ORAL MUCOUS MEMBRANE
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DEFINITION
• It is defined as a moist lining of oral cavity that
communicates with the exterior.
• Mucous membrane are also found lining other
body cavities such as sinuses, GIT, uterus etc.
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• The oral mucosa consists of two layers: an
epithelium (stratified squamous epithelium) &
an underlying layer of connective tissue, which
is the lamina propria.
• Beneath selected areas of the oral mucosa is a
loose connective tissue, the submucosa.
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CLASSIFICATION OF ORAL MUCOSA
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DEVELOPMENT & STRUCTURE OF
ORAL EPITHELIUM
• The cells vary from cuboidal or low columnar at
the connective tissue interface to flat squamous
at the surface.
• Most of the mucosal surface of the oral cavity is
lined by a nonkeratinized epithelium, except for
the gingiva, hard palate & dorsal surface of the
tongue where the epithelium is keratinized.
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•
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Four layers in nonkeratinized epithelium are:
The stratum basale,
The stratum spinosum,
The stratum intermedium,
The stratum superficiale.
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Four layers in keratinized epithelium are:
The stratum basale,
The stratum spinosum,
The stratum granulosum,
The stratum corneum.
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STRATUM BASALE
• Cells are cuboidal or low columnar.
• Cells form a single layer resting on the basal
lamina at the interface of the epithelium & lamina
propria.
• The epithelia of the oral mucosa are in a constant
state of renewal, & the basal cells show the most
mitotic activity.
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STRATUM SPINOSUM
• Is several cells thick.
• Mitotic figures can be occasionally seen.
• The stratum basale & first layers of the stratum
spinosum are referred to as the stratum
germinativum as this zone gives rise to new
epithelial cells.
• The cells are shaped like a polyhedron, with short
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cytoplasmic processes.
• Under the light microscope, the normal appearance
of these cells is accentuated by shrinkage artifacts
produced during routine fixation, staining &
mounting. Due to this, its known as prickle cell layer.
• Abundance of intracytoplasmic fibrils (tonofibrils)
that project toward & attach to the desmosomes.
• Membrane coating granules fuse with the
cytoplasmic membrane of the cell & exteriorize their
contents into the intercellular spaces.
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STRATUM GRANULOSUM
• The cells are flat & stacked in a layer three to five
cells thick.
• Consists of dense, relatively large (0.5 to 1 um)
keratohyaline granules in their cytoplasm.
• These are closely associated with ribosomes.
• Help to form the matrix for the numerous keratin
fibers found in the superficial layers.
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STRATUM CORNEUM
• The cells are very flat, devoid of nuclei, & full of
keratin filaments surrounded by a matrix.
• There is abrupt change between the stratum
corneum & stratum granulosum.
• These surface cells are continually being
sloughed & are replaced by the continual
migration of cells from the underlying layers.
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ULTRASTRUCTURE OF STRATUM
CORNEUM
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SCANNING ELECTRON MICROGRAPH
SURFACE VIEW OF EPITHELIAL CELLS.
OF
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TURNOVER OF ORAL EPITHELIUM
• High rate of turnover.
• Difficult to appreciate on a static diagram or
histologic slide.
• The dynamic nature of this epithelium is best
appreciated when cells are labeled experimentally
with radioactive thymidine, which tags DNA at
synthesis.
• The technique used to view the labeled DNA is
termed radioautography.
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TURNOVER
OF
EPITHELIAL
CELLS
REVEALED BY 3H THYMIDINE LABELING.
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• Sulcular epithelium takes 10 days to
renew, whereas the general oral mucosa
takes approximately 12 to 13 days.
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NONKERATINIZED EPITHELIUM
• The surface cells retain their nuclei.
• The cytoplasm does not contain keratin
filaments.
• The stratum corneum & granulosum is
absent.
• E.g. lining mucosa.
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PARAKERATINIZED EPITHELIUM
• The surface cells have dark staining pyknotic
nuclei.
• The cytoplasm contains little if any keratin
filaments.
• E.g. gingiva.
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ILLUSTRATION OF THREE FUNCTIONAL TYPES OF
ORAL EPITHELIUM.
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JUNCTION
OF
EPITHELIUM
CONNECTIVE TISSUE
&
• Connective tissue, with its inductive properties,
exerts control over the overlying epithelium.
• The basement membrane is composed of three
parts:- Lamina lucida, which is less dense & is toward the
epithelial side;
- Lamina densa, middle of the three parts;
- Lamina reticularis, which is less dense than the
lamina densa & is located next to the lamina
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propria.
• Type IV collagen & laminin, a glycoprotein, are
major components of the lamina densa.
• Basal cells of the epithelium are not attached to the
connective tissue proper, but rather form
mechanical adhesions with the basal lamina. These
attachments are hemidesmosomes.
• Fine collagen fibers attach to lamina on the
connective tissue side. These fibers are anchoring
fibers, composed of type VII collagen.
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DIAGRAM OF HEMIDESMOSOMES
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LAMINA PROPRIA
• Is the connective tissue layer immediately below the
epithelium.
• Can be divided into the papillary layer & reticular
layer.
• In the papillary layer, finger-like projections of
connective tissue extend into the deep surface of the
epithelium.
• An increase in the number & length of the papillae
is seen in areas where mechanical adhesion between
the epithelium & lamina propria is required
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(masticatory mucosa).
• In areas of lining mucosa, the reticular or
subpapillary layer predominates.
• The blood supply consists of a deep plexus of large
vessels in the submucosa, which gives rise to a
secondary plexus in the papillary layer of the lamina
propria.
• Capillary loops extend into the connective tissue
papillae.
