Cui Dongmei. Atlas of Histology: with functional and clinical correlations. 1st ed

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CHAPTER 13

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Integumentary System

255

Development of the Skin

SYNOPSIS 13-2 Pathological Terms for the Integumentary System

Acanthosis ■ : Thickening of the stratum spinosum of the epidermis, typically seen in epidermal hyperplasia.

Hypergranulosis

■ : Thickening and prominence of the stratum granulosum of the epidermis, often in response to chronic

mechanical irritation of the skin. Hypergranulosis may also be seen in the declivities of papillary lesions such as verruca

vulgaris, or warts.

Hyperkeratosis

■ : Thickening of the stratum corneum of the epidermis. Orthokeratotic hyperkeratosis refers to hyperkeratosis

without the presence of nuclei.

Papillomatosis

■ : Fingerlike projections from the epidermal surface, often with hyperkeratosis, seen in a variety of conditions

including verruca vulgaris, or warts.

Parakeratosis

■ : A form of hyperkeratosis in which nuclei are retained in the stratum corneum, seen in many conditions

including psoriasis.

Spongiosis

■ : Intercellular edema of the epidermis frequently seen in various etiologies of dermatitis such as allergic contact

dermatitis or irritant dermatitis.

Ulceration

■ : The discontinuity of an epithelial surface including the epidermis or mucous membranes.

Figure 13-12A. Fetal skin (5–9 weeks). H&E, 331

The two layers (epidermis and dermis) of the skin develop from two

different embryonic tissues. The epidermis develops from the ecto-

derm, and the dermis from the mesoderm. About 4 weeks after con-

ception, the human embryo is covered by a single layer of ectodermal

cells, which are loosely arranged on the basement membrane and

over the mesenchymal tissue. After 5 weeks, the epidermis has two

layers of cells: the superﬁ cial layer (periderm) and basal layers. At

2 to 3 months, basal cells are dividing rapidly, and the epidermis

becomes several cell layers thick. At the same time, the mesenchyme

differentiates into a more mature connective tissue with blood

vessels. By 4 months, neural crest cells migrate into the basal layer of

the epidermis and differentiate into melanocytes and Merkel cells.

The connective tissue layer beneath the epithelium develops into

the dermis and a deeper layer, the hypodermis. At about 5 months,

the appendages of the skin (hair follicles and glands) start to form.

This section shows an early stage of skin development in an embryo.

There are only two layers of epithelial cells in the epidermis, and fetal

blood vessels are located within the mesenchyme tissue. Nucleated

erythrocytes are shown inside the blood vessels.

Periderm

Basement

membrane

Basement

membrane

Mesenchymal

tissue

Mesenchymal

tissue

Nucleated

erythrocytes

Nucleated

erythrocytes

Mesenchymal

cells

Mesenchymal

cells

Basal layer

Figure 13-12B. Fetal skin (ﬁ fth month). H&E, 438

This section shows a later stage of fetal skin development. The

epidermis has formed multiple cell layers, and four layers of epi-

dermis can be distinguished to some extent. The basal cells in

the stratum basale layer are highly active and appear as column-

shaped cells. The underlying mesenchymal tissue has differentiated

into connective tissue (dermis). There are many active ﬁ broblasts

in the dermis. An accumulation of basal cells forms a fold called

an epidermal bud, which projects into the dermis. These accu-

mulated cells will interact with the dermis and differentiate into

appendages (hair follicles and glands).

Epidermis

Dermis

Accumulated

basal cells

(epidermal bud)

Accumulated

basal cells

(epidermal bud)

