Oral Mucosa in Health

8/10/2019 Oral Mucosa in Health

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KMCT DENTAL COLLEGEManassery, Mukkam

ORAL MUCOSA

IN HEALTH

Presented By:

Niyas Ummer

1stYear PG

Department of Oral Medicine and Radiology


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DefinitionMucus Membrane: Moist lining of gastrointestinal tract, nasal passages, and other body

cavities that communicate with the exterior. This lining of oral cavity is Oral Mucous

Membrane or Oral Mucosa.

Parts of Oral CavityThe oral cavity consists of two parts:

i.Vestibule (outer)

ii.Oral Cavity Proper (inner)

Boundaries Superiorlyhard & soft palates

Inferiorlyfloor of mouth and tongue

Posteriorlyfaucial pillars and tonsils

Anteriorlylips

Functions of Oral Mucosa

1. Protection:

Separates deeper tissues and organs from environment

Protect from mechanical forcesand surface abrasions

Adaptations to withstand insults

Barrier to microorganisms and their toxic products

2.

Sensation: Receptors for temperature, touch and pain

Taste buds of tongue

Reflexes are also initiated by receptors

3. Lubrication:

Saliva from salivary glands - maintains moist surface

Sebaceous glands - secrete sebum

4. Thermal Regulation:

Dissipation of body heat in some animals by panting

No such role in humans

Clinical FeaturesCharacteristic features:

Deeper colour

Moist surface

Absence of appendages

Only minor salivary glands, and occasional sebaceous glands (no sweat glands)

Smoother surface, fewer folds/wrinkles Variable firmness and thickness


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3. Stratum Granulosum

Cells are flat

Found in layers of three to five cells thick

Prominent in keratinized epithelium (absent in nonkeratinized)

Cells have keratohyaline granules in their cytoplasm - help to form the matrix

of the keratin fibres found in the superficial layer

4. Stratum Corneum

Cells are flat, devoid of nuclei and full of keratin filament surrounded by a

matrix

Cells are continuously being sloughed - replaced by epithelial cells that

migrate from the underlying layers

Parakeratinized Epithelium

Surface cells have dark staining pyknotic nuclei. The cytoplasm contains little if any

keratin filaments.

Nonkeratinized Oral Epithelium

Nonkeratinized epithelial cells in the superficial layers do not have keratin filaments

in the cytoplasm. The surface cells also have nuclei. The stratum corneum and stratum

granulosum layers are absent. This epithelium is associated with lining of the oral cavity.

Turnover of Oral Epithelium

High rate of turnover

Difficult to appreciate on a static diagram or histologic slide

Sulcular epithelium takes 10 days to renew

General oral mucosa takes approximately 12 to 13 days

Nonkeratinocytes

Cells that differ in appearance from other epithelial cells. They have a clear halo around

their nuclei. Such cells have been termed clear cells:

Melanocytes

Langerhan Cells

Merkel Cells

Inflammatory Cells

Melanocytes

Melanocytes

One factor affecting color of the oral mucosa is melanin pigmentation. Melanin is a

pigment produced by specialized cells called melanocytes. Situated in the basal layer of the

oral epithelium, they arise embryologicallyfrom the neural crest ectodermand enter the

epithelium at 11 weeks of gestation. They divide and maintain themselves (self-

reproducing). They possess long dendritic (branching) processes that extend between the

keratinocytes. Melanin is synthesized within the melanocytes as small structures called


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melanosomes.It is transferred into the cytoplasm of adjacent keratinocytes by the dendritic

processes of melanocytes. Groups of melanosomes are called melanin granules.

Lightly and darkly pigmented individuals have the same number of melanocytes in

any given region. Color differences result from:

Relative activity of the melanocytes in producing melanin

Rate at which melanosomes are broken down in the keratinocytes

Melanophagesare macrophages that have taken up melanosomes produced by

melanocytes in the epithelium. Melanin pigmentation seen most commonly clinically -

gingiva, buccal mucosa, hard palate, and tongue.

Langerhan Cells

They are dendritic cells seen above the basal layers of epithelium. Source is bone

marrow. They appear in the epithelium at the same time as, or just before, the melanocytes.They are capable of limited division within the epithelium. They move in and out of the

epithelium and can migrate from epithelium to regional lymph nodes.

Immunologic function - recognizing and processing antigenic material and presenting it to T

lymphocytes. They are characterized ultrastructurally by a small rod- or flask-shaped

granule, sometimes called the Birbeck granule.

