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

Development of pharyngeal arches and face Flashcards

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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)

Study These Flashcards
A

Two of th ear ossicles: incus and malleus

24
Q

2nd arch cartilage

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A

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

25
3rd arch cartilage
Hyoid bone
26
4th arch cartilage
Upper part of thyroid cartilage
27
5th arch cartilage
Lower thyroid cartilage | Cricoid cartilage
28
Pharyngeal clefts
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
Pharyngeal pouches
2: palatine tonsil 3: inferior parathyroids 4: superior parathyroids, thyroid cells secreting calcitonin and thymus
30
Development of tongue
Motor: hypoglossal (CN XII) Taste: chorda tympani (CN V) in first 2/3, glossopharyngeal in posterior 1/3 Sensation: Lingual and glossopharyngeal
31
Which part of tongue derived from which arch
``` Lingual: 1st Chorda tympani: 2nd Glossopharyngeal: 3rd Hypoglossal: occipital somites 2nd arch forms tastebuds ```
32
Arch malformations
``` 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
Incidence of cleft lip and palate
c. 800-1000 live births per year in UK Males>females Very rare familial cleft carried through X chromosome
34
Window for palate to fuse
Several hours as embryo
35
Parts of embryo at 4 weeks
``` Frontonasal process Mandibular arch Somites Primitive tail Heart tube (atrium/ ventricle) Mouth is simple slit (stomideum), no nasal cavity ```
36
Formation of nasal cavity and primary palate
(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
What/ where is primary palate
Just behind central incisors in mature anatomy | Just behind filtrum
38
What/ where is primary palate
The primary palate begins the separation of the nasal and oral cavities anteriorly Just behind central incisors in mature anatomy Just behind filtrum
39
Nasal placode
``` Future of developing nose Specialised epithelium Where nasal cavities grow from Front of frontonasal process Thickened epithelium above ```
40
Difference in location of primary and secondary nasal septum
Secondary is further back
41
Primitive nasal cavity
The invagination of the nasal placodes forms nasal pits
42
Maxillary processes
Extend from 6 weeks from posterior aspect of mandibular arch and form lateral borders of mouth
43
Maxillary processes
Extend from 6 weeks from posterior aspect of mandibular arch and form lateral borders of mouth
44
Processes of the maxillary arches
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
Growth of palatine processes
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
Palatal elevation
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
Palatal elevation - intrinsic factors
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
Fusion of palatine processes
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
Ectoderm on palatine processes expresses gene (fusion of palatine processes)
Msxl --> genetic cascade releases BMP4 into ectomesenchyme --> ectomesenchyme releases BMP2 --> ectodermal apoptosis
50
Palatine processes fusion complete at
12 weeks
51
Palate 12 weeks -16 weeks
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
Differentiation of bone
Can leave epithelial cell rests
53
Frontonasal process compressed between maxillary processes to form
Protruding nose
54
Fusion of maxillary and mandibular processes to form
Mouth
55
Macrostomia
Maxillary and mandibular processes fail to fuse
56
Clefts
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
Contributory factors of clefts
Heavy smoking Heavy alcohol consumption Folic acid deficiency (in early stages of pregnancy)

Growth and Development (23 decks)

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