Erythrocytes in

the blood vessels

Erythrocytes in

the blood vessels

Basal cells

Fibroblasts

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256

Oral Cavity

Oral Mucosa

Introduction and Key Concepts for Oral Mucosa

Figure 14-1 Overview of the Oral Mucosa and Teeth

Lining Mucosa

Figure 14-2A Overview of the Lip

Figure 14-2B Skin, Lip

Figure 14-2C Vermilion Zone, Lip

Figure 14-2D Labial Mucosa (Lining Mucosa), Lip

Figure 14-3A Buccal Mucosa (Lining Mucosa), Cheek

Figure 14-3B Clinical Correlation: Oral Submucous Fibrosis of the Lip

Table 14-1 Comparison of Lining and Masticatory Mucosae

Masticatory Mucosa

Figure 14-4A Masticatory Mucosa, Gingiva

Figure 14-4B Masticatory Mucosa, Hard Palate

Figure 14-4C Clinical Correlation: Nicotine Stomatitis

Specialized Mucosa

Figure 14-5A Overview of the Tongue

Figure 14-5B Filiform Papillae, Tongue

Figure 14-5C Fungiform Papillae, Tongue

Figure 14-6A Circumvallate Papillae, Tongue

Figure 14-6B Foliate Papillae and Taste Buds, Tongue

Table 14-2 Comparison of Lingual Papillae

Teeth

Introduction and Key Concepts for Teeth

Figure 14-7 Overview of the Teeth

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257

Tooth Development (Odontogenesis)

Figure 14-8 Overview of Tooth Development (Odontogenesis)

Figure 14-9A Bud Stage, Weeks 8–9

Figure 14-9B Cap Stage, Weeks 10–11

Figure 14-10A Bell Stage, Weeks 12–14

Figure 14-10B Bell Stage, Cell Layers

Figure 14-11A Apposition (Crown) Stage, Dentinogenesis

Figure 14-11B Apposition (Crown) Stage, Amelogenesis

Figure 14-12A Tooth Root Development

Figure 14-12B Tooth Eruption

Figure 14-12C Clinical Correlation: Dilaceration

Figure 14-13A Clinical Correlation: Gemination, Incisor

Figure 14-13B Clinical Correlation: Amelogenesis Imperfecta

Figure 14-13C Clinical Correlation: Enamel Pearl

Enamel, Dentin, and Dental Pulp

Figure 14-14A,B Enamel, Tooth

Figure 14-14C Clinical Correlation: Enamel Fluorosis

Figure 14-15A,B Dentin, Tooth

Figure 14-15C Clinical Correlation: Dentinogenesis Imperfecta

Figure 14-16A Clinical Correlation: Vitamin D–Resistant Rickets

Figure 14-16B Clinical Correlation: Dentin Dysplasia

Table 14-3 Dental Hard Tissue

Figure 14-17A,B Dental Pulp

Figure 14-17C Clinical Correlation: Pulp Abscess

Periodontium

Figure 14-18A Acellular Cementum, Cervical Region of Tooth Root

Figure 14-18B Cellular Cementum, Apical Region of Tooth Root

Figure 14-18C Periodontal Ligament and Alveolar Bone

Figure 14-19A Periodontal Ligament and Alveolar Bone, Tooth Root

Figure 14-19B Clinical Correlation: Tooth Ankylosis

Synopsis 14-1 Pathological and Clinical Terms for the Oral Cavity

Oral Mucosa

Introduction and Key Concepts for Oral

Mucosa

The oral cavity refers to the internal part of the mouth and can

be divided into the oral vestibule and the oral cavity proper.

The oral vestibule is the space between the inner lips, cheeks,

and front surface of the teeth. The oral cavity proper is the space

between the upper and lower dental arches, extending from the

inner surface of the teeth to the oropharynx. The structures

inside of the oral cavity include the lips, cheeks, tongue, teeth,

gingiva, palates (hard and soft), salivary glands, and tonsils. The

tonsils are discussed in Chapter 10, “Lymphoid System,” and

salivary glands are discussed in Chapter 16, “Digestive Glands

and Associated Organs.” The structures in the oral cavity are

lined by an oral mucosa, which includes an overlying epithe-

lium and underlying connective tissue. The oral mucosa can be

divided into three types based on differences in the epithelial

covering, organization of the connective tissue, and associated

functions: lining, masticatory, and specialized mucosa.

