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Growth and Development > Development of pharyngeal arches and face > Flashcards

Development of pharyngeal arches and face Flashcards

1
Q

The embryonic germ layers

A 
Ectoderm
Neural tube
Dorsal mesoderm
Ventral mesoderm
Endoderm
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2
Q

Ectoderm forms

A

Epidermis
Glands
Dental enamel

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3
Q

Neural tube forms

A

CNS and motor nerves

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4
Q

Dorsal mesoderm forms

A

Muscle and CT
Bone
Melanocytes
Sensory and autonomic nerves

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5
Q

Ventral mesoderm forms

A

BVs and cells

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6
Q

Endoderm forms

A

Gut lining and glands

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7
Q

At 3.5 weeks post-conception

A 
Tail
Hindlimb bud
Pericardial sac
Somites (mesodermal)
Forelimb bud
Occipital somite
3 pharyngeal / brachial arches
Mandibular arch
Head and buccopharyngeal membrane
SEE PICTURE
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8
Q

`Buccopharyngeal membrane function

A

Composed of ectoderm and endoderm

Separates foregut from stomodeum

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9
Q

Naming of parts (look at diagram)

A

Frontonasal process (developing forebrain)
Optic placode (thickening of specialised epithelium)
Stomodeum (primitive mouth)
Pharyngeal arches (gill slits)
Site of primitive hearts

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10
Q

The pharyngeal arches (parts)

A

6 arches but never see all
Pairs that fuse in the middle
Arches 4, 5 and 6 fuse to form single arch
Arches separated externally by clefts
Internally, arches separated by pouches that correspond with clefts

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11
Q

Structure of pharyngeal arches (look at diagram)

A

Outer surface covered by ectoderm
Inner surface lined with endoderm
Packed with ectomesenchyme

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12
Q

Each pharyngeal arch has

A

Artery, vein and cranial nerve
Skeletal element
Muscle block (probably from mesoderm and thus migrated into the arch)

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13
Q

Lamprey

A

Shows similar structure to developing pharyngeal arches

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14
Q

Pattern formation

A

Migration of nerve fibres from neural tube into arches is consistent and predictable
They will always innervate specific muscles and regions of skin and mucosa

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15
Q

Cranial nerves

A

1st arch: trigeminal
2nd arch: facial nerve
3rd arch: glossopharyngeal
4th arch: vagus nerve

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16
Q

Hox gene

A

Patterns of Hox gene expression within midbrain and hindbrain set up identity
As cells migrate from neural tube they keep this pattern
Regulates movement and differentiation of cells

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17
Q

Rhombomere

A

Transiently divided segment of developing neural tube

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18
Q

Growth of the arches

A

Things that were close in development e.g. 4th pharyngeal arch and heart become far away, explains why some nerves have strange courses

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19
Q

Pharyngeal arch muscles: arch 1

A

Muscles of mastication
Some suprahyoids
Tensor veli palatini
Supplied by third division of CN V

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20
Q

Pharyngeal arch muscles: arch 2

A

Muscles of facial expression
Some suprahyoids
Stapedius
All supplied by CN VII

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21
Q

Pharyngeal arch muscles: arch 3

A

One trivial muscle (stylopharyngeus)

Supplied by CN IX

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22
Q

Pharyngeal arch muscles: arch 4

A

Pharyngeal constrictors
Muscles of soft palate and larynx
All supplied by CN X

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23
Q

What does Meckel’s cartilage form (1st arch)

A

Two of th ear ossicles: incus and malleus

24
Q

2nd arch cartilage

A

Styloid process, stylohyoid ligament, upper part of hyoid bone (greater cornu)

25
Q

3rd arch cartilage

A

Hyoid bone

26
Q

4th arch cartilage

A

Upper part of thyroid cartilage

27
Q

5th arch cartilage

A

Lower thyroid cartilage

Cricoid cartilage

28
Q

Pharyngeal clefts

A

Between arch 1 and 2: auditory tube and middle ear, external auditory meatus, tympanic membrane
Middle ear cavity contains malleus, incus, stapes
All other clefts grow over

29
Q

Pharyngeal pouches

A

2: palatine tonsil
3: inferior parathyroids
4: superior parathyroids, thyroid cells secreting calcitonin and thymus

30
Q

Development of tongue

A

Motor: hypoglossal (CN XII)
Taste: chorda tympani (CN V) in first 2/3, glossopharyngeal in posterior 1/3
Sensation: Lingual and glossopharyngeal

31
Q

Which part of tongue derived from which arch

A 
Lingual: 1st
Chorda tympani: 2nd
Glossopharyngeal: 3rd
Hypoglossal: occipital somites
2nd arch forms tastebuds
32
Q

Arch malformations

A 
Majority affect 1st arch 
Clearest impact on skeletal structures
-hypotrophic mandible
-conductive hearing loss (incus and malleus)
-malformed external ear
Can be part of a syndrome
33
Q

