The Anatomy and Histology of the Digestive System

DIGESTIVE SYSTEM-1
DR.DEEPAK N.KHEDEKAR
DEPARTMENT OF ANATOMY
NOV 2016
1Dr.Deepak N.Khedekar/LTMMC/NOV/2016

LIP

LIP
• Entry point of the
alimentary canal.
• Thin keratinized
epithelium of face
skin changes to
the thick
parakeratinized
epithelium of the
oral mucosa.

• Skin of the face(Top),
the red margin of the
lip(middle), and the
transition to the oral
mucosa (lower).
• Change in thickness of
the epithelium from
the facial portion of
the lip to the interior
surface of the oral
cavity 4Dr.Deepak N.Khedekar/LTMMC/NOV/2016

KERATINIZED EPITHELIUM-Lip (TOP)
H&E ( ×120 )
• Keratinized
epithelium (EP) of
the face
• Dermis -Hair follicles
(HF) , sebaceous
glands and arrector
pili muscle(Thin
skin) BV- venous blood vessels, EP-epithelium,HF-hair
follicle ,M- melanin pigment ,SG-stratum
granulosum ,SGl- sebaceous gland arrowheads,
connective tissue papillae ,

KERATINIZED EPITHELIUM - LIP (TOP)
H&E ( ×380 )
• Reddish brown material in
the basal cells- pigment
melanin (M)
• Dark blue near the
surface- stratum
granulosum (SG) with its
deep-blue-stained
keratohyalin granules.

RED MARGIN
H &E × 120

RED MARGIN
H &E × 120
• Keratinized Epithelium of the LIP is much
thicker than that of the face.
• Stratum granulosum is present
• Coloration of the red margin is due the deep
penetration of the CT papillae into the
epithelium (arrowheads).
• Extensive vascularity of the underlying CT ,
(BV), allows the color of the blood

RED MARGIN
H &E × 380
• Sensitivity of the
red margin to
stimuli such as light
touch is due to the
presence of an
increased number
of sensory
receptors.
• Meissner’s
corpuscle, (MC)
seen in each of the
two deep papillae in

MUCOCUTANEOUS JUNCTION, H&E × 120
• Transition from the keratinized red margin to the
fairly thick stratified squamous parakeratinized
epithelium of the oral mucosa.
• Stratum granulosum suddenly ends.

MUCOCUTANEOUS JUNCTION, H&E × 380
• Beyond the site where
the stratum granulosum
cells disappear, nuclei are
seen in the superficial
cells up to the
surface(arrows).
• The epithelium is also
much thicker at this point
• and remains so
throughout the oral
cavity.

DEEPER STRUCTURES OF LIP
• Labial glands –tubuloacinar, mucus secreting
in deep CT
• Adipose cells
• Central core is formed by Skeletal muscle-
orbicularis oris

LIP

TOOTH

TOOTH
• Major component of the oral cavity
• Essential for the the digestive process.
• Embedded in and attached to the alveolar
processes of the maxilla and mandible.
(Gomphosis)
• Children have 10 deciduous (primary, milk)
teeth in each jaw, on each side:
• Adult has 32 Permanent (secondary) teeth

TOOTH -HISTOLOGY3 specialized tissues:
Enamel,
Dentin,
Cementum
Parts of the tooth :
Crown - Ends at the
neck, or cervix, of
the tooth at the
cementoenamel jn.
Root -covered by
cementum, a
bonelike material.

Enamel
• Hard, thin ,translucent layer of acellular
mineralized tissue
• Covers the crown of the tooth.
Dentin
• Most abundant dental tissue
• Lies deep to the enamel in the crown and
cementum
• Unique tubular structure and
biochemical composition support the
more rigid enamel and cementum

CEMENTUM
• Thin, pale-yellowish ,bone like calcified tissue
• Covering the dentin of the root of the teeth.
• Softer and more permeable than dentin.
• Easily removed by abrasion when the root
surface is exposed to the oral environment.

ENAMEL
• Hardest substance in the body;
• Consists of 96 to 98% calcium hydroxyapatite.
• An acellular mineralized tissue.
• Varies in thickness over the crown and may be
as thick as 2.5 mm on the cusps (biting and
grinding surfaces) of some teeth.
• Once formed it cannot be replaced.
• Unique tissue because, as it is a highly
mineralized material derived from epithelium.