LINING MUCOSA is covered by nonkeratinized stratiﬁ ed

squamous epithelium with two distinct layers: the stratum basale

and stratum spinosum. The epithelium of the lining mucosa is

similar to the epidermis of the skin, except that it has neither

a stratum corneum nor a stratum lucidum, and the stratum

granulosum is often absent (see Chapter 13, “Integumentary

System,” Figs. 13-2 and 13-3B). The nonkeratinized stratiﬁ ed

epithelium is moistened by saliva. The connective tissues of the

lining mucosa can be divided into the lamina propria and the

submucosa. The lamina propria is a thin layer of loose connec-

tive tissue containing many elastic ﬁ bers and relatively few col-

lagen ﬁ bers. This layer is equivalent to the dermis of the skin

and is located beneath the epithelium. The submucosa is a thick

layer of connective tissue, which contains minor salivary

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Organ Systems

glands and is attached to the underlying muscle. The lining

mucosa covers the inner oral surfaces of the lips, cheeks, soft

palate, the inferior surface of the tongue, and the ﬂ oor of the

mouth. This type of mucosa is less exposed to abrasion than

the masticatory mucosa. The lining mucosa provides a bar-

rier against the invasion of pathogens and toxic chemicals,

contains receptors for sensations, and serves immunological

functions. The lining mucosa also provides lubrication and

buffering by minor glands in the submucosal layer. Examples

of the lining mucosa include the lip (Fig. 14-2D) and cheek

(Fig. 14-3A).

MASTICATORY MUCOSA is covered by keratinized strati-

ﬁ ed squamous epithelium, which is exposed to signiﬁ cant abra-

sion due to high compression and friction during chewing.

The epithelium of the masticatory mucosa is composed of the

stratum basale, stratum spinosum, stratum granulosum, and

stratum corneum. It has a thick lamina propria that contains a

dense network of collagen ﬁ bers and a few elastic ﬁ bers. This

layer has no submucosa and is directly and ﬁ rmly attached to

the underlying bone. Masticatory mucosa can be found cover-

ing the oral surfaces of the gingiva and the hard palate. Injec-

tion into this area is difﬁ cult and painful because of its sensitive

periosteum, high collagen density, and ﬁ rm attachment to the

bone. See Figure 14-4A for examples of the gingiva and Figure

14-4B for the hard palate.

SPECIALIZED MUCOSA covers the anterior two thirds of

the tongue and consists of keratinized and nonkeratinized

squamous epithelium and numerous papillae. These papillae

can be classiﬁ ed into four types: ﬁ liform, fungiform, circum-

vallate, and foliate papillae. Most of these papillae have taste

buds. The ﬁ liform papillae are the only papillae without taste

buds; their main function is to aid in mixing food during chew-

ing. The lamina propria (connective tissue) of the specialized

mucosa is attached to the underlying skeletal muscle. These

muscles produce voluntary movement of the tongue and are

innervated by the hypoglossal nerve (cranial nerve [CN] XII).

Lining mucosa covers the inferior surface of the tongue. The

mucosa of the tongue is divided into two parts by a V-shaped

groove called the sulcus terminalis. The anterior two thirds of

the tongue is referred to as the body of the tongue. Its mucosa

is innervated by the facial nerve (CN VII) and the trigeminal

nerve (CN V). The posterior third of the tongue is the base of

the tongue. Its taste buds and mucosa are innervated by the

glossopharyngeal nerve (CN IX). The posterior third of the

tongue contains the lingual tonsils (Fig. 14-5A).

1. Filiform papillae are the smallest and most numerous of the

four types of papillae. They cover almost the entire supe-

rior surface of the anterior two thirds of the tongue and

are packed in rows that parallel the sulcus terminalis. Each

of the papillae appears cone shaped with some branching

processes. Connective tissue forms the central core of each

papilla. Filiform papillae have no taste buds and extend

from the nonkeratinized stratiﬁ ed squamous epithelium.

The surface of the papilla is keratinized and is exposed to a

great deal of abrasion (Fig. 14-5B).

2. Fungiform papillae are less numerous than the ﬁ liform

papillae. They are mushroom shaped and are scattered

among the ﬁ liform papillae (Fig. 14-5C). Fungiform papil-

lae are located at the tip and on the two lateral edges of the

tongue. They are more numerous near the tip of the tongue.

Taste buds are found on the apical surfaces of fungiform

papillae.

3. Circumvallate papillae are large and round with a ﬂ at-

topped cylindrical structure. There are about 10 to 14

papillae arranged in a row along the sulcus terminalis. Each

papilla is surrounded by a deep groove (moat), which forms

a valley around the papilla. Taste buds are found in the lat-

eral walls of each papilla (Fig. 14-6A).

