Development of the face and oral cavity

Question 1

Palate development/cell sources/stages

Answer 1

• Starts at approximately 28 days.
• Secondary palate starts at 7-8th week and is completed by the end of 3rd month.
• Critical period of development is from the end of 6th week to beginning of 9th week.
• Formed by fusion of the primary and secondary palate.
• A globular process forms by fusion of the medial nasal processes.
o Gives rise to the intermaxillary segment.
o This then gives rise to the primary palate (plus the anterior teeth and the supporting structures).
• The secondary palate develops from lateral palatine shelves that originate from the medial growth of the maxillary processes into the oral cavity.

Question 2

Tongue development/cell sources

Answer 2

• The tongue develops from two sources:
o The body of the tongue from 1st arch in the floor of the mouth and is covered by ectoderm.
o The root of the tongue from arches 2, 3 and 4– in the floor of pharynx and is covered by endoderm.
o The sulcus terminalis and foramen cecum mark the division between these two portions.
Foramen cecum is the beginning of the thyroid gland

Question 3

Notochord

Answer 3

o Mesodermal derived cells at the anterior region form the notochord and migrate forward to the prochordal plate. The notochord will provide structural support “backbone” to the developing embryo

Question 4

Development of thyroid gland

Answer 4

• First appearance of this gland is during the third week of development as an invagination in the floor of the pharynx at the foramen caecum.
• Communication with the pharynx is developed by a duct that develops- the thyroglossal duct that allows the thyroid gland to migrate to the neck.
• This duct is generally obliterated at 6 weeks but remnants may persist and can develop into cysts.
o Sometimes it does not get obliterated. Creates clusters of epithelium and secretes and becomes a cyst.
Depression in the floor of the pharynx. Migrates down a channel of epithelium in the neck (thyroglossal duct).
• The gland becomes bilobed and the endoderm breaks down into cell clusters that will become follicles.
• Parafollicular cells join the gland from the 5th pouch.

Question 5

• Five Facial Primordia

Answer 5

o Frontonasal process
o 2 Maxillary process
o 2 Mandibular process

Question 6

o Frontonasal process

Answer 6

 Will form the forehead and bridge and apex of nose
 Further differentiation into
• Nasal placodes (ectodermal thickening)

Question 7

o 2 Maxillary process

Answer 7

	Will form
•	Upper cheeks
•	Most of upper lip
•	Lateral palatine processes
	Will enlarge and grow medially
	Will merge with median nasal prominence

Question 8

o 2 Mandibular process

Answer 8

	First to fuse
	Median ends of each process merge together
	Are on caudal boundary of stomodeum
	Merge with maxillary process
	Give rise to
•	Chin
•	Lower lip
•	Lower cheek

Question 9

• Nasal placodes (ectodermal thickening)

Answer 9

-from frontonasal process
o	Deepen into pits (convexconcave)
	Are primordial of anterior nares and nasal cavities form original ectodermal thickening
	Pits deepennasal sacnasal cavity
	Separated from stomodeum
o	Mesenchyme proliferates to form
	Median nasal process
	Lateral nasal process
•	Form alae of nose
o	Union of medial nasal prominence with the lateral nasal prominence and maxillary prominence is required for normal development of upper lip

Question 10

 Median nasal process

Answer 10

from nasal placodes from frontonasal process
• Merge with each other and the maxillary process
• Intermaxillary process (segment)
o Forms philtrum
o Premaxilla with 4 anterior teeth
o And anterior palate (median palatine process)
• Nasolacrimal groove forms at jct. of LNP and max. process
o Ectoderm thickens and forms epithelial cord on the floor of NLG
o Epithelial cord canalizedduct
o Cranial end expands into lacrimal sac
• Septum ethmoid and cribiform plate grows from these

Question 11

• Palatogenesis

Answer 11

o Begins at end of 5th week
o Completed at 12th week
 Critical period is week 6-9
o 2 parts: anterior and posterior
o Median palatal process and lateral palatine processes meet at incisive foramen
o Palate fuses with nasal septum
o Median palatine raphe indicates line of fusion of posterior shelves
o Bone develops except in posterior region

Question 12

• Median palatal process

Answer 12

o Forms from intermaxillary segment
o Forms the anterior palate
o Fuses with LPP

Question 13

• Lateral palatine processes

Answer 13

o Formed as projections from maxillary prominences
o Form posterior palate
o Hang down (vertical) and must swing up and join septum and anterior palate
 Elongate and ascend to horizontal position
 Tongue moves inferiorly and decreases in size
 2 shelves approach and fuse in median plane