ENAMEL
• Clinical crown-Enamel
that is exposed and
visible above the gum
line
• Aanatomic crown- all
of the tooth that is
covered by enamel,
some of which is
below the gum line.

ENAMEL
Enamel rods-
• Span the entire thickness of the enamel layer.
• Thin structure extending from the Dentino-
Enamel junction to the surface of the enamel.
• Where the enamel is thickest, at the tip of the
crown, the rods are longest
• Embryology: Produced by ameloblasts

ENAMEL RODS • Rods reveal a keyhole
shape.
• Head- upper ballooned
part of the rod, oriented
superiorly,
• Tail- lower part of the rod,
is directed inferiorly.
• Within the head, the
enamel crystals are
oriented parallel to the
long axis of each rod.
• Within the tail, the crystals
are oriented more
obliquely.

ENAMEL RODS

DENTIN
• Dentin is produced by neural crest–derived
odontoblasts of the adjacent mesenchyme.
• Calcified material that forms most of the tooth
substance.
• Lies deep to the enamel and cementum.

DENTIN
• Contains less hydroxyapatite than enamel,
about 70%, but more than is found in bone
and cementum.
• Like ameloblasts, odontoblasts are columnar
cells that contain a well-developed rER, a large
Golgi apparatus, and other organelles
associated with the synthesis and secretion of
large amounts of protein
Dr.Deepak N.Khedekar/LTMMC/NOV/2016 26

DENTINAL TUBULES
• Apical surface of the odontoblast is in contact
with the forming dentin
• Junctional complexes of the odontoblasts
separate the dentine from the pulp
• Odontoblast processes embedded in the dentin
in narrow channels called dentinal tubules .
• Tubules and processes continue to elongate as
the dentin continues to thicken by rhythmic
growth.

DENTIN -GROWTH LINES
• Also known as Incremental lines of von
Ebner OR thicker lines of Owen
• Produces by Rhythmic growth of dentin
produces certain “growth lines” in the dentin
• Mark significant developmental times such as
birth (neonatal line)
• Study of growth lines has proved useful in
forensic medicine.

CEMENTUM
• Avascular structure ,covers the root of the tooth.
• Thin layer of bonelike material
• Secreted by cementocytes , cells that closely
resemble osteocytes.
• Like bone, cementum is 65% mineral.
• Contain Lacunae and canaliculi consist of in the
the cementocytes and their processes,

CEMENTUM
• Consist of canaliculi which do not form an
interconnecting network.
• A layer of cementoblasts is seen on the outer
surface of the cementum, adjacent to the
periodontal ligament.
• Sharpey’s fibers -Collagen fibers that project
out of the matrix and embed in the bony matrix
of the socket wall form the bulk of the
periodontal ligament

CEMENTUM
• Elastic fibers are also a component of the
periodontal ligament allowing slight
movement of the tooth to occur naturally.
• Forms the basis of various orthodontic
procedures
• During corrective tooth movements, the
alveolar bone of the socket is resorbed and
resynthesized, but the cementum is not.

SHARPEYS FIBRES

DENTAL PULP AND CENTRAL PULP CAVITY
(PULP CHAMBER)
• Connective tissue compartment bounded by
the tooth dentin.
• Space within a tooth
• Occupied by dental pulp, a loose connective
tissue that is richly vascularized and supplied
by abundant nerves
• Takes the general shape of the tooth

CENTRAL PULP CAVITY
• Apical foramen- Vessels and nerves enter the
pulp cavity at the tip (apex) of the root
• Blood vessels and nerves extend to the crown of
the tooth, where they form vascular and neural
networks beneath and within the layer of
odontoblasts.
• Because dentin continues to be secreted
throughout life, the pulp cavity decreases in
volume with age.

PULP CAVITY

SUPPORTING TISSUES OF THE TEETH
include…
• Alveolar bone
• Alveolar processes
of the maxilla and
mandible
• Periodontal
Ligaments
• Gingiva.

