Oral and nasal cavities



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ORAL AND NASAL CAVITIES

Diane Bick Ph.D., FAHA
Reading: Gartner and Hiatt, pp267-287, 247, 248, 252, 254-255; Gartner, Hiatt, Strum, 228-230, 244-247
Learning Objectives:

  • Know the components of the oral and nasal cavities and describe the epithelia lining each.

  • Describe and differentiate the different papillae on the human tongue.

  • Recognize the distinctive musculature of the tongue.

  • Know the different cell types within a taste bud and their different roles in the taste sensation.

  • Understand the structure, function and development of the different histological components of the tooth.

  • Describe the histological composition of the olfactory epithelium and describe the roles of the different cell types.

Key Words: Papillae, taste bud, olfactory epithelium, respiratory epithelium, dentine, enamel, cementum.
ORAL CAVITY.

  • Responsible for the ingestion and preliminary processing of food.

  • Formed by the lips, cheek, hard and soft palate and the floor of the mouth.

  • The walls of this cavity are lined with a stratified squamous epithelium.


1. LIPS

  • External aspect: thin skin with keratin, hairs, sebaceous glands and eccrine sweat ducts.

  • Transitions to the moist, inner surface at the transitional or vermilion zone.

  • Transitional zone has no sweat ducts or hair follicles and is the site of the transition from a keratinized epithelium to a non-keratinized stratified squamous epithelium.

  • Underlying rich capillary network and the presence of kerato-hyaline, which makes the epithelium more transparent, causes the deep red colour.

  • The submucosa of the lips contains numerous small mucus and seromucus glands.

  • The central core of the lips is composed of striated muscle embedded in elastic fibro-connective tissue.


2. TONGUE

  • A freely moving structure attached to the floor of the pharynx.

  • A mass of striated muscle covered by a mucous membrane.

  • The muscle fibers of the tongue cross one another in three planes and four layers; they are grouped together in bundles separated by connective tissue, serous, mucous and seromucus glands.

  • The ventral surface of the tongue is covered by a thin, non-keratinizing stratified squamous epithelium continuous with that of the floor of the mouth.

  • The dorsal surface however is subject to more stress and is covered by a thick keratinizing stratified squamous epithelium.



Dorsal Tongue

  • Divided into the anterior two-thirds and the posterior third, these two regions arise from different embryonic origins.

  • They meet at a V-shaped boundary.

  • The posterior portion contains low dome-shaped elevations of lymphoid tissue, the lingual tonsils. The overlying stratified squamous, non-keratinizing epithelium extends down into the lymphoid tissue as deep pits or crypts. Mucus glands secrete into these crypts and keep them free of debris.

  • The surface epithelium of the anterior zone of the dorsal surface of the tongue is raised in a series of elevations called papillae. There are three main types of papillae; circumvallate, filiform and fungiform.


a. Circumvallate Papillae


  • These are the largest in size and smallest in number.

  • They appear as flattened domes forming a V-shaped row at the border between the anterior and posterior zones.

  • These structures are surrounded by a deep groove with numerous taste buds along its lateral, stratified, non-keratinizing, squamous epithelial wall.

  • Serous glands of von Ebner open through ducts at the base of the groove.

  • The glands of von Ebner also secrete a lipase that probably prevents the formation of a hydrophobic layer over the taste buds, which would hinder their function.


b. Filiform Papillae


  • Most numerous and have an elongated, conical, appearance.

  • Present over the entire dorsal surface of the tongue.

  • The epithelia of filiform papillae contain no taste buds and are frequently partly keratinized (parakeratosis).


c. Fungiform Papillae

  • Mushroom-shaped papillae scattered randomly across the dorsal surface.

  • A connective tissue core with fingers of connective tissue projecting into the surface epithelium. The surface epithelium contains taste buds.


d
Fungiform Papilla
. Foliate Papillae

  • Poorly developed in man but can be found in two or more parallel ridges on the dorsolateral surface of the tongue.

  • Taste buds in the epithelia degenerate at an early age. Serous glands of von Ebner are also associated with this papilla.

Taste Buds


  • Barrel-like sensory structures embedded in the stratified squamous epithelium

  • Mainly associated with papillae or covering the epiglottis.

  • The sensory and supportive cells surround a small central cavity that opens on to the surface at a tiny taste pore.