Merkel Cells

They are situated in the basal layer of epithelium. They are not dendritic and does

possess keratin tonofilaments and occasional desmosomes. They arise from the

differentiation of an epidermal progenitor during embryonic development.

Merkel cells are sensory and respond to touch. Characteristic feature is presence of

small membrane-bound vesicles in the cytoplasm, situated adjacent to a nerve fiber

associated with the cell. Granules liberate a transmitter substance across the synapse-like

junction between the Merkel cell and the nerve fiber, which triggers an impulse.

Inflammatory Cells

Clinically normal areas of mucosa show a number of inflammatory cells in the

nucleated cell layers. Cells are transient and do not reproduce themselves.

Cells seen:

Lymphocytes (frequently)

Polymorphonuclear leukocytes

Mast cells

Lymphocytes often are associated with Langerhans cells, which are able to activate T

lymphocytes


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Keratinocytes produce cytokines that modulate function of Langerhans cells. Langerhans

cells produce cytokines (interleukin-1) which activate T lymphocytes and aid in responding

to antigenic challenge. Interleukin-1 also increases activity of melanocytes, which affects

pigmentation. Cytokines can also influence the activity of fibroblasts.

Junction of Epithelium and Lamina Propria

It is the region where connective tissue of the lamina propria meets the overlying

oral epithelium. It shows an undulating interface at which papillae of the connective tissue

interdigitate with epithelial ridges.

Significance:

1. Larger surface area of the interface for better attachment

2. Enable forces applied at the surface to be dispersed over a greater area of

connective tissue

3.

Metabolic exchange between the epithelium and connective tissue (epithelium hasno blood vessels)

4. Masticatory mucosa - greatest number of papillae per unit area

5. Lining mucosa - papillae are fewer and shorter

Basal Lamina

It cannot be visualized directly by light microscopy using conventional stains. In

histologic sections of oral mucosa stained by the periodic acidSchiff reaction, it appears as

a bright, structureless band at the interface between the epithelium and subjacentconnective tissue.

Basal lamina runs parallel to the basal cell membrane of the epithelial cells.

At the ultrastructural level, it consists of three zones:

Lamina Lucida - slightly thinner than the lamina densaappears as clear zone

Lamina Densa - homogeneous, finely fibrillar planar assembly of extracellular matrix

molecules

Lamina Fibroreticularis

Anchoring fibrils:They are made up of collagen type VII. They insert into the lamina densa, and form a

flexible attachment between the basal lamina and subjacent connective tissue.

Cells of Lamina Propria

The lamina propria contains several different cells: fibroblasts, macrophages, mast

cells, and inflammatory cells.


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Fibroblasts

They are the principal cells responsible for the elaboration and turnover of fiber and

ground substance, and maintains connective tissue integrity. Low rate of proliferation is

seen.

During wound healing, fibroblasts divide in the adjacent uninjured tissues and their

numbers increase. They can become contractile and actin content increases. This results in

wound contraction. In certain disease states, they may be activated and secrete more

ground substance.

Macrophages

Round, stellate or sometimes fusiform cells which are difficult to distinguish from

fibroblasts unless they hav phagocyted extracellular debris. They have smaller and denser

nuclei, with less rough endoplasmic reticulum. Cytoplasm contains lysosomes.

Functions:i. Phagocytosis- Ingest damaged tissue or foreign material and initiate breakdown

ii. Antigen presenting- Processing of ingested material and increasing its antigenicity

before presenting to cells of the lymphoid series

iii. Repair- Stimulation of fibroblast proliferation

Two special types of macrophages can be identified specifically:

Melanophage- in pigmented oral mucosa, cell has ingested melanin granules

extruded from melanocytes Siderophage- contains hemosiderin derived from extravasated red blood cells due

to mechanical injury

Mast Cells

Large spherical or elliptical mononuclear cell. Nucleus is small relative to cell size.

Large number of intensely staining granules that occupy its cytoplasm, which contain

histamineand heparin.

They play an important role in maintaining normal tissue stability and vascular homeostasis.

Inflammatory CellsLymphocyte and plasma cell are present in small numbers scattered throughout the lamina

propria. Following an injury, they are found in significant numbers, and release cytokines,

which influences the behavior of the overlying epithelium.

Type of inflammatory cell depends on the nature and duration of injury:

Acute conditions - polymorphonuclear leukocytes

Chronic conditions - lymphocytes, plasma cells, monocytes, and macrophages


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Fibres and Ground Substance

Intercellular matrix consists of two major types of fibers:

Collagen

Elastin

These fibres together with fibronectin are embedded in a ground substance.