4. Foliate papillae are leaﬂ ike folds with ﬂ at tops and have deep

clefts between the papillae. They are located on the posterior

lateral surface of the tongue. They are more prominent in

some animals (such as rabbits) than in humans. Foliate

papillae contain taste buds in the lateral walls of the papillae

(Fig. 14-6B).

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259

The oral cavity is lined by oral mucosa, which can be divided into masticatory mucosa (gingiva, hard palate), lining mucosa (lips,

soft palate, cheeks, inferior surface of the tongue, ﬂ oor of the mouth), and specialized mucosa (tongue). This illustration represents

the lip and a tooth and the mucosa covering these structures. The lip is covered externally with skin to the vermilion zone (inter-

mediate zone or mucocutaneous junction); the vermilion zone continues to the labial mucosa, which is the lining mucosa on the

internal surface of the lip. The alveolar process of the jaw (containing the tooth roots) is covered by alveolar mucosa (lining mucosa)

and gingiva. The junction between the lining mucosa and gingiva is the mucogingival junction. The tooth can be divided into three

parts: crown, cervix, and root. The crown is the part of the tooth projecting into the oral cavity and has two different deﬁ nitions:

The clinical crown is the part of the crown which is visible in the mouth; the anatomical crown is the part of the tooth covered by

enamel. The root is covered by the gingiva or is inside the bony socket. The region between the crown and root is the cervix (neck).

The gingival sulcus is the space between the free gingiva and the enamel; it is normally 0.5 to 3.0 mm in depth.

Alveolar (lining)

mucosa

Alveolar (lining)

mucosa

Dentin

Apical foramen

Alveolar bone

(process)

Alveolar bone

(process)

Cervix

Root

Crown

Gingiva

Dental pulp

l c

Anatomic

l crown

Clinical crown

Clinical

crown

Clinical crown

Enamel

Dentin

Labial (lining)

mucosa

Labial (lining)

mucosa

Dentogingival

junction

Mucogingival

junction

Gingiva

(masticatory mucosa)

Vermilion zone

(intermediate zone

mucocutaneous

junction)

Skin

Enamel

space

Enamel

space

Sulcus

epithelium

Sulcus

epithelium

Free gingiva

Gingiva sulcus

Gingival

epithelium

Junctional

epithelium

Alveolar

bone

labial sulcus

ial su

Labial sulcus

Figure 14-1. Overview of the oral mucosa and teeth. Lower left, H&E, 18

If the depth of the gingival sulcus is over 3 mm, these spaces are called gingival or periodontal pockets. These pockets represent

an abnormal condition. An accumulation of debris and microbes in the pockets may cause damage to the periodontal ligament

(PDL). For tooth details, see Figure 14-7.

I. Lining mucosa (covering of inner surface of the lips and

cheeks, soft palate, inferior surface of the tongue, and ﬂ oor

of the mouth)

A. Epithelium: nonkeratinized stratiﬁ ed squamous epithelium

B. Lamina propria: connective tissue with many elastic ﬁ bers

and few collagen ﬁ bers

C. Submucosa: connective tissue with minor salivary glands

and their ducts

II. Masticatory mucosa (covering of gingiva and hard palate)

A. Epithelium: keratinized stratiﬁ ed squamous epithelium

B. Lamina propria: connective tissue with few elastic ﬁ bers

and many dense collagen ﬁ bers

C. No submucosa

III. Specialized mucosa (tongue)

A. Filiform papillae: no taste buds

B. Fungiform papillae: taste buds on apical surface of the

papilla—sweet, sour, salty

C. Circumvallate papillae: taste buds in lateral wall of the

papilla—bitter

D. Foliate papillae: taste buds in lateral wall of papilla

Structures of the Oral Mucosa

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Organ Systems

Lining Mucosa

Figure 14-2A. Overview of the lip, H&E, 7.6

Lining mucosa is a wet mucosa that covers the inside of the mouth

and is lined by nonkeratinized stratiﬁ ed squamous epithelium.

