Week 1: The oral cavity

Question 1

Epithelium of the GIT

Answer 1

Oral cavity and simple passages (i.e. oesophagus and anal canal) = stratified squamous non-keratinised epithelium

Digestive tract and everything else = simple columnar epithelium

Question 2

Describe the epithelium and general histological features of the lip

Answer 2

upper part = stratisfied squamous keratinised epithelium with hair

front ‘lip’ part = vermillion border = non-keratinised stratisfied squamous without glands (thus dry). Also very thin, which gives the lips their colour (underlying blood vessels).

Inside of lip = stratisfied squamous non-keratinised

Other features: skeletal muscle = orbicularis oris

minor salivary glands are also present

Question 3

Describe histological features of the tongue

Answer 3

Stratisfied squamous epithelium. Not normally keratinised, but may become parakeratinised with excessive wear and tear. Keratinisation may occur, but cells do not undergo cell death (remain nucleated)

Intrinsic skeletal muscle of tongue arranged in 3 directions: longitudinal, oblique and transverse fibers. *Only place where you see 3 different skeletal muscle directions

Lingual salivary glands: numerous seromucous glands often seen embedded between the muscle fibers

Question 4

Difference between histological structure of anterior 2/3 and posterior 1/3 of tongue?

Answer 4

Anteriorly = skeletal fibers more dense. Presence of seromucous glands - lingual salivary glands

Posteriorly = less dense skeletal muscle fibers. Presence of MALD (lymphoid tissue) of the lingual tonsils

Question 5

What are the different types of papillae on the surface of the human tongue, and their approximate location?

Answer 5

From posterior to anterior:

Circumvallate Papillae: largely around the lingular tonsils. Found where the tongue divides from anterior 2/3 to posterior 1/3 - the sulcus terminalis

Foliate Papillae: Little lateral slits on sides of tongue

Fungiform Papillae: Found throughout tongue. Look like little mushrooms.

Filiform Papillae: Found throughout tongue. Appear as little peaks.

Question 6

What is the Foramen Cecum, and where is it located?

Answer 6

Embryonic origin of the thyroid gland - in development, the thyroid began as a downgrowth from this point. The foramen cecum can be seen, but has no functional importance in the adult.

Located centrally, just posterior to the line of circumvallate papillae, in the posterior 1/3 of the tongue

Question 7

What are the features of Circumvallate Papillae?

Innervation?

Answer 7

The circumvallate papillae form a V-shaped line of ~9 (4-18) papillae just anterior to the sulcus terminalis and the foramen cecum.

They are gustatory papillae: Contain about half of all taste buds

von Ebner’s glands (serous only accessory salivary glands) are associated with both circumvallate papillae and foliate papillae

Supplied by Glossopharyngeal nerve (CNIX)

Question 8

What are the features of Foliate papillae?

Innervation?

Answer 8

Foliate papillae appear as small slits along the postero-lateral margin of the tongue.

The are gustatory papillae: Contain ~1/4 of all taste buds

Supplied by Glossopharyngeal (CNIX) and Facial (CNVII) nerves

Question 9

What are the features of Fungiform papillae?

Innervation?

Answer 9

Fungiform papillae are found over most of the surface of the tongue

Gustatory: Collectively, fungiform papillae contain 1/4 of all taste buds, but a large number of individual papillae may contain no taste buds.

Supplied by Glossopharyngeal (CNIX) and Facial (CNVII) nerves

Question 10

Which are the gustatory papillae?

Answer 10

Circumvallate
Fungiform
Foliate

(Filiform is non-gustatory)

Question 11

Describe the composition of a taste bud, and the innervation of the taste buds.

Features of taste buds

Lifespan of taste buds vs olfactory cells

Answer 11

Taste buds open onto the surface via the taste pore.

Taste buds are comprised of ‘taste cells’ (bipolar taste-detecting cells) and supporting cells, which both have microvilli which open into the taste pore.

Basally, there are basal cells

Afferent nerve fibres from bipolar cells of the anterior 2/3 of the tongue run with the Facial (CNVII) nerve

Fibres from posterior 1/3 of tongue run with glossopharyngeal (CNIX) nerve

Taste posterior to the pharynx is carried with the Vagus nerve (CNX)

Each individual taste bud detects its own taste: bitterness, sweetness, sourness, umami, and saltiness

Taste cell lifespan = ~10 days

Olfactory cells = ~30 days

Question 12

What are the 5 modalities of taste, and what are they triggered by?

Answer 12

Bitterness = alkalines

Sourness = acids

Saltiness = Na+

Sweetness = Fructose / glucose

Umami = Monosodium Glutamate taste

*Each modality has its own type of taste cell and receptor type

Question 13

Where might extralingual taste buds be found?