Collagen

Collagen in the lamina propria is primarily type I and type III. Types IV and VII

occurring as part of the basal lamina. Type V may be present in inflamed tissue.

Elastic Fibers

When stained using specific methods, some elastic fibers can be seen in most

regions of the oral mucosa, but they are more abundant in the flexible lining mucosa, where

they function to restore tissue form after stretching. Unlike collagen fibers, elastic fibers

branch, anastomose, and run singly rather than in bundles.

Ground Substance

It appears amorphous by light and electron microscopy. It consists of heterogeneous

molecular complexes permeated by tissue fluid. Chemically, they are subdivided into two:

1. Proteoglycans- polypeptide core to which glycosaminoglycans (consisting of hexose

and hexuronic acid residues) are attached

E.g. hyaluronan, heparan sulfate, versican, decorin, biglycan, and syndecan

2. Glycoproteins- polypeptide chain to which only a few simple hexoses are attached

Blood Supply

Rich blood supply is present. Arteries run parallel to the surface in the submucosa or

deep part of the reticular layer, and anastomose with adjacent vessels in the reticular layer

to form a, extensive capillary network in the papillary layer. From this network, capillary

loops pass into the connective tissue papillae and lie close to the basal layer. In cheek,

arterioles are tortuous with extensive branching. There is more profuse capillary loops than

in skin.

Blood flow:

Gingiva > Other oral mucosae > Skin

It lacks arteriovenous shunts. Due to rich anastomoses of arterioles and capillaries, it

has the ability to heal more rapidly after injury.

Nerve Supply

Oral mucosa is innervated densely. Nerves monitor all substances entering.

They also initiate and maintain voluntary and reflexive activities (involved in mastication,

salivation, swallowing, gagging, and speaking).

Efferent autonomic supply affects blood vessels and minor salivary glands. Nervesarise mainly from second and third divisions of the trigeminal nerve, facial (VII),


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glossopharyngeal (IX), and vagus (X) nerves. Sensory nerves lose their myelin sheaths to

form a network in the reticular layer of the lamina propria which terminates in a

subepithelial plexus.

Classification of Oral Mucosa

Oral mucus membrane can be classified into:

Masticatory

Lining

Specialized

Masticatory Mucosa

It covers areas exposed to compressive and shear forcesand to abrasion during the

mastication of food. It is found in hard palateand gingiva.

Histology:

Epitheliumis moderately thick and frequently orthokeratinized. Surfaces are

inextensible and withstand abrasion.

Junctionbetween epithelium and underlying lamina propria is convoluted with

numerous elongated papillae. This provides good mechanical attachment and

prevent the epithelium from being stripped off under shear force.

Thick lamina propriahas dense network of large, closely packed bundles of collagen

fibers, which follow a direct course between anchoring points. The tissue has little

slack and does not yield on impact, hence resist heavy loading.

Masticatory mucosa covers immobile structures and is bound firmly to them by

attachment of lamina propria. When it is directly attached to the periosteum of underlying

bone, it is known as mucoperiosteum. Indirectly it may be attached by a fibrous submucosa.

In lateral regions of palate, fibrous submucosa is interspersed with areas of fat and

glandular tissue, which cushion the mucosa against mechanical loads and protect the

underlying nerves and blood vessels.

Lining Mucosa

It covers the underside of the tongue, inside of the lips, cheeks, floor of the mouth,

and alveolar processes as far as the gingiva. The mucosa is subject to movement. These

regions, together with the soft palate, are classified as lining mucosa.

Histology:

Epithelium has larger thickness and is nonkeratinized. Surface is thus flexible and

able to withstand stretching.


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Interface with connective tissue is smooth. Slender connective tissue papillae may be

present

Lamina propria: Thicker with fewer collagen fibers, which follow a more irregular

course between anchoring points. Elastic fibers control the extensibility of the

mucosa.

Mucosa can be stretched to a certain extent before these fibers become taut and limit

further distention. As the mucosa becomes slack during masticatory movements, the elastic

fibers retract the mucosa toward the muscle and prevent it from bulging between the teeth

and being bitten.

Alveolar mucosa and mucosa covering the floor of the mouth are attached looselyto

the underlying structures by a thick submucosa. Mucosa of the underside of the tongue is

bound firmlyto underlying muscle. Soft palate is flexible but not highly mobile;mucosa is

separated from the loose and highly glandular submucosa by a layer of elastic fibers.