The labial mucosa of the lip is an example of lining mucosa. The

lips are soft, ﬂ exible, and movable; they play important roles in

food intake, speech, and as a sensory organ (e.g., kissing). Lips

can be divided into three regions: (1) thin skin, forming the exter-

nal surface of the lip; (2) vermilion zone, appearing red in color,

also called the intermediate zone or mucocutaneous junction;

and (3) the labial mucosa (lining mucosa), the internal surface

of the lip. The central core of the lip contains the orbicularis oris

(skeletal) muscle, which is innervated by the facial nerve (CN

VII), and contributes to lip movement and facial expressions.

Labial

(lining)

mucosa

Fig.

14-2D

Vermilion

zone

Minor

salivary gland

Fig.

14-2C

Vermilion

zone

Skin

Fig.

14-2B

ris

Orbicularis

oris muscle

Orbicularis

oris muscle

Orbicularis

oris muscle

Sweat

glands/ducts

Sweat

glands/ducts

Sebaceous

glands

Sebaceous

glands

Sebaceous

glands

Sebaceous

glands

Sweat

glands/ducts

Sweat

glands/ducts

Hair

follicle

space

Hair

follicle

Epidermis

Dermis

Figure 14-2B. Skin, lip. H&E, 33; inset 44

An example of the skin on the external surface of the lip is shown.

It is covered by keratinized stratiﬁ ed squamous epithelium. The

sebaceous glands in the dermis are associated with hair follicles,

and sweat glands are present. The skin of the lip is like thin skin

elsewhere and can be divided into epidermis and dermis.

Ducts of sebaceous-like

glands

Ducts of sebaceous-like

glands

Fordyce granules/spots

ebaceous-like glands

)

Fordyce granules/spots

ebaceous-like glands(s )

Parakeratinized stratified

squamous epithelium

Nonkeratinized stratified

squamous epithelium

Nonkeratinized stratified

squamous epithelium

Ducts of minor

salivary glands

Ducts of minor

salivary glands

Stratum

spinosum

Stratum

spinosum

Stratum

basale

Stratum

basale

Minor

salivary

glands

Minor

salivary

glands

Figure 14-2C. Vermilion zone, lip. H&E, 33

The vermilion zone of the lip is covered by parakeratinized strati-

ﬁ ed squamous epithelium. Sebaceous-like glands (Fordyce gran-

ules or spots) may be found in the connective tissue and are not

associated with hair follicles. These glands have ducts that release

their oily product directly onto the surface of the lip. The ver-

milion zone appears red because of many blood vessels near the

surface of the thin and translucent epithelium (Fig. 14-1). This

region can become thick and forms the sucking pad in infants.

Figure 14-2D. Labial mucosa (lining mucosa), lip. H&E, 33

The labial mucosa of the lip is an example of lining mucosa,

which is covered by nonkeratinized stratiﬁ ed squamous epithe-

lium and contains many elastic ﬁ bers; it is very ﬂ exible and can

be stretched. Its submucosa layer contains many minor salivary

glands (mucous glands). The minor salivary glands in the lips are

often called labial glands.

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261

Name of

Mucosa

Epithelium Lamina Propria Submucosa Covering

Region

Special

Features

Clinical Application

Lining

mucosa

Nonkeratinized

stratiﬁ ed

squamous

epithelium

Few collagen

ﬁ bers; many

elastic ﬁ bers

Well-developed

submucosa;

attached

primarily to

underlying muscle

rather than

bone (except for

alveolar mucosa)

Lips, cheeks,

soft palate,

inferior surface

of the tongue,

and ﬂ oor of the

mouth

Thick, soft,

and loose;

ﬂ exible

and can be

stretched

Injections are easy to

make and minimally

painful; if cut, a gap

appears that requires

suturing; infection

spreads quickly

Masticatory

mucosa

Keratinized

stratiﬁ ed

squamous

epithelium

Dense network

of collagen ﬁ bers;

few elastic ﬁ bers

No submucosa

present; lamina

propria is directly

and ﬁ rmly bound

to the bone

Gingiva, hard

palate

Thin, stiff,

dense;

cannot be

stretched

Injections are difﬁ cult

and painful; if cut,

no gap results and

suturing is not

necessary; infection

spreads slowly

TABLE 14-1 Comparison of Lining and Masticatory Mucosae

CLINICAL CORRELATION

Figure 14-3B.

Oral Submucous Fibrosis of the Lip.

