus. The plexus contains the
preganglionic fibers and ganglion cells of the
parasympathetic (enhance the tone of smooth
muscles & peristaltic), and postganglionic fibers of
the sympathetic (inhibits the tone of smooth
muscles & peristalsis)
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…tunica Muscularis
• In some parts of GIT the circular muscle later
becomes thick to form sphincters that regulates
passage of food materials e.g.
– pyloric sphincter between the duodenum and
the stomach and
– internal anal sphincter of the anal canal
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Tunica adeventitia/serosa
• This is the outermost layer. It is made up of
loose connective tissue composed of collagen
fibers.
• Tunica serosa is made up of a single layer of
flattened simple squamous methothelium.
• intraperitoneal organs are covered in serosa
(a layer of mesothelium, the visceral
peritoneum)
• retroperitoneal organs are covered in
adventitia (loose connective tissue)
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Histology of individual parts
of GIT
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Oesophagus
• It is a tube about 25cm long extending
from the pharynx to the stomach.
• Lining epithelium (tunica mucosa)
– Thick Stratified squamous non-keratinized
– The lower end of oesophagus, the epithelium
undergoes an abrupt transition to simple
columnar epithelium.
– The lamina propria contains mucosal
glands that secrete mucus.
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…oesophagus
• Tunica submucosa
– Contains any elastic fibers, which permit
distention during swallowing
– In the submucosa are groups of small mucussecreting glands, the esophageal glands.
They are more abundant in the upper part of
the oesophagus. Their ducts pass through the
tunica mucosa to open into the lumen.
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…oesophagus
• Tunica muscularis
– Contains circular inner layer and outer bundles
of longitudinal fibers.
– In the upper one third of the oesophagus the
muscles fibers are skeletal, their presence
allows the person to initiate swallowing
voluntarily
– The middle third contain a mixed skeletal
and smooth muscle fibers
– The lower third has smooth muscle fibers
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…oesophagus
• Tunica adventitia
– Is made up of loose connective tissue
containing longitudinally directed blood
vessels, lymphatic vessels and nerves.
– Above the stomach it contains elastic fibers
that attach the oesophagus to the diaphragm
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The
stomach
• It is a sac like dilatation of the alimentary tract that
lies between the oesophagus and the duodenum.
It receive the food from the oesophagus; the food is
compressed, churned and mixed with gastric
secretions to form chyme.
• Anatomically the stomach can be divided into
cardiac portion, fundus, the body and pyrolic
antrum.
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…the stomach
(histological features)
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…the stomach
(histological features)
• The stomach wall contains the usual four layers of
the digestive system
• The tunica mucosa
– Is thrown into longitudinal folds (rugae) which disappear
when the stomach is distended with food
– The surface epithelium contain numerous openings
called gastric pits that deriver secretions to the surface
– It consist of Simple columnar epithelia secretory in
function
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…the stomach
(histological features)
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The muscularis mucosa
It consists of the inner
circular and
longitudinal layers of
smooth muscles
The function may be
to support and aid
emptying of gastric
glands
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…the stomach
(histological features)
• The lamina propria
– It lies between the bottom of the pits and the muscularis
mucosa. It contains long gastric glands that are
closely packed and elements of connective tissue.
– The gastric glands are made up of cells, which secrete
mucus, HCl, pepsin and hormones such as gastrin
and cck
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…the stomach
(histological features)
• Gastric glands
Chief (zymogenic) cells.
–
Predominantly located in the body/base of
the gland. Secretes pepsinogen.
•
Parietal (oxyntic) cells
–
–
Larger than chief cells. Concentrated in
the central half of the gland.
Secretes hydrochloric acid and gastric
intrinsic factor
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…the stomach
(histological features)
• Tunica submucosa
– It consists of irregular connective tissue with
dense arrangement of collagen fibers
– The tunica submucosa of the stomach does
not have glands and participate in forming
rugae
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…the stomach
(histological features)
• Tunica muscularis
–
–
–
It is composed of three layers an inner oblique,
middle circular and an outer longitudinal layer.
