Structure and function of oral mucosa

Question 1

What are the borders of the oral mucosa?

Answer 1

Anteriorly at the vermillion border of the lips.

Posteriorly, ends at the anterior pillar of fauces (palatoglossus fold).

Question 2

What two mucosa does the oral mucosa have features of?

Answer 2

Skin and gut

Question 3

What part of the mouth is included in the mucosa?

Answer 3

• Upper and lower labial mucosa (lips)
• Upper and lower labial sulcus (inside lips)
• Free and attached gingiva
• Buccal sulcus
• Buccal mucosa
• Hard and soft palate
• Ventral surface of the tongue
• Floor of the mouth

Question 4

What are the two things that mucosa includes?

Answer 4

Epithelium and lamina propria

Question 5

In the gut, what is the boundary between the mucosa and submucosa called?

Answer 5

The muscularis mucosa.

Question 6

Do we know where the boundaries are in the oral cavity between mucosa and submucosa?

Answer 6

No, there is no muscularis mucosa layer.

general rule is that fat and skeletal muscle indicates mucosa

Question 7

What are downwards projections of the epithelium called?

What projects upwards from the lamina propriety?

Answer 7

Rete processors (pegs)

Connective tissue papillae

Question 8

What are the 3 types of mucosa and state what is included in them?

Answer 8

1. Masticatory mucosa (hard palate and gingiva)
2. Lining mucosa (covers the majority of the oral cavity including the buccal mucosa and sulcus, labial mucosa, ventral tongue and floor of mouth and the soft palate.
3. Specialised mucosa = covers the dorsal aspect of the tongue anterior 2/3 and parts of the lateral margin of the tongue

Question 9

Explain the difference in epithelium thickness at different sites

Answer 9

Thickest in the buccal mucosa but in rete processors are longest in the hard palate.

In floor of mouth, the epithelium is thin and lacks any rete processors. Salivary glands are in the floor of the mouth so the thickness of the lamia propria is very thin.
Lamina propria is thickest in the hard palate forming a continuum with the underlying periosteum.

Question 10

What type of epithelium covers all of the mucosa?

Answer 10

Stratified squamous

Question 11

What type of mucosa has the longest rete processors and why?

Answer 11

Masticatory mucosa to form a larger surface contact with the underlying lamina propria.
Makes this mucosa more equipped to withstand shear forces.

Question 12

What type of mucosa has no submucosa layer?

Answer 12

Masticatory mucosa (lamina propria forms a continuim with the periosteum).

Question 13

Why is trying to raise a mucosa flap on gingiva or hard palate difficult?

Answer 13

As the attachment of the mucosa to the bone is strong in masticatory mucosa. No submucosa layer here means that we can call it the mucoperiostium with taking about masticatory mucosa.

Question 14

Give some details on stratified squamous epithelium?

Answer 14

Self-regenerating stratified squamous keratinising epithelium.
Responsible for the resistant properties of skin.
Principal cell type = keratinocyte.
Organised into clearly recognisable layers.

Question 15

What are the layers found in masticatory mucosa?

Answer 15

(surface inwards)
Keratinised layer 
Stratum granulosum
Stratum spinosum (prickle cell layer)
Basal layer

Question 16

Masticatory mucosa:
Explain how proliferation occurs within the layers
(what cells are there)

Answer 16

Proliferation of the stratified squamous cells occurs in the basal layer and immediate supra basal zones, maturation occurs from prickle cell layer upwards towards surface.

Basal compartment composes both stem cells and transit amplifying cells. A stem cell divides to form these two cells. The amplifying cells matures up the layers of the epithelium.

Question 17

Where should mitotic figures be found in masticatory mucosa?

Answer 17

The basal layer

Question 18

Give details on the basal layer in masticatory mucosa

Answer 18

Basal layer should be short cubiodal in appearance. The nuclei stay more dark. Composes of a single layer of cells usually.
Basal cells are attached to the underlying lamina propria at the basal lamina.
The basal lamina cannot be seen here. Need electron microscope.

Basal cells attach to the basal lamina via hemidesmosomes condensed at the basal cell membrane.
The hemidesmosomes concentrate the intermediate filaments, some of which transverse the cell membrane to attach to the basal lamina.
The basal lamina under electron microscope shows a lamina lucisa and a lamina densa.
There are anchoring fibres of collagen under this which loop to the collagen fibrils of the lamina propria.

Question 19

Where are the proteins in the basal lamina manufactured?

Which protein has a clinical relevance?

Answer 19

Manufactured by the basal epithelial cells.

One of which proteins is the bullous pemphigoid antigen which helps anchors the basal call to the underlying basal lamina. This is important clinically as shown below.

Question 20

What does mucus membrane pemiphigoid?

Answer 20

An auto-immune condition.

This is where the patient immune cells manufacture antibodies against the bullous pemphigoid antigen which weakens the adhesion between the epithelium with the lamina propria.
Get a split between epithelium and lamina propria at the junction between the basal cells and the underlying lamina propria through the basement membrane region.

These splits cause the formation of blisters and bleeding.

Question 21

Explain the composition of the stratum spinosum

Answer 21

The cells of the prickle cell layer are larger than the basal cells, they have larger nuclei but more pale staining, the nucleoli also start to appear at the top of the prickle cell layer.