H&E, 25

Oral submucous ﬁ brosis is a precancerous condition char

acterized by a mucosal rigidity due to ﬁ broelastic changes

of the lamina propria and submucosa layers of the lining

mucosa. This causes a progressive difﬁ culty in opening

the mouth. It affects the buccal mucosa, lips, retromolar

areas, the soft palate, and even the esophagus. Causes of

this condition include the use of chillies and areca nut,

collagen disorders, and autoimmune disorders. Histologi-

cally, it is characterized by atrophic (thinned) epithelium

and increased collagen ﬁ ber formation followed by the

presence of dense collagen ﬁ ber bundles and different

degrees of hyalinization. Prevention and treatments of the

disease include dietary changes and having plastic surgery

to improve the function of the mouth.

Atrophic

epithelium

Increased

collagen fibers

Elastic fibers

Lamina

propria

Lamina

propria

Stratum

basale

Stratum

basale

Stratum

spinosum

Stratum

spinosum

Stratum

granulosum

Stratum

granulosum

Nonkeratinized stratified

squamous epithelium

Figure 14-3A. Buccal mucosa (lining mucosa), cheek.

H&E, 16

Each cheek constitutes a lateral wall of the mouth. The inner

surface of the cheeks is lined by lining mucosa known as buccal

mucosa. The buccal mucosa has a nonkeratinized stratiﬁ ed

squamous epithelium with three deﬁ nite layers (stratum basale,

spinosum, and granulosum) with many elastic ﬁ bers in the

lamina propria and minor salivary glands (buccal glands) in the

submucosa layer. This example shows the epithelium and lam-

ina propria of the buccal mucosa, which has a nonkeratinized

stratiﬁ ed squamous epithelium. There are many elastic ﬁ bers in

the lamina propria of the mucosa. Elastic ﬁ bers appear pink and

do not readily stain with H&E stain. Fordyce spots (sebaceous-

like glands) may also be found in the mucosa of the cheek. They

increase with age and are more visible in elderly individuals.

The lingual and inferior alveolar nerves run through the pos-

terior groove of the cheek (between the pterygomandibular

raphe and the ramus of the mandible). This is an important

landmark for local anesthesia injections in the mouth.

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Organ Systems

Masticatory Mucosa

Alveolar bone

Mucogingival

junction

Mucogingival

junction

Enamel space

Junction epithelium

Junction epitheliumJunction epithelium

Junction epithelium

Sulcus epithelium

Sulcus epitheliumSulcus epithelium

Sulcus epithelium

Free

gingiva

ttached

gingiva

Alveolar

mucosa

ria

Lamina propria

Dentin

Dental

pulp

Dental

pulp

Cementum

Figure 14-4A. Masticatory mucosa, gingiva. H&E, 22

Masticatory mucosa covers the gingiva and hard palate; it has a

keratinized stratiﬁ ed squamous epithelium, which is exposed to

more abrasion during chewing than the lining mucosa. Mastica-

tory mucosa lacks a submucosa layer. The lamina propria of the

masticatory mucosa consists of a dense network of collagen ﬁ bers

that are ﬁ rmly attached to the underlying bone. The gingiva (gum)

surrounds the cervix of the tooth and covers the upper part of the

alveolar bone at the tooth root. The gingiva can be divided into

free gingiva and attached gingiva. The superior part of the gingiva

is free gingiva and surrounds, but does not attach to, the cervix of

the tooth. This nonattachment between the sulcus epithelium of the

free gingiva and enamel creates a space called the gingival sulcus, or

free gingival groove, (normally 0.5–3 mm depth). The attached gin-

giva ﬁ rmly attaches to the underlying hard tissues (alveolar bone,

cementum, and edge of the enamel). The gingival-mucosal border

is called the mucogingival junction (see Fig. 14-1), where the epi-

thelium changes from nonkeratinized to keratinized and the color

changes from bright pink (alveolar mucosa) to pale pink (gingiva).