  • Each taste bud contains three main cell types:

    1. Sustentacular (supportive); Columnar cells with microvilli and numerous secretory granules in their apical aspect.

    2. Gustatory (sensory); Spindle shaped cells with synaptic vesicles near their basal surface. These cells are closely associated with small afferent nerve fibers. The luminal surfaces of the cells open into a small gap in the epithelium, the taste pore. Each cell has microvilli.

    3. Basal; These are the cells from which other cell types are derived.



3. PHARYNX

      • Transitional space between the oral cavity and the respiratory and digestive systems.

      • Forms a communication between the nasal region and the larynx.

      • The pharynx is lined by a stratified, squamous epithelium except in those regions of the respiratory region that are not subject to abrasion. In these regions the epithelium is typically respiratory (ciliated, pseudostratified columnar).

      • The pharynx contains multiple confluent lymphoid nodules, the pharyngeal tonsils.T

      • The pharyngeal mucosa contains many small mucous glands in fibro-elastic connective tissue. The connective tissue is surrounded by the striated muscle of the pharyngeal muscles.

4. HARD PALATE

  • This structure is covered by a keratinizing stratified squamous epithelium with a prominent rete ridge system and a submucosa rich in mucous glands and adipose tissue.

5. SOFT PALATE

  • The oral surface of the soft palate is covered by with a non- keratinizing stratified squamous epithelium which extends to its posterior edge where there is a transition to a ciliated, pseudostratified columnar epithelium.

  • The oral aspect contains many small mucous glands in its submucosa.

6. CHEEKS

  • Lined by a thick non- keratinizing stratified squamous epithelium whose cells are often rich in glycogen.

  • Areas of chronic friction can become keratinized.

  • The submucosa contains many salivary glands (buccal glands) and occasional sebaceous glands.

7. TEETH

  • Responsible for the fragmentation of large food masses.

  • Teeth are hard, heavily mineralized structures embedded in the raised alveolar ridges of the maxilla and the mandible.

  • In the adult human there are 32 permanent teeth which are preceded by 20 deciduous teeth.

  • Each tooth can be divided into two anatomical components; the crown and the root. The junction between these components is called the neck.

  • The mature tooth has 5 components: the central pulp cavity, dentine, enamel, cementum and peridontal ligament.


A. Pulp


  • Pulp is the soft central core of the tooth.

  • It consists of loose connective tissue whose main components are odontoblasts (at its perimeter), fibroblasts, collagen and a ground substance containing glycosaminoglycans.

  • Pulp is highly innervated and vascularized. Blood vessels and myelinated nerve enter the apical foramen and divide into numerous branches.

  • The outer surface of the pulp cavity is lined by odontoblasts that continually produce dentine. As dentine is progressively laid down the pulp cavity diminishes in size.


B. Dentine


  • Dentine is a calcified tissue composed of 70-80% calcium salts in the form of hydroxyapatite and 20-30% organic tissue.

  • The organic material is composed of the fine cytoplasmic processes of odontoblasts, type I collagen fibres and glycosaminoglycans.

  • Dentine is initially laid down as a glycosaminoglycan matrix in which collagen fibers are linearly arranged. This non-mineralized predentine is synthesized by odontoblasts lining the outer surface of the pulp cavity.

  • Odontoblasts have slender, branched, cytoplasmic projections that penetrate perpendicularly the width of the dentine (Tomes Fibers). These processes become longer as the dentine becomes thicker forming small canals or dentinal tubules.

  • Mineralization of predentine begins when membrane-limited vesicles appear which contain fine crystals of hydroxyapatite. These serve as nucleation sites for further mineral deposits.

C. Enamel


  • Enamel is the hardest component of the human body and the richest in calcium.

  • It is composed almost entirely of the mineral hydroxyapatite arranged in tightly packed hexagonal enamel rods. Each enamel rod extends through the full thickness of the enamel.

  • Enamel is formed during tooth development by the ameloblasts, which degenerate when the tooth erupts, so enamel cannot be replaced.

  • A single process of the ameloblast (Tomes process) forms each rod.

D. Cementum


  • Cementum is a calcified, bone-like tissue containing collagen.

  • This tissue covers the dentin of the root.

  • It does not contain Haversian systems or blood vessels.

  • It is thicker in the apical region of the root where there are cementocytes.

  • Cementocytes resemble osteocytes and are encased in lacunae that communicate through canaliculi.

  • Cementocytes can become activated to produce more cementum when required.