Incidence of cleft lip and palate

A

c. 800-1000 live births per year in UK
Males>females
Very rare familial cleft carried through X chromosome

34
Q

Window for palate to fuse

A

Several hours as embryo

35
Q

Parts of embryo at 4 weeks

A 
Frontonasal process
Mandibular arch
Somites
Primitive tail
Heart tube (atrium/ ventricle)
Mouth is simple slit (stomideum), no nasal cavity
36
Q

Formation of nasal cavity and primary palate

A

(look at images on lecture)
Nasal placode invaginates (pushes into) into embryo, gradually growing backwards
Cave develops into nasal pit
Frontonasal process becomes more ridged
Medial nasal processes develops in middle
Lateral nasal process develop on outside
Tissue in middle forms primary nasal septum which gradually grows forward
Nasal cavity becomes deeper and deeper
Nasal placode becomes olfactory epithelium later

37
Q

What/ where is primary palate

A

Just behind central incisors in mature anatomy

Just behind filtrum

38
Q

What/ where is primary palate

A

The primary palate begins the separation of the nasal and oral cavities anteriorly
Just behind central incisors in mature anatomy
Just behind filtrum

39
Q

Nasal placode

A 
Future of developing nose
Specialised epithelium
Where nasal cavities grow from
Front of frontonasal process
Thickened epithelium above
40
Q

Difference in location of primary and secondary nasal septum

A

Secondary is further back

41
Q

Primitive nasal cavity

A

The invagination of the nasal placodes forms nasal pits

42
Q

Maxillary processes

A

Extend from 6 weeks from posterior aspect of mandibular arch and form lateral borders of mouth

43
Q

Maxillary processes

A

Extend from 6 weeks from posterior aspect of mandibular arch and form lateral borders of mouth

44
Q

Processes of the maxillary arches

A

Two pairs of processes grow mesially from the maxillary arches
Superior is tectospetal process, grows across and then downwards (becomes secondary nasal septum eventually)
Inferior is the palatine process, grows downwards towards developing tongue which fills oronasal space at this point
Up to about 8 weeks
Look at animation on slides

45
Q

Growth of palatine processes

A

Dependent on several factors, e.g.
-FGF10 expressed in ectomesenchyme and acts on FGF2R in ectodermal covering
FGF10 -/- mutation leads to no or reduced growth of palatine processes

46
Q

Palatal elevation

A

At 8 weeks
Embryo develops a cervical flexure, lifting head away from cardiac bulge
Mandible widens allowing tongue to drop into floor of mouth (no longer in oronasal process)
Palatal processes now have no restraint and elevate into horizontal position

47
Q

Palatal elevation - intrinsic factors

A

In tongue experimentally depressed prematurely, palatine processes do not elevate until close to correct time
Hyaluronan accumulates around ectomesenchyme within processes
Bonds large amounts of water
> turgor
Agents that disrupt GAG synthesis tend to inhibit palate elevation

48
Q

Fusion of palatine processes

A

At 10 weeks ALL processes have grown to point where they make contact and fuse
Fusion of palatine processes with
-each other (forming hard palate)
-primary palate (soft?)
-nasal septum
Takes 2 weeks
Fusion requires breakdown of ectodermal covering of processes to allow underlying ectomesenchyme to merge (like fingers)
Ectomesenchyme releases signals that institute programmed cell death (apoptosis) in ectodermal cells
Mammal/ bird/ reptilian recombinations show that ectomesenchyme determines fate of ectoderm

49
Q

Ectoderm on palatine processes expresses gene (fusion of palatine processes)

A

Msxl –> genetic cascade releases BMP4 into ectomesenchyme –> ectomesenchyme releases BMP2 –> ectodermal apoptosis

50
Q

Palatine processes fusion complete at

A

12 weeks

51
Q

Palate 12 weeks -16 weeks

A

Anterior 2/3 palate invaded by bone (hard palate

Posterior 1/3 invaded by muscle from 4th pharyngeal arch to form muscles of soft palate

52
Q

Differentiation of bone

A

Can leave epithelial cell rests

53
Q

Frontonasal process compressed between maxillary processes to form

A

Protruding nose

54
Q

Fusion of maxillary and mandibular processes to form

A

Mouth

55
Q

Macrostomia

A

Maxillary and mandibular processes fail to fuse

56
Q

Clefts

A

May occur between any internal or external processes

  • normal with fusion lines
  • unilateral cleft lip
  • unilateral cleft lip and palate
  • bilateral cleft of primary palate
  • midline cleft of secondary palate
  • unilateral cleft of primary palate with extension
57
Q

Contributory factors of clefts

A

Heavy smoking
Heavy alcohol consumption
Folic acid deficiency
(in early stages of pregnancy)

Growth and Development (23 decks)

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