PALM 309: Quiz 7

Differential growth

different parts of the embryo grow at different rates and extents

Merging

filling in of tissues

Fusing

process involving tissue growth, fusion, breakdown and filling in.

Ectoderm

covers the surface of the embryo - gives rise to epidermis and epithelial lining of oral cavity

Stomadeum

develops as a depression in the ectoderm to form future oral cavity

Pharynx

most superior part of the endoderm

Buccopharyngeal membrane

Separates the stomadeum from developing pharynx, later degenerates, oral cavity and pharynx communicate

Facial primordia

develop as elevations of tissue surrounding stomadeum

Primordia

covered in ectoderm and filled with mesenchyme

Frontonasal prominence

develops above the stomadeum

Pharyngeal arches

multiple elevations below stomadeum

Nasal placodes

bilateral thickenings of ectoderm, on either side of frontonasal promincence

Differential growth

Parts of the embryo grow at different rates and extents

Fusion vs merging

Merging = filling in; Fusion = growth + breakdown + joining of tissues

Stomadeum

Ectodermal depression that becomes the future oral cavity

Buccopharyngeal membrane

Separates stomadeum from pharynx; later degenerates

Frontonasal prominence

Forms the forehead and contributes to nose structures

Pharyngeal arches

6 arches form; 5th regresses; give rise to head/neck structures

Mandibular arch

First arch; gives rise to maxillary processes

Maxillary processes

Form lateral upper lip, cheek, and secondary palate

Nasal placodes

Ectodermal thickenings that form nasal pits

Nasal pits

Invaginate to form nasal cavities

Nasomedial processes

Form intermaxillary segment (philtrum, incisors, primary palate)

Nasolateral processes

Form alae (sides) of the nose

Intermaxillary segment

Forms philtrum, primary palate, incisors, nasal septum

Philtrum

Midline of upper lip formed by fused nasomedial processes

Upper lip formation

Fusion of nasomedial + maxillary processes

Lower lip formation

Derived from mandibular arch

Nasolacrimal duct

Forms from ectoderm in nasolacrimal groove

Oblique facial cleft

Failure of maxillary + nasolateral process fusion

Primary palate

Formed by nasomedial processes

Secondary palate

Formed by lateral palatal shelves (maxillary processes)

Cleft palate cause

Failure of palatal shelves to fuse

Cleft lip cause

Failure of nasomedial + maxillary processes to fuse

Macrostomia

Large mouth due to failed fusion of maxillary + mandibular arch

Microstomia

Small mouth due to excessive fusion

Pharyngeal arch components

Mesenchyme, cartilage, artery, cranial nerve

First pharyngeal cleft

Forms external auditory canal

First pharyngeal pouch

Forms tympanic cavity + eustachian tube

Second pouch

Forms palatine tonsils

Third pouch

Forms thymus + 2 parathyroid glands

Fourth pouch

Forms parafollicular thyroid cells + 2 parathyroid glands

Thyroglossal duct

Forms as thyroid descends; degenerates

Foramen cecum

Remnant of thyroglossal duct on tongue

Anterior 2/3 of tongue

Formed by lateral lingual swellings (1st arch)

Posterior 1/3 of tongue

Formed by hypopharyngeal eminence (3rd + 4th arches)

Sulcus terminalis

Marks fusion of anterior and posterior tongue

Midline groove of tongue

Marks fusion of lateral lingual swellings

Ankyloglossia

Short lingual frenulum ("tongue-tied")

Cleft tongue

Failure of lateral lingual swellings to fuse

Neural crest cells

Contribute to head mesenchyme

First arch syndromes

Failure of neural crest cell migration

Pre-eruptive phase

Tooth movement before root formation (bud, cap, bell)

Pre-functional eruptive phase

From root formation to occlusion

Eruption pathway

Must be cleared via bone resorption

Dental follicle

Regulates eruption via osteoclast activation

Osteoclasts

Resorb bone to allow eruption

PDL fibroblasts

Remodel collagen and help move tooth

Fundic bony ladder

Temporary bone support during eruption

Clinical eruption

Tooth breaks through oral mucosa

Junctional epithelium

Formed from REE around tooth

Functional eruptive phase

After occlusion until tooth death

Hyper-eruption

Excess eruption when no opposing tooth

Gubernacular canal

Pathway around dental lamina of permanent teeth

Gubernacular cord

Remnant guiding permanent tooth eruption

Odontoclasts

Resorb primary tooth roots

Exfoliation

Shedding of primary teeth after root resorption

Ectopic eruption

Tooth erupts in abnormal position

Impaction

Tooth fails to erupt due to lack of space

Natal teeth

Teeth present at birth

Attrition

Loss of enamel from occlusal wear

Abrasion

Loss of enamel from brushing

Erosion

Demineralization from acids

Sclerotic dentin

Blocked dentin tubules from peritubular dentin

Hypercementosis

Excess cementum deposition

Pulp fibrosis

Increased collagen, decreased cells in pulp

Gingival recession

Gingiva moves apically exposing root

Dry mouth (aging)

Reduced saliva due to gland changes and meds

The lining of the oral cavity is derived from which embryonic germ layer?

Ectoderm

Fusion of the 2 nasomedial proccess froms what 2 embryonic premordia?

Philtrum of the upper lip and primary palate

failure of fusion of the nasomedial process with the maxillary process results in what 2 developmental defects?

cleft lip and cleft palate

A bilateral cleft lip results from failure of fusion of what embryonic primordia?

Failure of the right and left maxillary process to fuse with the nasomedial process

What facial primordia gives rise to the forehead?

Frontonasal prominence

What facial primordia fuse to form the nasolacrimal duct?

Maxillary process and nasolateral process

What does the mandibular arch give rise to?

Mandible, part of the outer ear and some ear ossicles, muscles of mastication

What embryonic structure is the inner ear canal derived from?

First pharyngeal pouch