A reminder of things we should already remember

A reminder of things we should already remember but have completely forgotten

Oral Mucosa -lining of the oral cavity -mucosal membrane = epithelium + connective tissue -derived from the ectoderm -epithelium = stratified squamous ( skin equivalent = epidermis) -connective tissue = lamina propria (skin equivalent = dermis) -lamina propria = thin, vascular layer of connective tissue below the epithelium of an oral mucosa -comprised of collagen fibers -comprised of two layers 1. an upper papillary layer – associated with epithelial ridges 2. a lower reticular layer – thicker bundles of CN fibers that lie in parallel -in between these tissues = basement membrane -below the connective tissue lamina propria = submucosa -for attachment to bone

Oral mucosa classifications • Lining mucosa – buccal mucosa, labial mucosa, alveolar mucosa, floor of the mouth, ventral tongue, soft palate – non-keratinized stratified squamous epithelium – soft, moist, ability to stretch and compress • Masticatory mucosa – attached gingiva, hard palate, dorsal tongue – rubbery, resilient – keratinized or parakeratinized stratified squamous epithelium • Specialized – dorsal tongue surface – associated with the lingual papillae

Representative Mucosa -the interface between the epithelium and LP interdigitates -upward projections of the LP are called connective tissue ridges or papillae (dermal papillae in skin) -downward ridges of the epithelium are called rete ridges or pegs underside of epithelium connective tissue ridges

Epithelium -four types of cells 1. epithelial cells (in keratinized epithelium = keratinocyte) -rapidly renewing through differentiation of basal/stem cells -formation of a cohesive sheet that resists physical forces and serves as a physical barrier -connection through desmosomes & gap junctions 2. Langerhans cells – immune cells -dendritic cells 3. Granstein cells – similar to Langerhans 4. Merkel cells – pressure 5. melanocytes – dendritic cell of neural crest origin (ectodermal) -synthesis the light absorbing pigment melanin

Epithelium: Non-keratinized vs. Keratinized -three types of squamous epithelium 1. non-keratinized 2. para-keratinized 3. keratinized or orthokeratinized -all three of these share many similarities -similar types of cells found in distinct layers 1. basal 2. prickle 3. granular 4. keratinized

1. basal layer or stratum germinativum (epidermis): -inner most layer of cuboidal or columnar cells -in the thin mucosa of the floor of the mouth = one layer -in the cheeks and palate = 2 or 3 layers -also called stratum basale because it attaches firmly to the basal lamina of the basement membrane -contain progenitor or stem cells = produce the basal cells that mature into all cells of the epithelium -these basal cells tend to cluster and are more frequently found at the bottom of the retes of the epithelium

2. prickle layer or skin = stratum spinosum: -called the “spiny layer” because of histological appearance -tend to shrink from each other and remain connected by desmosomes -several layers thick -connected by bundles of intermediate filaments called tonofilaments -division of cells within this layer increases thickness -melanocytes are common -Langerhans cells also found desmosome gap junction

3. granular or skin = stratum granulosum: -made up of epithelial cells displaced from the prickle -in keratinized epithelium – cell synthesize large quantities of proteins appears granular -the granules = keratohyalin granules (including keratin) – cytoplasm -as keratin is made – cells become thinner and flatter -the plasma membrane thickens and becomes less permeable -the cells then die and dehydrate

4. keratinized layer/superficial layer (skin = stratum corneum): -in the masticatory mucosa - large amounts of keratin are present so the outermost layer = keratinized layer (stratum corneum = skin) -BUT in the lining mucosa – no keratin is made – this layer is called the superficial layer – presence of keratin prevents growth of microorganisms and physical damage -covered in secretions from glands to provide some moisture -keratinized layers – cells do not contain nuclei -pattern of keratinization in these cells = orthokeratinization -a variation in keratinization is seen in the mucosa of parts of the hard palate and much of the gingiva = parakeratinized mucosa -in the skin – parakeratinization is a disease state (e. g. psoriasis) – normal in oral mucosa -the keratinized mucosa of the oral cavity – 20 cell layers thick -can be thicker than the palms and soles!!!!

