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Growth and Development > Prenatal Craniofacial Development > Flashcards

Prenatal Craniofacial Development Flashcards

1
Q

Morphogenesis of the face is a complex

3D process involving (4)

A

patterning,

outgrowth, fusion and moulding of tissues

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2
Q

~— days, head & neck region comprises ~ half of embryo.

A

22days

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3
Q

During 4th week, ventral mesoderm condenses into a series

of

A

segmented bilaterally paired, mesenchymal swellings

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4
Q

pharyngeal (branchial) arches

> ultimately — pairs, arising in — order

A

5

cranial-caudal

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5
Q

Initially, five prominences (tissue masses) surround the

stomodeum:

A

Øfrontonasal prominence
Øfirst arch (> mandibular process)
Ømaxillary process (delayed appearance)

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6
Q

First (mandibular) arch
and maxillary processes
are both — structures

A

paired
> grow ventro-laterally
around the OM

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7
Q

The majority of the growth and morphological change

in facial tissue masses is driven by the

A

invading cranial

neural crest-derived mesenchyme.

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8
Q

Contrary to textbook literature, the paired first pharyngeal
arches only give rise to the

A

mandibular processes.

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9
Q

Maxillary processes originate as

A

separate (delayed)

swellings rostral to the mandibular processes.

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10
Q

Maxillary processes originate as separate (delayed)
swellings rostral to the mandibular processes.
> Invaded by distinct population of

A

late migrating CNCC

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11
Q

Formation and invagination of nasal placodes (thickening

of ectoderm) in

A

Frontonasal Prominence (FNP)
•Induction and invagination of nasal placodes similar to
neural plate induction and invagination

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12
Q

Two types of morphological processes for ‘joining’ tissues

A

merging

fusion

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13
Q

1st: Merging

A

joining of two masses already partly in contact

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14
Q

merging examples (2)

A
  • Merging of Maxillary (MXP) & Lateral Nasal Processes (LNP)

* Medial merging of Mandibular Processes (MNP)

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15
Q

2nd: Fusion

A

joining of two separate tissue masses

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16
Q

fusion example

A

•Contact-dependent fusion between MNP and MXP/LNP

ØForms the primary palate and nares (nostrils)

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17
Q

Secondary palate (future roof of mouth)
arises later from the medial aspects of the
MXPs >

A

palatal shelves

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18
Q 
After immigration of 
cranial neural crest cells, 
growth & morphogenesis 
of the face is controlled 
by
A

ongoing epithelial-

mesenchymal interactions

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19
Q

Cranial neural crest cells (CNCC) primarily determine

A

facial form/shape

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20
Q

The Ectoderm in Growth & Patterning

•defined boundaries of

A

expression in facial ectoderm

21
Q

skipped
Neural expression of Shh/Fgf8 precedes (and is
required for) the ectodermal expression: (3)

A

•juxta-positioned FGF8/SHH
» frontonasal ectoderm zone (FEZ)
•transplanted ectoderm retains FGF8/SHH pattern of
expression from originating tissue.
•Secreted factors from the FEZ can direct outgrowth of
the underlying CNCC and determines D-V pattern of the FNP
Øbut precise shape depends upon pattern
information inherent in the neural crest.

22
Q

A Dynamic Ectoderm (3)

A

support and direct outgrowth of the facial processes
guides differentiation of CNC
facilitating timely fusion of the facial processes

23
Q

interrelationship between the

A

CNC and ectoderm

24
Q

facilitating timely fusion of the facial processes

fusion establishes the

A

primary palate

goes on to form the alveolus and lip proper

25
Q

Third most common birth defect (~1 in 700 births worldwide)

A

Cleft lip +/- cleft primary palate

26
Q

Cleft lip +/- cleft primary palate

Embryological origin? (2)

A

ectodermal or CNCC

27
Q

Cleft lip +/- cleft primary palate

What else may be affected?

A
28
Q

Cleft lip +/- cleft primary palate
What is impact on ongoing development of the face
(2) and ultimately function (3)

A

growth, ossification

feeding,
breathing, oral hygiene

29
Q

The Secondary Palate (2)

A

•Palatal shelves (condensations of CNCC mesenchyme)
•Secondary palate forms well after the primary palate/lip
(10th week vs 7th week)

30
Q

Ossification of the secondary palate
(osteoblasts derived from CNCC) begins
just before

A

palatal development complete

31
Q

formation of the secondary palate (3)

A
  1. Growth (either side of tongue)
  2. Elevation & rotation
  3. Medial growth & fusion at midline and with nasal septum
32
Q

cleft secondary palate prevalence

A

~1 in 1000 births world-wide

33
Q

cleft secondary palate can result from (3)

A

1) poor growth of shelves,
2) failed elevation, or
3) failed fusion

34
Q

Critical that tongue lowers to allow the shelves to rotate to
a position

A

above the tongue

35
Q

— (enlarged tongue) can
provide a physical barrier to
secondary palate closure

A

Macroglossia

36
Q

Small or retrognathic mandible also associated with

A

failed palatal fusion (Pierre-Robin sequence)

> Tongue forced backward and elevated

37
Q

Craniofacial cartilage first appears in the — and

shortly thereafter in the (2)

A

mandible

midface and cranial base

38
Q

Craniofacial cartilage first appears in the mandible and

shortly thereafter in the midface and cranial base (2)

A

> Provides structural support for shaping the growing head
Precedes ossification [NB: in the face, few cartilages are replaced
by bone unlike the axial skeleton (ie. long bones)]

39
Q

•Cartilage of PA1 (Meckel’s cartilage) arises during

A

7th week (human) > forms template for the mandible. (E11.5 in mice)

40
Q

•PA1 also contributes to

A

two ear ossicles

> parts of malleus and incus (and ligaments)

41
Q

BUT, like most facial
cartilages, most is not
converted to —.

A

bone

42
Q

Rather… parts —, with caudal

aspects forming part of middle ear bones.

A

degenerate

43
Q

Development of the Ear is formed independent from

A

embryonic structures

44
Q

External and middle ear: (2)

A
  • Derivatives of PA1 and PA2
  • Intervening pharyngeal cleft
  • Pharyngeal pouch
45
Q

nner ear:

•Arises from

A

thickening of ectoderm
(otic placode) dorsal to PA3 at level of
hindbrain and subsequent
invagination (otic pit)

46
Q 
**Inner and outer 
ear malformations 
often associated 
with --- 
defects
A

mandibular

47
Q

Knowledge of the embryological origins of
clinical presentations is important to appreciate
the totality of the patient’s problem as it may: (3)

A
  • merit additional clinical considerations
  • prompt more detailed assessment
  • impact treatment plans
48
Q

What might seem causally unrelated may in fact

be of clinical significance

A

> diagnosis

Growth and Development (15 decks)

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