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LLU: Medicine: Anatomy: Histology Mentor: Oral Histology
Histology Mentor
ORAL HISTOLOGY
A. Oral mucosa - stratified squamous non-keratinized epithelium resting on an irregular c.t. lamina propria. Extensive c.t. papillae and a stratum corneum(parakearatin retains pyknotic nuclei), as well as a granular layer containing a few keratohyalin granules, are found where the mucosa is attached to the bone (gingiva and hard palate). Acini of minor salivary glands (mixed mucous) are found in the deep, more loosely arranged portion of the c.t., sometimes called the submucosa. The concentration of IgA in the secretions of minor salivary glands is 4X that of the parotid. As much as 30% of the IgA in saliva may come from this source (Science 190:1206). The mucosa is supported by skeletal muscle in the cheek, soft palate, and pharynx.
Lip
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1. Vermillion border (Stratified squamous keratinized epithelium) 2. Keratin 3. Skeletal muscle 4. Sebaceous gland around hair follicle 5. Minor salivary gland 6. Lamina propria (Irregular c.t.) |
2. Soft palate and uvula
a. Oral surface - stratified squamous non-keratinized; mucous glands in submucosa surrounded by fat
b. Skeletal muscle support
c. Nasopharyngeal surface - pseudostratified ciliated columnar (cilia beat toward oral pharynx) and often, due to metaplasia, stratified columnar to squamous epithelium. Small mixed glands are in lamina propria and diffuse lymphoid cells are more numerous than in oral mucosa. No true submucosa.
3. Pharynx - initiates the swallowing reflex. It is lined by stratified squamous non-keratinized epithelium, resting on a fibroelastic lamina propria containing mucous glands. A layer of elastic fibers is net to the muscle. Its muscular wall consists of two layers of skeletal muscle; the constrictor pharyngeus (external circular), and the stylopharyngeus and palatopharyngeus muscles (an internal longitudinal layer).
4. Floor of Mouth - has a thin stratified squamous nonkeratinized epithelium with a very vascular lamina propria. Some drugs can be administered by absorption here.
B. Tongue - supported by skeletal muscle oriented in three planes. The dorsal aspect of the tongue presents a specialized mucosa. This surface is covered by a mixture of filiform and fungiform papillae, while circumvallate papillae are found along the "V" shaped sulcus terminalis. Pure serous glands open into the "moat" surrounding the circumvallate papillae. Lingual tonsils are behind the sulcus terminalis and pure mucous glands open into their crypts. the under surface of the tongue is similar to the floor of the mouth.
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1. Epithelium, stratified squamous-pseudo-keratinized 2. Filiform papillae 3. Fungiform papilla 4. C.t. cores of papillae 5. Bundles of skeletal muscle oriented in three different planes |
1. Taste buds - lightly stained ovoid structures in the epithelium of circumvallate and fungiform papillae as well as a few in the soft palate and pharynx. Spindle-shaped sensory cells extend microvillus processes through a small opening (pore) to the surface. Afferent (sensory) nerve fibers terminate at the base of these cells. Small basal cells proliferate to replace the supporting and sensory cells.
C. Teeth - Each tooth has a crown that consists of enamel and its underlying dentin overlying the pulp chamber. Blood vessels and nerves enter the pulp at the apex and the tooth is held in place by the periodontium. The periodontium consists of the alvolar bone that forms the tooth socket, a connective tissue periodontal ligament that anchors the tooth to the bone on one side, and cementum on the other and the gingiva. The gingiva protects the deeper structures of the periodontium from the oral environment. It is a mucosa whose lamina propria attaches to the periosteum of the bone. At the bottom of the gingival sulcus (3 mm deep) its epithelium (stratified squamous) attaches, by means of hemidesmosomes, to a basal lamina-like cuticle on the surface of the tooth. Oxytalan fibers are found among the type 1 collagen fibers of the periodontal ligament. Myofibroblasts in the periodontal ligament probably aid in tooth eruption. Break down of the periodontal ligament in vitamin C deficiency is indicative of the high turnover of its fibrillar components.