Keratinized Epithelium Basal layer cuboidal or columnar cells bundles of tonofibrils site of cell division larger ovoid cells large tonofibrils (bundles of tonofilaments) Non-Keratinized Epithelium Prickle layer flattened cells large keratohyaline granules with tonofibrils Granular layer NK = intermediate extremely flattened cells dehydrated loss of organelles and nuclei cells filled with keratin parakeratinization occurs in some tissues Keratinized layer NK = superficial larger ovoid cells smaller more dispersed tonofilamentbundles more numerous filaments prickles are less numerous slightly flattened cells many dispersed tonofilaments glycogen granules not that different from the prickle layer in appearance = stratum intermedium slightly flattened cells with dispersed filaments and glycogen few organelles nuclei persist stratum superficiale

Lamina Propria • highly vascularized tissue • connective tissue with varying amounts of collagen and elastic fibers • papillae can vary in number, height and width depending on region of mucosa

Submucosa -high concentration of blood vessels and nerves in the submucosa -site of the minor salivary glands – in the intestine the submucosa is called the muscularis mucosae -no such thing in oral mucosa - in the OM of the cheeks, lips and part of the hard palate – submucosa layer is made of loose areolar or adipose tissue -in regions such as the gingiva and part of the hard palate – the submucosa is NOT present - the oral mucosa attaches directly to the periosteum of underlying bone = mucoperiosteum

Lining mucosa • includes the buccal, labial, alveolar mucosa, the mucosa of the floor mouth, ventral surface of tongue, soft palate • the interface between the epithelium and lamina propria is relatively smooth with fewer and less pronounced rete ridges and connective tissue papillae (comparable to the dermal papillae of skin) • lamina propria – presence of elastic fibers

This is a section of labial mucosa. The epithelium (B) is nonkeratinized stratified squamous. Examine the uppermost layer (*) carefully and note that these cells still exhibit nuclei. The loose connective tissue of the lamina propria that underlies the epithelium inserts up into this overlying layer in finger-like projections or papillae (A). -the non-keratinized epithelium is very thick -the LP has an extensive vascular supply -the LP have blunt and irregular papillae -the submucosa contains adipose tissue and minor salivary glands & is firmly attached to underlying muscle

The alveolar mucosa lines the alveolar bone of the oral cavity and is nonkeratinized. The connective tissue of the lamina propria (A) is quite dense. Several very low connective tissue papillae are present (B). -very thin nonkeratinized epi. -extensive vascular supply to the LP = redder mucosa than buccal or labial -papillae can be absent sometimes -LP with many elastic fibers, also made up of dense irregular connective tissue -submucosa with minor salivary glands and elastic fibers in a loose areolar connective tissue – gives increased moisture and increase motility

This is the mucosa of the oropharyngeal aspect of the soft palate and is nonkeratinized. It resembles the buccal and labial mucosa; - the connective tissue papillae (A) are of moderate height -thick LP with numerous papillae -LP has a distinct elastic layer for increased mobility

Photomicrograph of lining mucosa from the underside of the tongue. The nonkeratinized epithelium is thin, with only a slight ridge pattern, and is bound to the underlying muscle by a narrow lamina propria. The lower layer on this image is the mucosa that lines the floor of the mouth (under the tongue). It reflects up onto the ventral surface of the tongue above (A). Note the glands (B) and fat cells in the submucosa of the floor of the mouth. The height of the connective tissue papillae in this region is also relatively low. The epithelium is non-keratinized stratified squamous.

Masticatory Mucosa • • • hard palate gingiva exposed to compressive and shear forces during mastication dorsum of the tongue has the same functional role but it is considered as specialized mucosa epithelium is relatively thick and frequently orthokeratinized the gingiva and palate also has parakeratinized very convoluted junction between EP and LP numerous elongated papillae – good mechanical attachment thick LP – dense network of CN fibers in the form of large packed bundles the LP is bound firmly to underlying bone (mucoperiosteum) or indirectly by a fibrous (not a loose, fatty) submucosa

Keratinization of stratified squamous epithelium may occur at sites in the oral cavity where the mucosa is subjected to habitual mechanical stress such as continuous trauma from chewing. Note the typical appearance of the keratinized layer (A). No nuclei are visible in contrast with the parakeratinized variety.

The mucosa covering the hard palate exhibits a distinct keratinized layer - (A). A characteristic feature of keratinized regions in the oral cavity is the presence of relatively high connective tissue papillae (C) projecting into the overlying epithelium. High connective tissue papillae are associated with keratinized epithelium. This form of keratinization in the oral cavity is referred to as orthokeratinized stratified squamous epithelium.