The inner oblique muscle layer is most numerous near
the cardiac region, scanty over major part of the body
and probably absent at the pyloric portion.
The middle layer is thickest and equally distributed
throughout with more reinforcement at the pyloric
sphincter.
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Small intestine
• It measures approximately 6.25m and it consists of
duodenum 0.25m, jejunum 2.4m, and ileum 3.6m
• Although these three parts have certain distinctive
features, the pattern of organization is the same
and consists of the same four coats as already
described
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Duodenum
• It possesses following layers
• Mucosa:
–
–
It is comprised of surface epithelium, lamina propria
(containing glands) and muscularis mucosa.
It is lined with simple columnar epithelium which is
comprised of: (1) surface absorptive columnar cells;
(2) goblet cells and; (3) M cells.
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…duodenum
• Lamina propria:
– It consists of loose connective tissue with
infiltrated lymphocytes in the form of solitary,
nodules (unlike Peyers patches of ileum); but
in some places the lymphatic nodules are
aggregated.
– It also contains intestinal glands.
Note: Muscularis Mucosa: it consists of inner
circular and outer longitudinal layers of smooth
muscles.
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Intestinal gland
• In histology, an intestinal gland (also crypt of
Lieberkühn and intestinal crypt) is a gland
found in the epithelial lining of the small intestine
and colon. The glands and intestinal villi are
covered by epithelium which contains multiple
types of cells: enterocytes (absorbing water and
electrolytes), goblet cells (secreting mucus),
enteroendocrine cells (secreting hormones), tuft
cells and, at the base of the gland, Paneth cells
(secreting anti-microbial peptides) and stem
cells.
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…duodenum
• Tunica submucosa
– In the duodenum it contains branched tubular
glands known as Brunner’s glands, they are
Identification features of duodenum, lined by
mucous secreting columnar cells. Their ducts
open into the crypts of Lieberkuhn or directly
into the lumen
– The Brunner’s glands secrete alkaline mucus
that contains glycoproteins and bicarbonate
that help to neutralize the acids produced by the
stomach.
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Brunner’s Glands
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…duodenum
• Muscularls Externa:
• Beneath the mass of submucosal glands
smooth muscle (muscularis externa) consists
of an inner circular layer and an outer
longitudinal layer as In the rest of the small
intestine. The muscle layers are separated by
connective tissue containing myenteric
(Auerbach's) plexus.
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Jejunum
• Unique features
– This is very similar to the duodenum except
Brunner’s glands are absent. Mucosa consists
of simple columnar epithelium with goblet
– Extensive villi are present as are the crypts of
crypts of Lieberkuhn.
– The pilcae cicularis are permanent folds in the
intestinal mucosa.
– There are 2 layers of smooth muscle:
longitudinal and circular.
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Ileum
• Tunica mucosa
– The epithelium that forms the innermost part of
the mucosa has five distinct types of cells that
serve different purposes, these are: enterocytes
with microvilli, which digest and absorb nutrients;
goblet cells, which secrete mucin, a substance
that lubricates the wall of the organ; Paneth cells,
most common in the terminal part of the ileum,
are only found at the bottom of the intestinal
glands and release antimicrobial substances
such as alpha defensins and lysozyme
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• Lamina propria
Ileum
– An underlying lamina propria composed of
loose connective tissue and containing
germinal centers and large aggregates of
lymphoid tissue called Peyer's patches, which
are a distinctive feature of the ileum
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Ileum…
• Submucosa
– A submucosa formed by dense irregular
connective tissue that carries the larger blood
vessels and a nervous component called
submucosal plexus, which is part of the enteric
nervous system
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Ileum…
• External muscular layer
– An external muscular layer formed by two layers
of smooth muscle arranged in circular bundles in
the inner layer and in longitudinal bundles in the
outer layer. Between the two layers is the
myenteric plexus, formed by nervous tissue and
also a part of the enteric nervous system. A
serosa composed of mesothelium, a single layer
of flat cells with varying quantities of underlying
connective and adipose tissue. This layer
represents the visceral peritoneum and is
continuous with the mesentery
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Large
intestine
• Is the terminal part of the digestive tract
and it consists of the caecum, vermiform
appendix, colon, rectum and anal canal.