The prickles (intercellular bridges) are a perperation artefact when making the slides. The cells sink away from each other but the intercellular bridges (representing desmosomes) stay intact to give the intra cellular bridges.

The prickle cell is usually the largest layer of the epithelium.

Question 22

What is pemphigus?

Answer 22

Auto-immune disease that causes blisters.

Patients develop antibodies to the demoglein protein as this causes breakdown in the desmosomes resulting in breakdown between prickle cells.

Gaps appear in the prickle cell layer resulting in a blister.

Question 23

Give details on the granular layer of the masticatory epithelium

Answer 23

The granules are basophilic within the cytoplasms of the cell layer.

Cells become flattened, the nuclei get enlarged and elongate and they also tend to lose a number of the nuclei and other organelles.

The granules are keratohyalin granules. They contain the precursors to a protein called filaggrin.

Question 24

Give details on the cornified layer of the masticatory epithelium

Answer 24

The outer layer.
It is a bright red colour, cells are unrecognisable by organelles as these have been lost.
Tightly packed appearance of cells.

Question 25

Explain the difference between para-keratinised and ortho-keratinsied

Answer 25

Nuclei preserved at the surface is para-keratinisation.

The lack of nuclei are present here in the superficial zone. This is ortho-keratinsation and this is an adaptive feature.

Question 26

Explain the migration of proteins into the cornified layer and why we need this

Answer 26

Granular layer has keratohyalin granules containing the precursor to a protein called filaggrin.
As the cell matures from the granular to the cornified layer, filaggrin forms a tight complex with other key proteins including loricrin and involucrin to merge with the cell membrane of the cells maturing at the cornified layer.
Thus complex merging with the cell membrane forms the cornified envelope which is key to providing the structural integrity of the cornified layer, giving it a waterproofing as well as withstanding abrasive forces.

The process of maturation from basal to cornified layer is tightly regulated. Some proteins are more expressed in the basal component such as the cyclo-keratin filaments type 5 and 14, other proteins are only expressed towards the surface including loricrin, profilaggrin and involucrin.

As the basal layer moves to cornified layer, it becomes terminally differentiated and loses a lot of organelles and metabolic function as well as the nucleus becoming less pronounced.

Question 27

What do thickened white layers in the gingiva usually mean?

Answer 27

Thickened layer of keratin

Question 28

What is the key difference between the lining and masticatory mucosa?

Answer 28

Lining mucosa does not keratinise under normal circumstances.

As no keratin, there is no granular cell layer. The layer is therefore celled the stratum intermedium. The most superficial zone is now called the superficial layer.

The lack of a cornfield envelope at the surface and lack of keratinisation means that lining mucosa tends to be more flexible and less waterproof than masticatory mucosa.

Question 29

What does specialised mucosa cover?

Answer 29

Covers the dorsal and dorsal-lateral aspects of the tongue.

Question 30

What separates the body and base of tongue?

Answer 30

The sulcus terminals.

anterior to this are the circumvallate papillae in an inverted V shape

Question 31

Where are the different papilla found on the tongue?

What is the order of frequency?

Answer 31

What covers most of the dorsal aspect of the tongue at the fulliform papillae and fungiform papillae are the end of the tongue.
Foliate papillae are towards the dorsal-lateral aspect of the tongue.

Order of frequency:

1. Filiform
2. Fungiform
3. Circumvillate
4. Foliate

Question 32

Give details on the filiform papillae

Answer 32

Filiform means thread like projections onto the surface.
These projections are covered by stratified squamous keratinised epithelium, usually para-keratinised.
A single filiform papillae is supported on fibrous tissue core from the lamina propria.
Filiform papillae are dispersed on the tongue between zones of non-keratinising squamous epithelium.
The papillae aid in mastication, helping food break up.

Covered by para-keratinised stratified squamous epithelium.
Sometimes more slender thread like projections branch off from the main papillae.

Question 33

Give some details on fungiform papillae

Answer 33

Clinically, these look red as the lamina propria supporting the fungiform papillae is highly vascularised. Also, the surface covering fungiform papillae has a thin epithelium compared to those covering the filiform papillae.
Fungiform papillae contain taste buds at the surface.

Question 34

Where are circumvallate papilla located?

Give details

Answer 34

Located at the junction between the anterior 2/3 of tongue and the base of the tongue in an inverted V shape.
Each circumvallate papillae is surrounded by a valley.
Usually covered by non-keratinised squamous epithelium.
Can see numerous taste buds seen on the outer surface of the papillae that a re located along the wall of the trench.
Within the submucosa are numerous serous minor salivary gland. These are glands of Von Ebner with a serous glands. Combinations of serous glands and taste buds indicates that one of the main functions of the circumvallate papillae are to function are solubilising food and for taste.

Question 35

What are the 3 non-keratinous sites within the oral epithelium?

Answer 35

Melanocytes
Langerhan cells
Merkel cells

Question 36

What are the nodules at the base of the tongue?

Answer 36

These nodules are due to lymphoid tissue.
The base of the tongue form a ring of lymphoid epithelial tissue.
Have openings extending down as invaginations into the surface of the mucosa called crypts.
All the cells here are lymphocytes organised as follicles and are important in the immune regulation of the upper digestive tract.
The invaginations are epithelial lined but this epithelium is much more loosely packed and the gaps are filled with lymphocytes.