Photomicrograph of the junction (dashed line) between mucosae covering the hard and the soft palate. The difference in thickness and the ridge pattern between keratinized epithelium of the hard palate and nonkeratinized epithelium of the soft palate is apparent. The section has been stained by the van Gieson’s method to demonstrate collagen; the thick dense bundles in the lamina propria of the hard palate appear different from the thinner fibers in the soft palate. Extensive minor salivary glands occur beneath the mucosa. -the hard palate has a thick orthokeratinized epi -overlies a thick LP -submucosa found at the lateral margins of the hard palate -the firm feeling in the medial portion – due to lack of SM + the LP is directly attached to bone – therefore the LP serves as a mucoperiosteum

-attached gingiva that covers the alveolar bone is opaque pink if healthy -stippling can be observed clinically as little depressions on the surface – “orange peel” Parakeratinized epithelium of attached gingiva. Note the connective tissue papillae (A). The overlying epithelium is keratinized There is the absence of a distinctive stratum granulosum and the presence of nuclei (*) in the outermost layers (absent in a stratum corneum).

Alveolar (B)-gingival (A) transition -where masticatory meets lining mucosa -between attached gingiva and alveolar mucosa at a slight indentation called the mucogingival groove (bright pink to paler pink) -keratinized or parakeratinized of gingiva to the thicker nonkeratinized of alveolar -the LP of the gingiva has numerous CN bundles attaching to the periosteum = stippling -the LP of the alveolar is loose connective tissue with numerous elastic fibers and a thicker submucosa

In this section through the gingiva, the space (C) between the dentin of the tooth (A) on the right and the gingiva (B) on the left is normally occupied by enamel which has been lost during tissue processing. Note the high connective tissue papillae (*) that insert into the keratinized epithelium (D) that faces the oral cavity. The mucosa facing the enamel space lacks connective tissue papillae and a keratinized layer. It is called sulcular or crevicular epithelium (E) The sulcus is the shallow groove between the gingiva and tooth. The Dentogingival junction: -where the oral mucosa meets the surface of the tooth -potential weakness in the continuous epithelial lining of the oral cavity A, Diagram of the different types of epithelium: oral (gingival) epithelium (OE), oral sulcular epithelium (OSE), and junctional epithelium (JE). The junctional epithelium is attached to the enamel of the tooth (E) by the internal basal lamina (IBL). Fibers of the periodontal ligament (deep connective tissue) insert into the cementum (C) of the tooth. BL, basal lamina of the gingiva; CT, connective tissue; D, dentin; GC, gingival crest; GS, gingival sulcus. B, Histologic section showing the tissues illustrated in A. Decalcification of the specimen has removed the tooth enamel, leaving an enamel space (ES).

-the walls of the sulcus are lined with an epithelium continuous with the rest of the oral mucosa = oral sulcular epithelium (nonkeratinzed) -the floor of the sulcus is lined with junctional epithelium -derived from the dental epithelium of the tooth germ -smooth connective interface with the epithelium -nonkeratinized -notice lack of connective tissue papillae -cells differ from those of other nonkeratinized oral mucosae – poorly differentiated -cell structure may contribute to increased permeability of this epithelium -the free edge of the sulcus is made of keratinized or parakeratinized epi. -continuous with the OSE at the gingival crest (GC)

The Tongue • • dorsal surface = specialized mucosa similar to masticatory but is highly extensible has unique papillae types and structure mucous membranes are of two parts – divided by the V-shaped sulcus terminalis • anterior 2/3 – body of the tongue • posterior 1/3 – base – contains the lingual tonsils

In this cross-section through the tongue note the absence of a submucosa. Skeletal muscle fibers anchor directly into the lamina propria (A). The overlying epithelium (B) is of the non-keratinizing stratified squamous type.

Histologic sections of three types of lingual papillae. A, Several filiform papillae and a fungiform papilla from the anterior part of the tongue. The epithelium of the filiform papillae is keratinized; that of the fungiform papilla is keratinized thinly or nonkeratinized. The arrowhead points to a taste bud in the epithelium. B, Section through the foliate papilla. The nonkeratinized epithelium covering the papilla contains numerous taste buds (arrowheads) situated laterally. C, Histologic section of taste buds in the epithelium of circumvallate papilla A deep groove runs around the papilla, and the glands of Ebner empty into it. Inset: Enlarged view of a simple taste bud with its barrel-like appearance and the apical pore (arrowhead).

Note the numerous papillae covering the dorsum of the adult tongue. They give the surface a textured appearance. The majority of the tiny projections in this image are filiform papillae (A). Filiform papillae are found over the entire anterior portion of the tongue They are exposed to constant abrasive action during eating, talking, swallowing, etc. This results in their tips becoming protected by a layer of keratin. A buildup of keratin can result in their elongation – has a hairy appearance = hairy tongue This is the histological appearance of filiform papillae. Keratinization (A) occurs on the tips of these papillae. Each papilla has a core of connective tissue (B).