1. Structure
a. Enamel - hardest substance in the body is only 3% organic matrix, that is a type of keratin. It is made only during tooth development by ameloblasts, that form a covering of epithelium on the crown of the developing tooth. These very tall, highly polarized columnar cells secrete the enamel matrix and influence mineralization. The ameloblasts die upon completion of the enamel; therefore, enamel is acellular.
b. Dentin - more mineralized than bone, it is 80% mineral. It is formed very slowly but continuously throughout life by odontoblasts that line the pulp chamber. Dentinal tubules, that run from the dentino-enamel and cemento-dentinal junctions to the pulp cavity, contain processes of odontoblasts. Tight junctions between odontoblasts help maintain a continuous epithelial layer between pulp and dentin. Odontoblasts: 1) form predentin, that is about 90% collagen; 2) influence mineralization; 3) maintain a circulation of fluid in the dentinal tubules and out through the enamel; and 4) act as sensory receptors.
c. Cementum - a bone-like material covering the root and providing an anchor point for the collagen fibers (Sharpey's) of the periodontal ligament. Cementum is thickest around the apex of the tooth and, in that location, contains cementocytes in lacunae This is called cellular cementum. Elsewhere the thin layer covering the root is called acellular cementum.
a. Dental lamina - a ridge of epithelium following the outline of the jaw. It develops from the ectoderm lining of the mouth.
b. Tooth germs - bud-like thickenings at intervals along the dental lamina. They induce the condensation of neural crest derived mesenchyme (ectomesenchyme) to form the dental papilla over which the ectodermally derived tooth germ differentiates to form the enamel organ.
c. Enamel organ - expands and differentiates into three regions; 1)the outer enamel epithelium, 2)the inner enamel epithelium and 3)between those two the stellate reticulum, a network of epithelial cells. The enamel knot is a condensate of stellate reticulum over the site of the presumptive cusp. Its cells produce in an orchestrated fashion a variety of growth factors and signaling molecules that determine the shape of the crown.
d. Inner enamel epithelium - ameloblasts differentiate in the enamel organ along the surface of contact with the dental papilla. They induce the formation of odontoblasts in the adjacent papilla. When the odontoblasts begin secreting the dentinal matrix, the ameloblasts are induced to produce enamel matrix. Therefore, enamel is laid down from the inside out, but dentin from the outside in. In the fully formed tooth many Type I collagen fibrils are found crossing from the dentin into the enamel. J. Histochem Cytochem 41:381, 1993
Successive stages of development are named:
1) Bud,
2)Cap, enamel organ forms a cap over the dental papilla,
3)Bell, enamel organ is fully formed and takes the shape of a bell,
4)Apposition, deposition of enamel on the dentin has begun
5)Eruption, tooth has emerged through the gingiva
A. Minor - small glands in the mucosa and submucosa of the oral mucosa, usually pure mucous or mixed mucous but may be serous, as are the gustatory glands under the circumvallate papillae of the tongue.
B. Major - parotid, submandibular and sublingual. The mucous secretory units are tubular, serous units are acinar. The major salivary glands have a branched duct system with small intercalated ducts connecting the secretory units to intralobular, striated ducts, that in turn open into the interlobular ducts. The serous secretions contain enzymes (salivary amylase, lipase, lysozyme and lactoferrin.) and secretory immunoglobulin. The striated ducts, that have many basal infoldings and interdigitations with radially arranged mitochondria, modify the electrolyte composition by adding potassium, removing most of the sodium and reducing the osmolarity. Some hormones may be produced by these glands.
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Parotid Gland 1. Serous acini 2. C.T. septa separating gland into lobules 3. Intralobular ducts 4. Interlobular ducts |
1. Parotid - almost pure serous, obvious striated ducts. Fat cells in interlobular tissue
2. Submandibular - mixed serous, numerous striated ducts
3. Sublingual - about 60% mucous without significant striated ducts
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