Week 1: The oral cavity Flashcards
Epithelium of the GIT
Oral cavity and simple passages (i.e. oesophagus and anal canal) = stratified squamous non-keratinised epithelium
Digestive tract and everything else = simple columnar epithelium
Describe the epithelium and general histological features of the lip
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
Describe histological features of the tongue
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
Difference between histological structure of anterior 2/3 and posterior 1/3 of tongue?
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
What are the different types of papillae on the surface of the human tongue, and their approximate location?
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.
What is the Foramen Cecum, and where is it located?
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
What are the features of Circumvallate Papillae?
Innervation?
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)
What are the features of Foliate papillae?
Innervation?
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
What are the features of Fungiform papillae?
Innervation?
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
Which are the gustatory papillae?
Circumvallate
Fungiform
Foliate
(Filiform is non-gustatory)
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
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
What are the 5 modalities of taste, and what are they triggered by?
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
Where might extralingual taste buds be found?
Palate, uvula, oesophagus, epiglottis
von Ebners glands: function, structure, location
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
Embryological sources of: Enamel, dentin, cementum, pulp and peridontal ligament
Enamel - ectoderm
Dentin, cementum, pulp, periodontal ligament - mesoderm
When does tooth development begin?
The dental lamina (about 4 of them) appear at around 6 weeks - these begin to form deciduous teeth.
Permanent teeth develop from 20 weeks
What does each dental lamina give rise to (specific teeth)?
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
What are the main two components of the embryological development of the tooth? And what are the sub-components of these two components?
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).
What are the main stages of embryological tooth development?
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.
When does enamel stop being produced? What is the significance of this?
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.
What is dentin? Predentin?
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.
What are junctional complexes on odontoblasts?
Joint adjacent odontoblasts.
What are the parts of the Odontoblast cell?
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.
What is the Dentinal tubule?
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.