The colon is divided into ascending,
transverse, descending, and sigmoid parts.
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Large intestine…
• The Lining epithelium
– The mucosa of the large intestine does not
have villi and the epithelium is lined by
simple columnar epithelium, absorptive,
secretory, goblet cells present in large
numbers
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…large intestine
• Lamina propria:
– The lamina propria contains intestinal
mucosal glands
– Some solitary lymphatic nodules are
present in the lamina propria
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…large intestine
• Tunica submucosa
– It has the same plan as in the other areas but
has no glands
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…large intestine
• Tunica muscularis
– In the colon the longitudinal layer is arranged
into three condensations, which are known as
taenia coli.
– The circular layer is continuous, but the outer
longitudinal muscle layer is aggregated in
the form of three bands, which are known as
taenia coli except in the apendix and anal
canal. Taenia coli are responsible for gathering
the wall of large intestines into sacculations.
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…large intestine
• Tunica serosa
– Is similar to small intestine, but contains short
serosa process containing fats tissue known as
appendices epiploicae
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Vermiform Appendix
• Is the narrower diverticulum of the of the
caecum arising 2.5cm below the
ileocaecal valve
• Tunica mucosa
– Lined mostly by mucous (goblet) cells
– Villi are missing
– Intestinal glands are few
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…Appendix
• Lamina Propria
– Extremely rich in Lymphoid tissues that are
aggregated to form lymphoid nodules
• Muscularis mucosa
– Is thin and it forms incomplete layer and is
missing in some areas.
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Rectum
• Is a dilated lower part of the GIT that lies
between the sigmoid colon and the anal
canal
• Tunica mucosa
– Is lined by simple columnar cells with much
more goblet cells than the rest of the large
intestine
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…rectum
• Characteristic features
– Has longer intestinal glands 0.7mm long
– Lymphoid tissue are less abundant
– Muscularis mucosa is thick, in the lower
rectum, the longitudinal layer appear to
shorter than the length of the rectum. This
causes the mucosa to bulge into the lumen as
transverse shelves called plicae transversae,
one on the left and two on the rigth, they help
to support the feaces.
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…rectum
• Characteristic features
– In the lower rectum, the inner circular layer
thickens to form internal anal sphincter
muscle.
– The external anal sphincter is composed
of skeletal muscle fibers surrounding the
anal canal.
– There are no taenia coli
– there are numerous goblet cells
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Ana canal
• Characteristic features
– Anal canal is Histologically divided into
proximal, middle, and distal one third. The
division is based on the characteristic feature
of the mucosa in these three part.
– The upper folds are called anal columns or
column of Morgagn.
– At the lower end near the anal orifice they
unite to form transverse folds called anal
folds. Pockets of valves above the anal
valves form the anal sinuses
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…ana canal
• Tunica mucosa
– The upper half is lined by columnar epithelium
and the lower half is lined by stratified nonkeratinized squamous epithelium. However, at
the cutaneous zone of anal canal (anus) the
epithelial become keratinized, and beneath it
are circumanal glands.
– Circumanal glands consists of a group of
sebaceous and apocrine sweat glands that are
situated in the skin surrounding the anal orifice
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…ana canal
• Tunica submucosa
– Contain mucous secreting glands, the ducts of
which open in anal crypts that are situated close to
the anal sinuses
– It is also rich in plexus of haemorrhoidal veins
• Tunica muscularis
– The inner circular layer extends up to the upper one
third where it thickens to form the internal anal
sphincter.
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