Answer 13

Palate, uvula, oesophagus, epiglottis

Question 14

von Ebners glands: function, structure, location

Answer 14

VE glands are found at the bases of the circumvallate and foliate papillary crypts

They are serous-only producing accessory salivary glands that produce lingual lipase, which is important in the initial digestion of fats

Their secretions also act as a liquid environment in which taste can be detected. The secretions also wash away taste molecules so new tastes can be detected

Question 15

Embryological sources of: Enamel, dentin, cementum, pulp and peridontal ligament

Answer 15

Enamel - ectoderm

Dentin, cementum, pulp, periodontal ligament - mesoderm

Question 16

When does tooth development begin?

Answer 16

The dental lamina (about 4 of them) appear at around 6 weeks - these begin to form deciduous teeth.
Permanent teeth develop from 20 weeks

Question 17

What does each dental lamina give rise to (specific teeth)?

Answer 17

Initially (at 6 weeks) the dental lamina gives rise to 4 enamel organs, each of which develops into the central and lateral incisors, the canines and the first molar teeth (all deciduous)

Later in development, the dental lamina develops posteriorly and gives rise to further enamel organs that will produce the rest of the molar teeth: one more deciduous and the 3 permanent molars

*Deciduous teeth are eventually lost and replaced by permanent teeth which develop adjacent to the deciduous ones

Question 18

What are the main two components of the embryological development of the tooth? And what are the sub-components of these two components?

Answer 18

Dental Papilla: Contains mesenchymal cells that will develop into odontoblast (dentin-secreting).
Mesenchymal cells within the dental papilla are also responsible for formation of tooth pulp.

Enamel organ: Consists of an outer enamel epithelium, which loops around to form the inner enamel epithelium. The sharp angles where the inner and outer enamel epithelium join is the cervical loop.
There is also the stellate reticulum, and the stratum Intermedium. These cells will form ameloblasts (enamel-producing).

Question 19

What are the main stages of embryological tooth development?

Answer 19

Bud stage: At around 6 weeks (embryological) = the development of a tooth bud without a clear arrangement of cells

Cap Stage: Enamel Organ is established, and the mesenchyme immediately adjacent to it (and within its curvature) condenses to form the dental papilla. ‘Cap’ stage because of the shape of the arranged cells.

During Cap Stage, the enamel organ develops a layer of ameloblasts - enamel producing - and the dental papilla develops a layer of odontoblasts - dentin producing.

Bell Stage: As enamel organ develops further is assumes a more ‘bell’-like shape. During this stage, the formation of a layer or both enamel and dentin has begun between the two epithelial layers (between the Ameloblasts and Odontoblasts). As more enamel and dentil is produced and laid down, the ameloblasts and odontoblast epithelial layers are pushed further apart.

Question 20

When does enamel stop being produced? What is the significance of this?

Answer 20

By the time the tooth erupts, there are no more ameloblasts, and no more enamel can be produced. Thus, the enamel you have on a permanent tooth is all you’ll ever get.

Question 21

What is dentin? Predentin?

Answer 21

Dentin: consists of 20% organic material - mainly type I collagen - and 80% inorganic material - mainly crystals of hydroxyapatite and fluoroapatite.

Predentin: The non-mineralised zone surrounding the apical processes of the odontoblasts. Contains type I collagen.

Question 22

What are junctional complexes on odontoblasts?

Answer 22

Joint adjacent odontoblasts.

Question 23

What are the parts of the Odontoblast cell?

Answer 23

Inferiorly, the body of the cell.
Just above the Junctional Complexes, the odontoblasts give rise to a long apical process and short lateral branches.
The dentinal tubule contains the odontoblast apical process. The bifurcated ends of the dentinal tubule extend into the adjacent enamel.

Question 24

What is the Dentinal tubule?

Answer 24

Columnar cell with apical process.
Walls of the dentinal tubule are formed by aligned collagen fibres. The tubule contains the apical process of the odontoblast. The bifurcated ends of the dentinal tubule extend into the adjacent enamel.

Question 25

What is Amelogenesis Imperfecta? Causes? Incidence?

Answer 25

No or impaired formation of enamel during tooth development. Teeth are typically smaller, discoloured, pitted or grooved and prone to rapid wear and breakage.

Causes: 3 main genes are identified. Depending on the gene, Amelogenesis Imperfecta may be autosomal dominant (AD), autosomal recessive (AR) or x-linked inheritance.

Incidence varies: 1 in 700 in Sweden, 1 in 14,000 in the US

Question 26

What are the main types of Salivary glands, and their main secretions?

