embryology of palate and related craniofacial/ oral structures

early embryonic development: bastulaiton

2 cells → 4 → 8 → morula (mass of cells) → early blastula → late blastula

refer to image

implantation

early embryonic development: gastrulation (D 14-17)

key things

• epi+hypoblast

• invaginating mesoderm cells

• ecto/meso/endoderm

human gastrula

b = above

c = below

embryonic folding - disk to tube

• ectoderm = outside

• mesoderm = middle

• endoderm = inside

embryonic disk folds → human tube

3 germ layers give rise to diff tissues

neurulation (W 3-4)

*formation of neural tube

neural crest

• leaves to from most of major structures of face (come from back)

• form peripheral nerves

(R = just ectoderm)

neural tube closure

neural tube defects

• often due to folic acid deficiencies

• pregnant women advised to take folic acid supplements

neural crest formation and migration

cranial neural crest cells

• form dentin and most of craniofacial skeletal tissues

• skeletal tissue of craniofacial region: from neural crest (comes from ectoderm)

  • anywhere else = from mesoderm

• migrate to head and face

neurocristopathy

abnormal development of neural crest cells

contributions of neural crest cells in head

• nearly ½ of head and face skeleton comes from migration of cells from back to front of embryo

• significant contribution to cranial ganglia

pharyngeal arches

(skeletal derivatives?)

• post-migratory neural crest cells populate future face

development of face

maxillary process

mandibular arch → mandible

MNP and inter maxillary segment (primary palate)

yellow = MNP (medial nasal prominences)

• 2 MNPs merge at midline to form intermaxillary segment

orange = maxillary prominence/ process

development of palate

• primary palate develops at end of W5 from intermaxillary segment

• secondary includes hard and soft palate

hard palate

• comes from fusion between inter maxillary and a pair of maxillary processes

elevation and fusion of palatal shelves

• 2 lateral palatine processes project from internal of maxillary prominences and grow downward on either side of tongue

• lateral palatal shelves grow and move to horizontal position (to tongue)

• (fusion of primary palate with lateral palatine processes and nasal septum)

fusion of palatal shells and naval septum

naval septum divide nasal cavity into 2 separate cavities

when fusion goes wrong

cleft lip and cleft palate

• CP freq associated with uni/bilateral CL

high-arched palate

• tall and narrow U-shaped palate (arc instead of flat)

• similar pathogenic mechanism of CP

• feeding difficulties

• can cause tooth crowding

cleft malformation

anterior

• incl CL with/without cleft of alveolar part of maxilla

• BCD

posterior

• incl. clefts of posterior palate

• EF

developmental mechanisms of CL &/ P

• improper growth of primordia involved in palate development

• small jaw → tongue fall backwards and block secondary palate closure

  • e.g. Pierre-Robin Seq

• failure of fusion between spatial shelves/ inter maxillary segment and palatal shelves

(palate fusions)

1. shelf to shelf (the midline): forms the secondary palate;

2. shelves to the intermaxillary segment (at the incisive foramen): joins the front and back of the palate;

3. shelves to the nasal septum (from above): separates the nose from the mouth.

etiology - causes of CL/P

genetic

• syndromic (part of wider spectrum of disease), non-syndromic (>common) (otherwise healthy), many genes associated

gene and environmental interaction

• gene → > susceptible

• eg. smoking (GSTT1 and NOS3), alcohol consumption (ADH1C)

drug

• excessive retinoid acid (vit A)

craniofacial microsomia (CFM)

Treacher Collins Syndrome

DiGeorge Syndrome

Pierre-Robin sequence

small jaw → tongue fall back → high-arched palate etc.