Specialized Mucosa

It includes the mucosa of the dorsal surface of the tongue. Functionally, it is a

masticatory mucosa, but also a highly extensible lining. It has different types of lingual

papillae.Some possess a mechanical function, whereas others bear taste buds (sensory

function).

Tongue mucosa is composed of two parts, divided by sulcus terminalis:

i.

Anterior two thirds (body) - derived from the first pharyngeal archii. Posterior third (base) - derived from the third pharyngeal arch

Extensive nodules of lymphoid tissue in the base of tongue are known as lingual tonsils.

a) Fungiform Papillae

Anterior portion of the tongue and tip

Fungiform = fungus-like

Single fungiform papillae scattered between the numerous filiform papillae

Smooth, round structures that appear red because of

Highly vascular connective tissue core Thin, nonkeratinized covering epithelium

Taste buds - present in the epithelium on the superior surface

b) Filiform Papillae

Cover entire anterior part of the tongue

Cone-shaped structures, each with a core of connective tissue covered by a thick

keratinized epithelium

Form a tough, abrasive surface

Compressing and breaking food

when the tongue is apposedto the hard palate


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Tongue is highly extensiblebecause of nonkeratinized, flexible epithelium

between the filiform papillae

Buildup of keratin results in elongation of the filiform papillae in some patients

The dorsum of the tongue then has a hairy appearance called hairy tongue

c)

Foliate Papillae

Leaf-like pink papillae

Lateral margins of the posterior part of the tongue

Few taste buds are present in the epithelium of the lateral walls of the ridges

Consist of parallel ridges that alternate with deep grooves in the mucosa

d) Circumvallate Papillae

Adjacent and anterior to the sulcus terminalis

Circumvallate = walled

8 to 12 papillae

Large structures each surrounded by a deep, circular groove into which open theducts of minor salivary glands (the glands of Ebner)

Connective tissue core covered on the superior surface by a keratinized

epithelium

Epithelium covering the lateral walls is nonkeratinized- contains taste buds

Taste Buds

They are specialized receptors which occur only in the oral cavity and pharynx. They

are found in the fungiform, foliate, and circumvallate papillae of the tongue.

Histology:

Barrel-shaped structure composed of 30 to 80 spindle-shaped cells

Separated from underlying connective tissue by the basal lamina

Apical ends terminate just below the epithelial surface in a taste pit

Communicates with the surface via taste pore

Cells:

They are of 3 types - light (type I), dark (type II), and intermediate (type III)

Type I - most common Type II - morphologically similar, contain numerous vesicles, adjacent to the

intraepithelial nerves

They are replaced continually. Their existence depends on presence of a functional

gustatory nerve. Initial events stimulating sensation of taste involve amorphous material

within the taste pits. The microvilli of constituent cells project into these pits.

Generation of taste stimuli:

1. Adsorption of moleculesonto membrane receptors on the surface

2.

Activation of signaling cascade mediated by membrane-associated proteins such astransducinand gustducin


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3. Change in membrane polarization

4. Release of transmitter substances

5. Stimulate unmyelinated afferent fibers of the glossopharyngeal nerve (IX)

Junctions in Oral Mucosa

Within the oral mucosa are three junctions that merit further discussion:

mucocutaneous (between the skin and mucosa),

mucogingival (between the gingiva and alveolar mucosa)

dentogingival (interface between the gingiva and the tooth)

The latter is of considerable anatomic and clinical importance because it represents the first

line of defense in periodontal diseases.

Mucocutaneous Junction

The skin is continuous with the oral mucosa at the lips. It is a transitional region

where appendages are absent except for a few sebaceous glands (situated mainly at the

angles of the mouth).

Epithelium is keratinized but thin, with long connective tissue papillae containing

capillary loops. This arrangement brings the blood close to the surface and accounts for the

strong red coloration in this region, called the red (or vermilion) zone of the lip. The line

separating the vermilion zone from the hair-bearing skin of the lip is called the vermilion

border.In young people this border is demarcated sharply, but as a person is exposed to ultraviolet

radiation, the border becomes diffuse and poorly defined. Because the vermilion zone lacks

salivary glands and contains only a few sebaceous glands, it tends to dry out, often

becoming cracked and sore in cold weather.