PERIODONTAL LIGAMENT
• Fibrous connective tissue
• Joining the tooth to its surrounding bone.
• Provides for the following :
 Tooth attachment (fixation)
 Tooth support
 Bone remodeling (during movement of a
tooth)

DRIED SECTION OF TOOTH
Shows following features…
• Lines of schreger
• Lines of Retzius
• Interglobular spaces
• Granular layers of Tomes

TONGUE
• Muscular organ projecting into the oral cavity.
• Covered with a mucous membrane that
• Consists of stratified squamous epithelium,
keratinized in parts
• Resting on a loose connective tissue.
• Parts : Root &Free part i.e body
• Surfaces: Dorsal & Ventral

TONGUE- MUCOSA
• Dorsal surface
Mucosa is modified
to form three types
of papillae:
filiform,
fungiform, and
circumvallate

TONGUE - PAPILLA
• Circumvallate papillae form a V-shaped row
that divides the tongue into a body and a root
• Dorsal surface i.e. the portion anterior to the
circumvallate papillae, contains filiform and
fungiform papillae.
• Parallel ridges bearing taste buds are found on
the sides of the tongue and are particularly
evident in infants.

MUSCLES OF THE TONGUE
• Contains both intrinsic and extrinsic voluntary
striated muscle.
• Arranged in three interweaving planes, with
each arrayed at right angles to the other two.
• Arrangement is unique.
• Provides enormous flexibility and precision in
the movements ,essential to human speech as
well as to its role in digestion and swallowing.
• Arrangement also allows easy identification.

TONGUE
Dorsal surface,
H&E ×65; inset ×130

TONGUE, DORSAL SURFACE
H&E.
Filiform papillae (Fil P)-
• Most numerous of the
three types of papillae.
• Conical projections of
the epithelium, with the
point of the projection
directed posteriorly.
• Do not possess taste
buds
• Composed of stratified
squamous keratinized E

TONGUE-DORSAL SURFACE, H&E
Fungiform papillae-
• Isolated, slightly rounded, elevated structures
situated among the filiform papillae.
• Large CT core (primary CT papilla) forms the center
of the fungiform papilla, and smaller CT papillae
(secondary CT papillae) project into the base of the
surface epithelium
• CT of the papillae is highly vascularized.
• Deep penetration of CT into the epithelium,
combined with a very thin keratinized surface, the
fungiform papillae appear as small red dots

FUNGIFORM PAPILLA

TONGUE-VENTRAL
SURFACE, H&E ×65.
• Smooth surface of the
stratified squamous E.
(Ep)
• Epithelial surface
usually not keratinized.
• CT is deep to the
epithelium;
• Deeper still is the
striated muscle (M).

TONGUE-VENTRAL
SURFACE, H&E ×65.
• CT papillae, project into
the base of the epithelium
of both surfaces give the
epithelial– CT junction an
irregular profile.
• CT papillae are cut
obliquely
• Appear as small islands of
CT within the epithelial
layer

TONGUE-VENTRAL SURFACE,
H&E ×65
• Muscle (M)- is striated
,fibers travel in three
planes.
• Nerves (N) observed in the
CT septa between the
muscle bundles.
• Surface of the tongue
behind the vallate papillae
(the root of the tongue)
contains lingual tonsils

PAPILLAE AND ASSOCIATED TASTE BUDS
• Foliate, fungiform, and circumvallate,
contain taste buds(Tb) in their epithelium.
Fungiform papillae-
• Most numerous near the tip of the tongue.
• Tb are present in the epithelium on their
dorsal surface.

TASTE BUDS
• Ducts of lingual salivary glands (von Ebner’s
glands) empty their serous secretions into the
moat surrounding each circumvallate papilla.
• Secretions flush material from the moat to allow
the taste buds to respond to new stimuli.
• Taste buds in section appear as oval, pale-
staining bodies that extend through the thickness
of the epithelium. A small opening at the
epithelial surface is called the taste pore.

TASTE BUDS
• Tb in the epithelium covering the circumvallate
and foliate papillae are located in deep clefts

• C- cleft CTP, connective tissue papillae D, ducts Ep, epithelium lining
the clefts LCT, loose connective tissue LSG, lingual serous glands SE,
stratified nonkeratinized epithelium ,TP, taste pore

TASTE BUDS
• Oval, pale-staining
structures that extend
through much of the
thickness of the
epithelium.
• BC- Basal cells
• NF- nerve fibers
• NSC- neuroepithelial
sensory cells
• SC- supporting cells
• TP- taste pore

TASTE BUDS
• React to only five stimuli: sweet, salty, bitter,
sour, and umami.
• Modalities appear to be more concentrated…
@ the tip of the tongue- sweet stimuli,
@Posterolateral to the tip-salty stimuli,
Circumvallate papillae - bitter and umami
stimuli.