• The epithelium is avascular; therefore, its metabolic
needs must come via the vessels of the lamina
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propria.
THE LAMINA PROPRIA CONSISTS OF THE PAPILLARY
LAYER & RETICULAR LAYER, BELOW WHICH IS
SUBMUCOSA.
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SUBMUCOSA
• In most areas of the mouth, the submucosa is
absent or limited.
• Serves primarily as an attachment for the lamina
propria to the underlying bone or skeletal muscle.
• Found in the cheeks, lips, & parts of palate, & is a
less dense component than the lamina propria.
• Its functions are nutrition & defense.
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• It is the site containing adipose tissue & minor
salivary glands in the oral cavity.
• In the bony areas with no submucosa, fibers of
the lamina propria attach tightly to bone.
• The mucosa & lamina propria in these areas is
generally referred to as mucoperiosteum.
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FULL THICKNESS OF CHEEK
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CROSS SECTION OF TONGUE
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LINING MUCOSA
• Is smooth & shiny.
• Oral epithelium is less pigmented than the
epithelium of the skin & varies in color from light
pink to darker pink or red.
• The hues are influenced by the underlying
capillary network in relation to the free surface
& by the amount of melanin pigment in the
epithelial cells.
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LINING MUCOSA OF FLOOR OF
MOUTH
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LIP WITH SKIN ON OUTER SURFACE & LINING
MUCOSA ON INNER SURFACE.
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VERMILION BORDER
• It is the junction between the skin & mucous
membrane.
• The epithelium is thin.
• A protein eleidin is present, which is more
transparent than the protein keratin.
• Ectopic sebaceous glands are seen in the vermillion
border at the corners of the mouth or more laterally
in the cheeks opposite the molar teeth. These are
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called fordyce’s spots.
VERMILLION BORDER WITH ITS
COVERING OF CLEAR ELEIDIN.
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SOFT PALATE
• Is covered by lining mucosa, which is more
pink than the hard palate.
• A layer of elastic fibers separates the lamina
propria from the underlying submucosa.
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MUSCLE IN SUBMUCOSA OF VENTRAL
SURFACE OF TONGUE.
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HARD PALATE
• In the anterior lateral regions of the hard palate, the
submucosa contains fatty tissue.
• The lateral regions of the posterior parts contain the
palatine glands, which extend posteriorly into the
soft palate.
• These glands are pure mucous glands containing
only mucous acini.
• The median raphae has no submucosa & there is
only dense fibrous attachment to the underlying
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DIAGRAM OF REGIONS OF PALATE.
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• In the lateral regions of the palatine mucosa,
both fatty & glandular tissue make up the
submucosa.
• Rugae do not cross the midline but are easily
seen & palpated, & can be felt with the tongue.
• The connective tissue fibers pass directly from
the papillary layer of the lamina propria into the
underlying bone. These are termed traction
bands & make the rugae immovable structures.
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• In the lateral region of the palate near the
maxillary molar tooth, there is no submucosal
layer adjacent to the teeth overlying the
alveolar bone, &
• The fibers of the lamina propria of the palate
& gingiva are continuous.
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DIAGRAM OF TONGUE, WITH
SPECIALIZED MUCOSA SHOWN ON
DORSUM OF TONGUE
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INTRA-EPITHELIAL NON-KERATINOCYTES
• These are known as clear cells because they
have a clear halo around their nuclei.
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These cells comprise four different types:
Langerhans’ cells
Merkel cells
Melanocytes
Lymphocytes.
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LANGERHANS’ CELLS
• Are found in the stratum spinosum &, occasionally in
stratum basale.
• These cells have long, thin extensions of the
cytoplasmic membrane, called dendrites.
• They can be distinguished from keratinocytes by the
absence of desmosomes & tonofilaments.
• Can be distinguished from the melanocytes by the
absence of premelanosomes.
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• Contains the rod shaped or racquet shaped birbeck’s
granules, which allows for positive identification at
the ultrastructural level.
• Are antigen presenting cells.
• They engulf antigens from the external environment
& the intracellular lysosomes split the antigens into
peptide components. These fragments are then
transferred to T-lymphocytes.
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MERKEL CELLS
• Are situated in the basal layer of the gingival
epithelium.
• Possess occasional desmosomes & tonofilaments.
• Are usually associated with an axon terminal.
• The merkel cell & associated axon terminal form a
complex that serves as a touch receptor.
• Are usually found in groups or clusters.
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MELANOCYTES
• Are melanin producing cells located in the basal
layer of the gingival epithelium.
• These cells arise from the neural crest.
• Lack tonofibrils, desmosomes & hemidesmosomes.
• Are highly dendritic in nature.
• The most characteristic feature of the melanocyte is
the melanosome granule found within the
cytoplasm.
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• A more heavily pigmented gingiva is due to
the production of melanin & its subsequent
uptake by the epithelial cells.
• There is a great variability in the location &
distribution of melanin in the oral cavity.
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CLINICAL CONSIDERATIONS
• The oral mucosa can change according to various
factors, including smoking, age & disease.
• Over 7% of the total number of cancers
diagnosed in the United States are located in the
oral & oropharyngeal areas.
• The process of keratinization can be altered in
cancerous & precancerous lesions such as
leukoplakia.
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• Thinning of the epithelium occurs in relation to
prosthetic devices covering the surface of the
mucosa.
• Changes in salivary flow- due to age, radiation or
disease- disrupt the normal maturation &
differentiation of the epithelial cell layers.
• The healing capacity of the oral mucosa is greater
than that of the skin. Orthognathic surgery to move
segments of the mandible & maxilla can be
performed using an intraoral approach to take
advantage of these characteristics.
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