oral mucosa

د.سحرغانم القزاز Oral Mucous Membrane Lec.4 ( Oral Mucosa)
Definition of the oral mucosa:
is the mucous membrane lining the inside of the oral cavity and consists of stratified squamous epithelium termed oral epithelium and an underlying connective tissue termed lamina propria.
The oral cavity has sometimes been described as a mirror that reflects the health of the individual. Changes indicative of disease are seen as alterations in the oral mucosa lining the mouth, which can reveal systemic conditions, such as diabetes or vitamin deficiency, or the local effects of chronic tobacco or alcohol use.
Functions of the oral mucosa:
- Protection – barrier for mechanical forces during chewing and microb insults.
- Sensation – temperature, touch, pain, taste, thirst, reflexes (swallowing, gagging, salivating).
certain receptors in oral mucosa probably respond to the taste of water and signal the satisfaction of thirst.
- Secretion – the major secretion associated with the oral mucosa is saliva.
Types of Oral Mucosa:
It can be divided into three main categories based on function and histology:
1.Masticatory mucosa: (25%) in contact with food during mastication, the masticatory mucosa is firmly attached to underlying tissue and keratinized stratified squamous epithelium, found on the dorsum of the tongue, hard palate and attached gingiva.
2.Lining mucosa: (60%) covers floor of mouth, ventral surface of tongue, alveolar mucosa, cheeks, lips, soft palate. The lining mucosa loosely attached to underlying tissue and non keratinized stratified squamous epithelium.
3.Specialized mucosa: (15%) specifically in the regions of the taste buds on lingual papillae on the dorsal surface of the tongue that contains nerve endings for general sensory reception and taste perception.
Histology of Oral Mucosa:
Oral Mucosa is composed of:
1-Oral Epithelium:
Types of oral epithelium:
A. Ortho keratinized stratified squamous epithelium : no nucleus in keratin layer.
B. Para keratinized stratified squamous epithelium : has nucleus in keratin layer.
C. Non keratinized stratified squamous epithelium .


A. Ortho keratinized stratified squamous epithelium :

It composed from 4cell layers which are:

Superficial layers of stratified squamous epithelium that include from deepest to most superficial:1: Stratum basale(basal layer):
is layer of cuboidal or columnar cells have a capacity to divides and proliferates, so the divided cells can travels to surface replacing the desquamating surface cells. 2: Stratum spinosum(prickle layer):
Composed several rows of layer elliptical or spherical cells also they known as the prickle cell layer these cells appear frequently shrink away from each other remaining in contact only at points known as inter cellular bridges or desmosomes. They are active in protein synthesis, however, some mitotic figures may be seen in spinous cells just beyond the basal layer. therefore the stratum basale and the first layers of stratum spinosum are known as agerminative layer because these cells give rise to new epithelial cells.
3.Stratum granulosum(granular layer):
These are flatter and wider cells ,the cell are larger than spionous cells. The stratum granulosum contain basiophilic keratohylain granules in their cytoplasm , Keratohyaline granules help to form the matrix of the keratin fibres found in the superficial layer . The nuclei show signs of degeneration and pyknosis.

4: Stratum cornium

other name(cornified layer, horny layer, keratinized layer) : the cells are larger and flatter than granular layer ,the nuclei and other cytoplasmic organelles such as ribosome and mitochondria have disappeared. The layer is acidophilic (red staning with hematoxylin and eosin).
B. Para keratinized epithelium: the cell layer similar to keratinized epithelium, that is composed of 4 layers, but it differ from that by the remain of the pyknotic nuclei at the surface layer.
C. Non keratinized squamous epithelium:
*Stratum basale : basal cell layer comprised of cuboidal cells.
Progenitor cells divide and provide new cells via mitotic division to replace dead surface cells which are shed.
*Stratum spinosum/intermedium : cells are oval, represent bulk of epithelium.
*Stratum superficial : cells are flat, contain small oval nuclei that are continuously shed.

2-Connective tissue( lamina propria):

connective tissue component is called lamina propria
epithelium and connective tissue form an interface that form corrugated papillae. papillae of connective tissue protrude toward epithelium carrying blood vessles and nerves. Epithelium does not contain blood vessels. Epithelium in turn is formed into ridges that protruded toward the lamina propria.
Interface is irregular, downward projections of epithelium called rete ridges or pegs(epithelial ridges), upward projections of CT called CT papillae.
The lamina propria is a fibrous connective tissue layer that consists of a network of type I and III collagen and elastin fibers in some regions. The main cells of the lamina propria are the fibroblasts, which are responsible for the production of the fibers as well as the extracellular matrix.