Stratum

basale

Stratum

basale

Stratum

granulosum

Stratum

granulosum

Stratum corneum

Stratum

spinosum

Stratum

spinosum

Keratinized stratified

squamous epithelium

Lamina

propria

Lamina

propria

Collagen

fibers

Collagen

fibers

Figure 14-4B. Masticatory mucosa, hard palate. H&E, 35

The hard palate forms the roof of the mouth and is covered

by masticatory mucosa with keratinized stratiﬁ ed squamous

epithelium and a dense lamina propria. It has one more layer

(stratum corneum) than the lining mucosa. The collagen ﬁ bers in

the lamina are thick and dense and ﬁ rmly bind to the periosteum

of the underlying bone. The periosteum consists of dense connec-

tive tissue, which covers the bone and contributes to bone forma-

tion (see Chapter 5, “Cartilage and Bone,” Fig. 5-10B). Most of

the hard palate lacks a submucosal layer. However, the posterior

region near the alveolar process may present a submucosal layer

that contains minor mucous glands. The hard palate signiﬁ cantly

assists in mastication and speech.

Cleft palate is a birth defect in which there is a ﬁ ssure in the hard

palate that is caused by the failure of two parts of the palate

to fuse during facial development. This condition impairs the

quality of speech (an individual is unable to pronounce certain

sounds) and also causes eating problems.

CLINICAL CORRELATION

Acanthosis

Orifice of the

gland ducts

Minor salivary

glands

Hyperkeratosis

Acanthosis

Figure 14-4C.

Nicotine Stomatitis. H&E, 25

Nicotine stomatitis is a nonprecancerous condition characterized

by a white lesion in the oral mucosa of the hard palate of the

mouth. The causes of this condition are associated with long-

term tobacco smoking, especially pipe smoking, and hot beverage

consumption. The lesion has a white cobblestone or “dried-

mud” appearance because of excessive keratin production. The

hard palate may appear gray or white and contain many papules

that are slightly elevated with red in their center. Histologically,

the squamous mucosa demonstrates hyperkeratosis (thickening

of the stratum corneum) and acanthosis (overgrowth of the

stratum spinosum). Complete smoking cessation usually helps

to diminish and resolve the condition within about two weeks. If

the lesion persists, close monitoring may be necessary.

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263

Specialized Mucosa

T. Yang

Foliate

papillae

Circumvallate

papillae

Lingual

tonsil

Palatine

tonsil

Fungiform

papillae

Filiform

papillae

Fig. 14-5B

Fig. 14-6A

Fig. 14-5C

Sulcus

terminalis

Palatoglossus

muscle

Oropharynx

Figure 14-5A. Overview of the tongue.

The inferior surface of the tongue and the ﬂ oor of the mouth

are covered by lining mucosa with a nonkeratinized squamous

epithelium. The superior surface of the tongue is covered by

specialized mucosa with numerous projecting papillae includ-

ing ﬁ liform papillae, fungiform papillae, circumvallate papillae,

and foliate papillae. The specialized mucosa is attached to the

underlying skeletal muscle. The tongue has a central core of

skeletal muscle, which controls movements of the tongue and

is innervated by the hypoglossal nerve (CN XII). The base of

the tongue is attached to the ﬂ oor of the mouth. The surface

of the posterior third of the tongue has somatosensory recep-

tors and taste buds that are innervated by the glossopharyn-

geal nerve (CN IX). The anterior two thirds of the tongue has

somatosensory receptors that are innervated by the trigeminal

nerve (CN V), and its taste buds are innervated by the facial

nerve (CN VII). The tongue plays an important role in speech,

taste, and in moving and swallowing (deglutition) food.

Filiform

papillae

Epithelium

Lamina propria

Skeletal

muscle

Figure 14-5B. Filiform papillae, tongue. H&E, 35

The ﬁ liform papillae are slender, cone-shaped papillae with

keratinized outer surfaces. They are the most numerous but

smallest in size of the four types of papillae. The ﬁ liform

papillae are often packed in rows and cover the entire supe-

rior surface of the anterior two thirds of the tongue (anterior

to the sulcus terminalis). Each ﬁ liform papilla has a central

connective tissue core with several branches of small papillae.

They are the only papillae that do not have taste buds. The

ﬁ liform papillae’s tips are keratinized, consistent with their

exposure to abrasion during chewing. Because they have no

taste buds, their main functions are to help with chewing and

mixing food. The submucosal layer is absent in the tongue;

the mucosa of the tongue is strongly bound to the underlying

skeletal muscle to allow optimum food bolus control.