In the center of the field is a fungiform papilla (A). To either side are filiform papillae (B). Fungiform papillae are found on the anterior portion of the tongue They are roughly mushroom-shaped. Their apical surface is not initially keratinized. The surrounding filiform papillae exhibit heavy keratinization (D) of their tips. This layer prevents underlying vasculature in their core from showing through, giving them a more opaque (whitish) appearance on the dorsum of the tongue.

This is a section through three foliate papillae Skeletal muscle fibers (A) extend from the muscular layer below, up into the center of each papilla, where it inserts into the lamina propria of their connective tissue core. They are usually not numerous in humans (can be lost during childhood) Usually found in parallel ridges on the lateral aspect of the tongue Taste buds (B) are also present in the mucosa of their lateral aspects. A taste bud (A). It is composed of two types of cells, neuroepithelial and supporting (sustentacular) cells. The neuroepithelial cells communicate with the free surface of the mucosa by the taste canal (B). The inner and outer openings of the canal are called the inner and outer taste pores. Microvilli ("taste hairs") project from the ends of the neuroepithelial cells into the taste canal. There are from 4 to 20 neuroepithelial cells in each taste bud. These cells are usually located centrally in the structure, surrounded by their supporting or sustentacular cells

This is a dorsal view of a sagittally sectioned tongue from a cadaver. Near the center of the field are two relatively large circular areas (B). These are circumvallate (vallate) papillae. A V-shaped line of circumvallate papillae indicate the approximate site of the boundary between the anterior 2/3's of the tongue (A) and the posterior 1/3 (P). The surface of the posterior 1/3 is much smoother than the anterior 2/3 s. The posterior 1/3 is the site of the lingual tonsils. The anterior 2/3 s is covered with various lingual papillae fungiform (C) and filiform (D).

This is a higher magnification of a circumvallate papilla than seen in the preceding image. The light spherical areas in the epithelium of the walls of the papilla (A) are taste buds. A duct (B) from the underlying glands of von Ebner can be seen opening into the moat-like space (C) around the papilla. Directly below the base of this papilla is a collection of nerve tissue (D).

Mucous glands (A) lie between the lamina propria (B) and the underlying musculature of the posterior 1/3 of the dorsum of the tongue. The number of skeletal muscle cells entering the lamina propria is markedly reduced from that seen in the anterior 2/3 of the tongue. The epithelium (C) covering the dorsum of the posterior 1/3 of the tongue is not as firmly attached as is that of the anterior 2/3 s. The epithelium is classified as non-keratinized stratified squamous. This section through a lingual tonsil reveals a collection of the structural and functional units that compose these organs - lymphoid nodules (A). These structures aggregate around a pit or primary crypt (B) that opens onto the free surface of the mucosa. Typically the surface would be lined by non-keratinizing stratified squamous epithelium that continues down into the crypts. Mucous glands (C) secrete into the bottom of the crypts. The secretions "flush" the crypts of debris to prevent stagnation and the development of infection. The posterior aspect of the tonsil is surrounded by a connective tissue capsule (D).

This image illustrates the junction of the mucous membrane of the oral cavity with the skin of the lip (A). Skin is to the right (B) and is composed of the epidermis (epithelial layer) and the dermis (dense connective tissue layer). Mucosa (C) on the left, is composed of epithelium and lamina propria (dense connective tissue layer). At the mucocutaneous junction (A) the epithelium of the mucosa is continuous with that of the skin and the lamina propria is continuous with the dermis. Deep to the lamina propria, the submucosa is the counterpart to the hypodermis of the integument.

Sagittal section through the lip. The skin covering the external aspect has a thin epidermis and contains hair follicles. Continuous with this is the vermilion zone, which has a thin epithelium overlying an area of extensive vascularity. Between the vermilion zone and the labial mucosa of the oral cavity is the intermediate zone. Minor salivary glands occur beneath the labial mucosa, and the extensive muscular tissue represents part of the orbicularis oris.

The Mucocutaneous Junction -transitional region from lips to the labial mucosa -few sebaceous glands are present only at this margin -thin keratinized epithelium -long connective papillae with capillary loops (brings blood close to the surface) -between the vermillion zone (lips) and the labial mucosa is an intermediate zone of parakeratinized epithelium