Question 14

• Nose

Answer 14

o	Nasal septum
	Grows from median nasal process
o	Bridge of nose
	Forms from frontonasal process
o	Ala of nose
	Forms from lateral nasal process

Question 15

• Nasal choanae

Answer 15

o Oronasal membrane ruptures by end of 6th week forming communication between oral and nasal cavities primitive choanae
 If membrane doesn’t rupture, end up with bony obstructionchoanal atresia
 Most common nasal abnormality in newborns (1/7000)
 Females twice as likely
 More than half affected infants have other congenital problems
o Develop as elevation on lateral wall
o Specialized ectodermal epithelium (olfactory)
o Diverticula will develop sinuses
 Form wall of nasal cavityextend into bones
 Alters size and shape of face and lightens the bones
 Maxillary, ethmoid, sphenoid, frontal
 Drain into nasal cavity

Question 16

• Hypertelorism

Answer 16

• wide spaced eyes

Question 17

• Anterior palate (primary palate)

Answer 17

o Forms from median palatine process of intermaxillary segment

Question 18

• Posterior palate (secondary palate)

Answer 18

o Forms from lateral palatine processes of maxillary processes

Question 19

• Cleft lip /Cleft palate

Answer 19

o	Incidence
	Boys are more affected by cleft lip and palate, 3:2
	Isolated clefts of palate more common in girls
	75% are unilateral, rest are bilateral
	Left side more involved than the right
o	Teratological factors
	Heredity
	Chemicals and drugs
•	Smoking doubles incidence
•	Retinoic acid, phenytoin, corticosteroids, alcohol
	Vitamins (A)
	Irradiation
	Rubella
	Week 5-12 is sensitive time

Question 20

• Median palatal raphe

Answer 20

o Where palatal shelves meet and fuse

Question 21

• Incisive foramen

Answer 21

o Where median palatine process and lateral palatine processes fuse

Question 22

• Tuberculum impar

Answer 22

o From first arch (oral part of tongue)
o Forms median tongue bud  anterior 2/3
o 2 oval swelling appear on each side of this
 Lateral lingual swellings

Question 23

 Lateral lingual swellings

Answer 23

• These overgrow the median tuberculum impar

* They then fuse forming median sulcus and lingual septum internally

Question 24

• Anterior tongue (body)

Answer 24

o From 1st arch- lateral lingual swellings and median tongue bud (tuberculum impar)

Question 25

• Posterior tongue (root)

Answer 25

o From arch 3

o Hypopharyngeal eminence component

Question 26

• Copula

Answer 26

o From arch 2- from ventromedian portion

o Initial contribution to surface is lost

Question 27

• Median sulcus

Answer 27

o Formed by fusion of lateral lingual swellings

Question 28

• Sulcus terminalis

Answer 28

o Line of fusion of lateral lingual swelling and hypobranchial eminence

Question 29

• Hypobranchial eminence

Answer 29

o Forms posterior 1/3 of tongue from arch 3 and 4
o Caudal to the copula and overgrows copula
o Epiglottis develops from caudal portion

Question 30

• Macroglossia

Answer 30

o Tongue prone to trauma and drying
o Upper respiratory tract infections common
o Difficulty swallowing and airway obstruction
o Speech impairment and drooling
o TX: glossectomy with anterior wedge technique
o Can accompany downs, congenital hypothyroidism and Pierre Robin

Question 31

• Thyroid gland

Answer 31

o First endocrine gland to develop
o Median endodermal thickening from floor of primordial pharynx
o Begins at foramen cecum of tongue
o Descends in neck-pathway forms temporary duct
 Thyroglossal duct
• Connects gland to tongue
• By 7 weeks gland becomes solid and bilobed and duct degenerates
o 11 weeks- colloid formed
o Parafollicular cells come from 4th arch
o Can have abnormal positioning
 Cervical thyroid
 Pyramidal lobe-remnant of distal end of duct
 Or on tongue at foramen cecum

Question 32

• Thyroglossal duct cyst

Answer 32

o Generally in midline of neck
o URI can trigger growth
o Will move up and down when swallowing

Question 33

• Rathke’s pouch

Answer 33

o Forms anterior portion of pituitary gland from oral ectoderm

Question 34

• Diencephalon

Answer 34

o 3rd ventricle near optic chiasm dips and forms posterior pituitary out of neuroectoderm