Fungiform papilla

Filiform

papillae

ria

ith

liu

Epithelium

Skeletal

muscle

Skeletal

muscle

ria

Lamina propria

Figure 14-5C. Fungiform papillae, tongue. H&E, 44

The fungiform papillae are mushroom shaped and much less

numerous than the ﬁ liform papillae. They tend to be slightly

taller than the ﬁ liform papillae that surround them. Each

fungiform papilla has one to ﬁ ve taste buds on its superior sur-

face. These taste buds are innervated by the chorda tympani

branch of the facial nerve (CN VII), which joins the lingual

branch of the trigeminal nerve (CN V). The fungiform papillae

are covered by nonkeratinized squamous epithelium. They are

distributed at the tip and two sides of the tongue (Fig. 14-5A).

In general, the taste buds have ﬁ ve taste sensations: sweet, bit-

ter, umami, salty, and sour. The salty and sour sensations are

associated with ion channels; the other three taste sensations

are associated with G protein–coupled receptors.

CUI_Chap14.indd 263 6/2/2010 8:23:07 AM

264

UNIT 3

■

Organ Systems

Moat (groove)

Lateral wall

(taste buds)

Lateral wall

(taste buds)

Duct of the

Von Ebner glands

Duct of the

Von Ebner glands

Von Ebner

glands

Von Ebner

glands

Taste buds

Circumvallate

papilla

Figure 14-6A. Circumvallate papillae, tongue. H&E,

34 inset 181

The circumvallate papillae are also called vallate papillae.

They are arranged in a single row, which contains about

10 to 14 papillae that are located immediately anterior to the

sulcus terminalis (Fig. 14-5A). Each circumvallate papilla is

cylindrical in shape and is surrounded by a groove called a

moat. The ducts of the glands of von Ebner (minor serous

salivary glands) open and drain serous products into the

groove; this helps to clear the food debris in the groove and

helps in detection of taste. Most minor salivary glands in the

oral cavity are mucous or mixed glands; von Ebner glands

are the only ones that are pure serous glands. The taste buds

of the circumvallate papillae are located on the lateral walls

of the groove. These taste buds are mainly bitter receptors

and are innervated by the glossopharyngeal nerve (CN IX).

Foliate

papilla

Taste receptor cell

Taste pore

Basal cell

Taste buds

Figure 14-6B. Foliate papillae and taste buds, tongue.

H&E, 68 inset 222

The foliate papillae are located on the posterior lateral

surface of the tongue. This type of papilla is not well devel-

oped in humans but is frequently found in animals; illus-

trated here from rabbit tissue.

In general, taste buds are ovular structures embedded

in nonkeratinized stratiﬁ ed squamous epithelium of the

papillae of the tongue. They also can be found in the pal-

ate of the oral cavity and in the mucosa of the oropharynx

and epiglottis. Each taste bud is composed of 40 to 60 elon-

gated taste receptor cells with microvilli at the apical region,

which extend into the taste pore. The basal end of the taste

bud contacts an afferent nerve ﬁ ber. The taste pore is a small

opening that allows taste molecules to contact taste recep-

tor cells. The taste receptor cells have a life span of 1 to

2 weeks, and new taste cells arise from basal cells at the basal

lateral region of the taste bud. The inset shows taste buds.

Name Epithelial Covering Taste Buds Location Main Function

Filiform papillae Keratinized stratiﬁ ed

squamous epithelium

No taste buds Anterior 2/3 of tongue Helps in chewing and

mixing food

Fungiform papillae Nonkeratinized stratiﬁ ed

squamous epithelium

Taste buds located at

the apical surface of

papillae

Tip and two sides of

tongue

Chemoreceptor

detecting taste

Circumvallate papillae Nonkeratinized stratiﬁ ed

squamous epithelium

Taste buds located at

the lateral surface of

papillae

In a V-shaped row just

anterior to the sulcus

terminalis

Chemoreceptor

detecting taste

Foliate papillae Nonkeratinized stratiﬁ ed

squamous epithelium

Taste buds located at

the lateral surface of

papillae

Posterior lateral

surface of the tongue

Chemoreceptor

detecting taste

TABLE 14-2 Comparison of Lingual Papillae

CUI_Chap14.indd 264 6/2/2010 8:23:11 AM