The lamina propria, like all forms of connective tissue proper, has two layers:
- Papillary layer.
- Reticular(dense) layer.
The papillary layer: is the more superficial layer of the lamina propria. It consists of loose connective tissue within the connective tissue papillae, along with blood vessels and nerve tissue.
The reticular layer: is the deeper layer of the lamina propria. It consists of dense connective tissue with a large amount of fibers. Between the papillary layer and the deeper layers of the lamina propria is a capillary plexus, which provides nutrition for the all layers of the mucosa and sends capillaries into the connective tissue papillae.The lamina propria is attached to the periosteum of the alveolar bone or may overlay the sub mucosa.
Cells present in Lamina Propria (non keratiocyte cells)
Fibroblasts , Histiocyte, Macrophage , Mast cell, Neutrophil, Lymphocyte
Plasma cell , Endothelial cell.
3- Basal lamina(basement membrane):
Interface between epithelium and CT within the CT comprised of structure less layer called basement membrane. is evident at the light microscope .
(basal lamina) is evident at the electron microscope level and is epithelial origin. Under electron microscope this structure seen composed from two layers which are :
A .Lamina lucida which present on epithelial side.
B. Lamina densa which present on the connective tissue side.
The basal lamina act as a permeable barrier and act as anchoring structure between epithelium and connective tissue of oral mucous membrane.
4-Sub mucosa:
may or may not be present deep to the dense layer of the lamina propria , depending on the region of the oral cavity. If present, the sub mucosa usually contains loose connective tissue and may also contain vascular and neural components and adipose connective tissue or salivary glands, as well as overlying bone or muscle within the oral cavity.
1.Masticatory mucosa:
The gingiva and hard palate are covered by masticatory mucosa.
Hard Palate
- Orthokeratinized (parakeratinized in some areas) showing ridges (rugae)
- Lamina propria shows long papillae with thick, dense CT
- Submucosa is mucoperiosteum with dense collagenous CT attaching directly to periosteum. Contains fat and salivary glands


2.Lining Mucosa (Non keratinized squamous epithelium):
Lip Histology
The inner oral surface of the lips is lined with moist surface, stratified squamous non-keratinized epithelium .and is associated with small round sero-mucous glands of the lamina propria. these glands are part of the minor salivary glands
Found throughout the oral cavity .beneath the lamina propria is the sub mucosa
In which fibers of the orbicularis oris muscle are located.
non-keratinizing mucosa of the lips is distinguished by a red border known as the
vermillion border.this area is at the junction between the oral mucosa and the the skin of the lips, becoming modified into keratinized epithelium,which is differ from skin or mucosa.
Threre are three reasons that the vermillion border is red including the following: the epithelium is thin, this epithelium contains eleidin(transparent substance present in stratum lucidum of skin epithelium)and the blood vessels are near the surface of the papillary layer, reveling the red blood cells color.
also observable in the skin of the lips are hair follicles and their associated sebaceous glands, sebaceous glands can be seen at the angles of the mouth .They are not associated with hair follicles. these glands are known as Fordyce ’s spots.

Salivary glands are lacking in the vermillion zone, therefore, the lips must be continuously moistened(by the tongue) to prevent drying out.

Soft Palate

- Submucosa contains salivary glands and muscle of soft palate.

Cheeks

- Similar to lips and soft palate – non keratinized, lamina propria, and submucosa
- Submucosa of cheeks has fat cells and lobules of minor salivary glands and muscle fibers.
Ventral Tongue
- Non keratinized, The lining mucosa here contains both lamina propria and submucosa The submucosa merges with the muscle bundles of the ventral surface of the tongue.


Floor of the mouth
- Nonkeratinized, lamina propria, submucosa.
- Epithelium loosely attached to lamina propria.
- No muscle, lots of salivary glands.
3.Specialized mucosa:
this specifically in the regions of the taste buds on lingual papillae on the dorsal surface of the tongue that that contains nerve endings for general sensory reception and taste perception. The connective tissue binds the epithelium to the underlying skeletal muscle. The epithelium is modified, keratinized, stratified covered with papillae.
Taste Buds
- Neuroepithelial structures – epithelial cells closely associated with clib-shaped sensory nerve endings. Taste buds contain the receptors for taste. They are located around the small structures on the upper surface of the tongue, soft palate, upper esophagus and epiglottis, which are called papillae.
o Nerves arise from chorda tympani (anterior tongue), glossopharyngeal (posterior tongue), vagus (epiglottis and larynx) and lie among taste cells
- Each bud has 10-14 cells, majority are taste with elongated microvilli projecting into taste pore.
- Tastes:
Sweet – anterior, Salt – lateral anterior , Sour – lateral , Bitter – circumvallate papilla.

The different papillae found on the dorsal surface of the tongue are:

- Filiform papilla –majority of papillae, covers anterior part of tongue
o Appear as slender, keratinized projections (2-3mm) of surface epithelial cells
o Facilitate mastication by compressing and breaking food when tongue apposed to hard palate.
o Directed towards throat, assist in movement of food towards throat
o No taste buds.
- Fungiform papilla – interspersed between filiform papilla
o These are present mostly at the dorsal surface of the tongue, as well as at the sides.
o Smooth, round, appear red because of highly vascular CT core
o Seen through thin, non keratinized epithelium
o Taste buds seen within epithelium


- Foliate papilla – present on lateral margins of posterior tongue, appear leaf-like
o Consist of 4-11 parallel ridges that alternate with deep grooves in mucosa
o A few taste buds present on epithelium
o Contain serous glands underlying taste buds which cleanse grooves

- Circumvallate papilla – on V-shaped sulcus

o 10-14 in number between base and body of tongue
o Large (3mm diameter) with deep surrounding groove
o Ducts of von Ebner glands (serous salivary glands) open into grooves
o Taste buds seen lining walls of papillae.

Odland bodies or lamellar granules found in Stratum spinosum and Stratum granulosum of skin forming an important barrier to permeability.