  • The primary function of cementum is to provide for the attachment of collagen fibers of the peridontal ligament.

  • Those fibers that extend from the peridontal ligament into the cementum are called Sharpey’s fibers.


E. Peridontal Ligament


  • This is a special dense connective tissue whose fibers penetrate the cementum and binds it to the bony walls of its socket.

  • It serves as the periosteum of the alveolar bone.

  • The fibers of the peridontal ligament are arranged to support the pressures produced during mastication.

  • Collagen of this ligament turns over very rapidly.


GINGIVA

  • This is a mucous membrane firmly bound to the periosteum of the maxillary and mandibular bones.

  • It is composed of a stratified squamous epithelium bound to the tooth enamel by means of a cuticle that resembles a thick basal lamina.

  • Epithelial cells are attached to this cuticle by means of hemidesmosomes.


NASAL CAVITY (Fossae)

  • Two cavernous chambers lie within the skull and are separated the median nasal septum. Extending from both lateral walls of the septum are three curved plates of bone covered by a mucous membrane. These are the superior, middle and inferior conchae.

  • The conchae serve to increase the epithelial surface area, allow the trapping of particulate matter by mucous and increase the humidification and warming of incoming air.

  • The inferior and middle conchae are covered by a respiratory epithelium (ciliated, pseudostratified columnar).

  • A specialized olfactory epithelium covers the superior conchae. This chemoreceptive epithelium extends laterally over the superior conchae and medially over the superior portion of the nasal septum.

  • It is composed of a tall pseudostratified epithelium without goblet cells and formed by three cell types.

    1. Olfactory (sensory) cells; Modified bipolar neurons, their dendrites reach the free surface of the olfactory area. Their unmyelinated axons extend from the basal portion of the cells through the lamina propria and aggregate as small nerves directed toward the CNS. The bulbous tip of the dendrite bears 6-20 immotile, olfactory cilia, which lie flat above the exposed surface.

    2. ii) Sustentacular (supporting) cells; columnar cells with microvilli. These cells contain a lipofuscin like pigment, which imparts a characteristic yellow colour to the olfactory areas.

    3. iii) Basal cells; Small round cells thought to give rise to olfactory and sustentacular cells.

  • The connective tissue under the olfactory epithelium contains Bowman’s glands.

  • These are branched glands that empty their secretions via ducts onto the olfactory surface.

  • T

    Olfactory mucosa with 3 cell types

    he connective tissue contains numerous unmyelinated olfactory nerves, blood vessels and numerous lymphatic tissues.

Within the lamina propria of the conchae are large venous plexuses known as swell bodies.

  • These alternatively become engorged with blood every 20-30 minutes and cause a decrease in air flow thus decreasing desiccation of the respiratory epithelium.

  • Allergic reactions and inflammation can cause abnormal engorgement of the swell bodies and hence restrict air flow.


ORAL AND NASAL CAVITY LABORATORY

Slide 64, Monkey Tongue

1. Identify the following types of epithelium: stratified squamous, nonkeratinizing and stratified squamous keratinizing. How can one distinguish the dorsal and the lateral surfaces of the tongue?

2. Identify 3 types of papillae: Filiform (most numerous, conical projections with the point directed posteriorly). Fungiform (mushroom shaped, scattered throughout the filiform). Circumvallate (largest, surrounded by deep moat or trench, numerous taste buds on lateral surface)

3. Identify serous glands of von Ebner at base of circumvallate papillae.

4. Identify taste buds in lateral surface of circumvallate papillae. Find taste pore. Identify supportive and sensory cells.

5. Identify the arrangement of the skeletal muscle fibers and find the different glands present in the tongue.


Slide 65, Nasal Cavity, SEE DEMO SLIDE AT FRONT OF LAB

Identify:

1. Bone

2. Respiratory epithelium with goblet cells, ciliated pseudostratified columnar cells.



3. The thick olfactory epithelium. How many cell types in this epithelium? How do the sensory cells of taste buds and olfactory epithelia differ?

4. Note the extensive vascularization of this tissue and the presence of many nerve bundles and lymph vessels.



Tooth #92. If you don’t have one, see the Demonstration Slide at the front of the lab

1. Identify root, crown and neck.

2. Identify:

Enamel. Where are the cells that form this material in the mature tooth?

Odontoblasts.

Dentine and dentinal tubules. What cells form these tubules? How does dentine differ from predentin.



Cementum and cementocytes

Apical foramen.


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