Between the vermilion zone and the thicker, nonkeratinized labial mucosa is an

intermediate zone covered by parakeratinized oral epithelium. In infants, this region is

thickened and appears more opalescent, which represents an adaptation to suckling called

the suckling pad.

Mucogingival Junction

Although masticatory mucosa meets lining mucosa at several sites, none is more

abrupt than the junction between attached gingiva and alveolar mucosa. This junction is

identified clinically by a slight indentation called the mucogingival groove and by the change

from the bright pink of the alveolar mucosa to the paler pink of the gingiva. Histologically, a

change occurs at this junction, not only in the type of epithelium but also in the composition

of the lamina propria.

The epithelium of the attached gingiva is keratinized or parakeratinized, and thelamina propria contains numerous coarse collagen bundles attaching the tissue to


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periosteum. The stippling seen clinically at the surface of healthy attached gingiva probably

reflects the presence of this collagen attachment, the surface of the free gingiva being

smooth.

The structure of mucosa changes at the mucogingival junction, where the alveolar

mucosa has a thicker, nonkeratinized epithelium overlying a loose lamina propria with

numerous elastic fibers extending into the thick submucosa. These elastic fibers return the

alveolar mucosa to its original position after distention by the labial muscles during

mastication and speech.

Coronal to the mucogingival junction is another clinically visible depression in the

gingiva, the free gingival groove, the level of which corresponds approximately to that of the

bottom of the gingival sulcus. This demarcates the free and attached gingivae, although

unlike the mucogingival junction, no significant change in the structure of the mucosa

occurs at the free gingival groove.

Development of Oral Mucosa

At 26 days of gestation, there is rupture of the buccopharyngeal membrane and

fusion of the embryonic stomatodeum with the foregut. This forms theprimitive oral

cavity. Epithelium covering structures that develop in the branchial arches (tongue,

epiglottis, pharynx) is derived from endoderm, while epithelium covering the palate,

cheeks, and gingivae are ectodermal in origin.

At 5 to 6 weeks of gestation, a single layer of lining cells forms two cell layers.

At 8 weeks of gestation, there is thickening of the vestibular dental lamina complex By 10 to 14 weeks, cellular degeneration occurs at central region of this thickening.

This causes separation of the cells covering the cheek area and the alveolar mucosa,

which forms the oral vestibule.

By 8 to 11 weeks, the palatal shelves elevate and closure occurs.

By 7 weeks, the lingual epithelium shows specialization. The circumvallate and

foliate papillae first appear, followed by the fungiform papillae. The taste buds soon

develop.

By 10 weeks, the filiform papillae become apparent.

By 10 to 12 weeks, the future lining and masticatory mucosa show stratification of

epithelium. Between 13 and 20 weeks, all the oral epithelia thicken and there is appearance of

sparse keratohyalin granules. During this period, melanocytes and Langerhans cells

appear in the epithelium. Surface layers of the epithelium show parakeratosis.

Orthokeratinization does not occur until after teeth erupt.

Initially, ectomesenchyme consists of widely spaced stellate cells in an amorphous

matrix

By 6 to 8 weeks, extracellular reticular fibers accumulate

Between 8 and 12 weeks, capillary buds and collagen fibers can be detected. As

collagen fibers increase in number, they are arranged in the form of bundles.

Between 17 and 20 weeks, the elastic fibers become prominent in the connectivetissue of lining mucosa.


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Age Changes

Smoother and dryer surface - atrophic or friable

Epithelium appears thinner

Flattening of epithelial ridges - smoothing of the epithelium-connective tissueinterface

Dorsum of the tongue - reduction in the number of filiform papillae - smooth or

glossy appearance

Reduced number of filiform papillae - make fungiform papillae more prominent -

erroneously considered a disease

Decreased rates of metabolic activity

Langerhans cells become fewer - decline in cell-mediated immunity

Vascular changes may be prominent, with the development of varicosities

Nodular varicose veins on the undersurface of the tongue (sometimes called caviartongue)

Lamina propria - a decreased cellularity occurs and increased amount of collagen,

which becomes more highly cross-linked

Sebaceous glands (Fordyces spots) of the lips and cheeks also increase

Minor salivary glands - atrophy with fibrous replacement

Elderly patients, particularly postmenopausal women, may have symptoms such as

dryness of the mouth, burning sensations, and abnormal taste

References1. Tencates Oral Histology 8

thEdition

2. Orbans Oral Histology & Emrbyology 13th

Edition

3. Grays Anatomy for Students 2nd

Edition

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