Answer 26

Minor Salivary Glands (found in the oral mucosa)

Parotids: Serous

Submandibular: 80% serous, 20% Mucous

Sublingual: 80% mucous, 20% serous

Question 27

What are the 4 major components of saliva, and the main functions?

Answer 27

Mucins: Lubricate, and have immunological protective mechanisms against micro-organisms

Amylase: Initiates digestion of starch - mainly comes from parotids, with some contribution from submandibular

Lingual Lipase: Initiates digestion of fats

Slightly Alkaline ELectrolyte Solution: Moistens foods, and neutralises acids in oesophagus
Contains other components: lysozyme, lactoferrin, IgA, etc.

Question 28

What are the overall main functions of saliva?

Answer 28

Protection: coats tissues, lubricates, involved in humidification and taste

Host defence: Immunological, anti-bacterial, fungal and viral

Digestion: Contains some digestive enzymes, also contributes to taste, bolus formation (initial breaking down of food in mouth)

Question 29

What are the parts of an Ameloblast?

Answer 29

Long columnar cell. Basal non-secretory end and an apical secretory domain (Tome’s Process).

Basally, there are basal junctions, aggregations of mitochondria and a nucleus. Throughout the body there is much RER and Golgi.

Apical Junctional Complexes join adjacent Ameloblasts. Inferior to this point is the Tome’s Process. Secretory Granules in theis area contain Interrod Enamel which guides the assembly of the enamel rods as they are laid down.

Question 30

Describe the histological structure of the salivary glands

Answer 30

Compound tubular acinar glands drained by a duct system

Parotids = serous
Submandibular = 80% serous, 20% mucous
Sublingual = 20% mucous, 80% serous

In mixed seromucous glands, the serous component may exist as serous demilunes. Serous glands tend to be more basophillic. Mucous glands tend to have more flattened nuclei, and are paler staining.

As acinar glands, there is a spherical arrangement of secretory glands, which secrete their products into a central lumen which becomes an intercalated duct.

Myoepithelial cells are often associated with the secretory cells, within the basement membrane of the acinus. The contraction of the myoepithelial cells aids the expression of the secretory product.

Question 31

Features of Parotid Glands:

Answer 31

Salivary Glands: serous only. Striated Ducts

*Do not mistake adipose tissue which is often associated with the parotids for mucous acini.

Question 32

Features of Submandibular Glands:

Answer 32

Salivary Glands. Mostly serous acini (80%) with some mucous acini (20%) showing serous demilunes.

Question 33

Features of Sublingual Glands:

Answer 33

Salivary Glands: Mostly Mucous Acini (80%) with serous secreting cells (20%) only present as serous demilunes (part of mixed glands).

Question 34

Describe the duct system of salivary glands. How do the ducts differ between mucous and serous glands?

Answer 34

Ducts conduct and can even modify the secretory product.
All large glands have a number of lobes, thus there are intralobar ducts (within the lobe) and interlobar ducts (between lobes).

The lumen of the secretory acini become continuous with the intralobular duct. The intralobar ducts include intercalated ducts and striated ducts, both of which can modify the secretions.

Serous glands have well developed intercalated and striated ducts. Mucous glands do not.

Myoepithelial cells may be associated with striated ducts, as well as with acini.

Question 35

Features of Intercalated Ducts

Answer 35

Type of Intralobar duct

Lined by simple squamous - low columnar epithelium

Modify the secretions by:

Secreting bicarbonate (HCO3-) into the secretion which is an alkaline solution
Reabsorbing Cl- ions from the secretion.

Question 36

Features of Striated Ducts

Answer 36

As a type of Intralobular duct, Striated ducts connect Intercalated to Interlobar Ducts

Lined by simple tall cuboidal - low columnar epithelium

Striated appearance comes from basal and lateral cell membrane infoldings with elongated mitochondria between the folds.

Modify secretions by:
Secreting K+ and HCO3- (alkaline) into the secretion
*Normally produce a hypotonic alkaline secretion, but elevated secretion can cause hypertonic secretion

Question 37

Features of Interlobar Ducts

Answer 37

Interlobar ducts are between acini lobes
Lined by cuboidal and/or columnar epithelium that is initially simple but may become stratified
Do not modify the secretion*

Question 38

How to identify each of the tonsils of the oral cavity?

Answer 38

All will contain non-capsulated lymphatic tissues which may or may not have follicle aggregates of B cells.

Palatine Tonsils: Lined by stratisfied squamous epithelium. There will NOT be tongue tissue in the section.

Lingual Tonsils: Lined by stratisfied squamous epithelium. The 3-directional skeletal muscle fibres of the tongue will be present in the section.

Pharyngeal Tonsil: Differs in that it is lined by respiratory epithelium