TASTE BUDS
Neuroepithelial sensory cells (NSC)-
• Cells with the large, round nuclei,most numerous
• Possess microvilli @ their apical surface
• Form a synapse with the afferent sensory fibers that
make up the underlying nerve.
Supporting cells (SC)-Contain microvilli on their apical
surface.
Basal cells (BC)- small cells present at base
• Stem cells for the supporting and neuroepithelial
cells which have a turnover life of about 10 days

• Portion of the
alimentary canal
that extends from…
• 1.Proximal part of
the esophagus TO
• 2.Distal part of the
anal canal
• Hollow tube of
varying diameter.
Tube has the Same
basic structural
organization
throughout its
length.

GIT
Wall is formed by four distinctive layers.
1.Mucosa- consisting of a
Lining epithelium,
Lamina propria- an underlying connective
tissue
Muscularis mucosae, composed of smooth
muscle
2.Submucosa- consisting of dense irregular CT
3.Muscularis externa- consisting in layers of
smooth muscle

BASIC LAYERS OF GIT
4.Serosa- a serous membrane consisting of a
simple squamous E., the mesothelium, and a
small amount of underlying connective tissue.
Adventitia consist of CT is found where the wall
of the tube is directly attached or fixed to
adjoining structures (i.e., body wall and
retroperitoneal organs).

ESOPHAGUS
low-magnification ,H&E

Mucosa
Epithelium- Nonkeratinized
stratified squamous
• Surface cells may exhibit
some keratohyalin
granules.
Lamina propria-
• Consist of diffuse lymphatic
tissue and lymphatic
nodules,
• Proximity to ducts of the
esophageal mucous glands

MUCOSA
Muscularis mucosae-
• Composed of
longitudinally organized
smooth muscle.
• Unusually thick in the
proximal portion.
Three principal functions of
mucosa:
Protection,
Absorption, and
Secretion

SUBMUCOSA
• Consists of dense
irregular CT
• Contains the larger
blood and lymphatic
vessels, nerve fibers and
ganglion cells.
• Nerve fibers and
ganglion cells make up
the submucosal plexus
(Meissner’s plexus).
• Submucosal Glands are
also present .

MUSCULARIS EXTERNA
• Consists of two muscle layers, an inner
circular layer and an outer longitudinal layer
• Differs from the muscularis externa found in
the rest of the digestive tract
• Upper one third - striated muscle, a
continuation of the muscle of the pharynx.
• Middle third -Striated muscle and smooth
muscle bundles are mixed and interwoven.
• Distal third- consists only of smooth muscle,
as in the rest of the digestive tract.

MUSCULARIS EXTERNA
• Nerve plx, the myenteric plx (Auerbach’s plx), is
present between the outer and inner muscle layers.
• Plx innervates the muscularis externa
Adventitia
• Esophagus is fixed to adjoining structures throughout.
• After entering the abdominal cavity, the short
remainder of the tube is covered by serosa, the
visceral peritoneum.
Mucosal and submucosal glands of the esophagus
secrete
mucus to lubricate and protect the luminal wall. 68Dr.Deepak N.Khedekar/LTMMC/NOV/2016

ESOPHAGUS

ESOPHAGEAL GLANDS PROPER
• Two types ,both secrete mucus,
Esophageal glands proper lie in the submucosa-
• Scattered along the length of the esophagus
• More concentrated in the upper half.
• Small, compound, tubuloalveolar glands
• Excretory duct is composed of stratified squamous
epithelium
• Mucus produces by it is slightly acidic and serves to
lubricate the luminal wall.

ESOPHAGEAL CARDIAC GLANDS
• Found in the lamina propria of the mucosa.
• Present in the terminal part of the esophagus, OR
in the beginning portion of the esophagus.
• Produce neutral mucus.
• Protect the esophagus from regurgitated gastric
contents. Under certain conditions, however,
they are not fully effective,and excessive reflux
results in pyrosis, a condition more commonly
known as heartburn. may progress to fully
developed (GERD).

MUSCLE OF THE ESOPHAGEAL WALL
• Innervated by both autonomic and somatic NS.
• Striated musculature in the upper is innervated
the vagus nerve, (from the nucleus ambiguus).
• Smooth muscle of the lower part is innervated by
visceral motor neurons of the vagus (from the
dorsal motor nucleus).
• Postsynaptic neurons are located in the wall of
the esophagus.

ESOPHAGUS-low-magnification ,H&E

THE END

The Anatomy and Histology of the Digestive System

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