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Development Of The Pharyngeal Apparatus Flashcards

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1
Q

Which structures make up the pharyngeal apparatus?

A

Pharyngeal arches (PA), pouches, grooves (clefts) and membranes

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2
Q

What does the pharyngeal apparatus contribute to?

A

Formation of nasal cavities, oral cavity, tongue, larynx, pharynx, ear and neck

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3
Q

When do pharyngeal arches develop?

A

Early in the 4th week as neural crest cells that migrate into the future head and neck

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4
Q

Explain the appearance of the 1st-6th PAs

A

1st pair (primordial jaws) appear lateral to developing pharynx
Arches 2-4 soon appear as ridges on each side of the future head and neck regions
5/6th arches are rudimentary and not visible on the surface of the embryo

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5
Q

Neural crest cells migrate from which structures?

A

Forebrain, midbrain and hindbrain (during the 4th week)

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6
Q

What does each PA consist of?

A

A core of mesoderm and mesenchyme

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7
Q

Each PA is covered by what?

A

Externally by ectoderm and internally by endoderm

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8
Q

What is mesenchyme?

A

Embryonic CT derived from migratory NCC

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9
Q

What is head mesoderm?

A

Mesoderm arising from paraxial mesoderm

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10
Q

Once formed the pharyngeal arches support and give rise to what?

A

Support the lateral walls of the primitive pharynx

Give rise to facial prominences that contribute to craniofacial mesoderm

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11
Q

What is the stomodeum?

A

Oral cavity

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12
Q

What are the 4 components of a pharyngeal arch?

A

NCC-derived mesenchyme, paraxial mesoderm, lateral plate mesoderm and prechordal plate mesoderm

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13
Q

What does NCC-derived mesenchyme form?

A

Forms all CT in the head including the dermis and smooth muscle

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14
Q

What is the function of paraxial mesoderm in PAs?

A

Populates each arch to form PA musculature

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15
Q

What is the function of lateral plate mesoderm within PAs?

A

Angioblasts differentiate into endothelium

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16
Q

What does the prechordal plate mesoderm form within the PAs?

A

Extraocular musculature

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17
Q

What role does pharyngeal endoderm play?

A

Plays an essential role in regulating the development of the PA

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18
Q

What are the 4 elements that the PA house?

A

Cartilaginous rods, muscular component, CNs and arch artery

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19
Q

What does the cartilaginous rod of the PAs form?

A

Skeletal elements

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20
Q

What does the muscular component of a PA form?

A

Muscles of the head/neck

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21
Q

The CNs in PA have what components?

A

Sensory and/or motor components

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22
Q

What does the arch artery within the PA form?

A

Vasculature of the head/neck

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23
Q

What is Meckel’s cartilage?

A

Cartilage of the 1st PA

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24
Q

The dorsal portion of the Meckel’s cartilage forms what?

A

Malleus and incus

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25
Describe Meckel’s cartilage
Bone forms laterally to Meckel’s which disintegrates
26
What does the ventral part of Meckel’s cartilage form?
The primordium of the mandible
27
What does the perichondrium of Meckel’s cartilage give rise to?
Anterior ligament of malleus and sphenomandibular L
28
What is Rierchert’s cartilage?
Cartilage of PA2
29
What does the dorsal region of Riechert’s cartilage contribute to?
Stapes and styloid of the temporal bone, remainder disintegrates
30
What does the perichondrium of Riechert’s cartilage form?
Stylohyoid ligament
31
What does the ventral portion of Riechert’s cartilage form after ossification?
Lesser Cornu/horn of hyoid bone
32
What does the third arch cartilage become after it ossifies?
Forms greater Cornu of hyoid bone
33
The body of the hyoid bone is formed by what?
Hypopharyngeal eminence | Prominence in floor of embryonic pharynx (from PA3 and 4)
34
What does the 4th arch cartilage give rise to?
Laryngeal cartilages, including the epiglottis (NCC derived)
35
What does the 6th PA cartilage give rise to?
Laryngeal cartilages but origin is uncertain
36
Most muscular components of the PAs are derived from what?
Paraxial mesoderm
37
What are the muscular components of the first PA?
Muscles of mastication, mylohyoid, anterior belly of digastric, tensor tympani and tensor veli palatini (CN V)
38
What are the muscular components of the second PA?
Muscles of facial expression (CN VII) | Posterior belly of digastric, stylohyoid and stapedius
39
What are the muscular components of the 3rd PA?
Stylopharyngeus M (CN IX)
40
What are the muscular components of the 4th PA?
Cricothyroid, levator veli palatini and pharyngeal constrictors (CN X)
41
What are the muscular components of the 6th PA?
Intrinsic muscles of the larynx except for the cricothyroid | CN X
42
What do extraocular muscles arise from?
Prechordal plate Includes levator palpebrae superioris, superior, medial and inferior rectus, inferior oblique, superior oblique and lateral rectus
43
What does tongue musculature arise from?
Occipital myotomes
44
What does the trigeminal nerve (CN V) supply?
The first PA Principal sensory nerve of the head and neck Motor nerve for the muscles of mastication
45
What does the facial nerve (CN VII) supply?
Second PA (muscles of facial expression)
46
What does the glossopharyngeal nerve (CN IX) supply?
3rd PA (stylopharyngeus M)
47
What does the vagus nerve (CN X) supply?
4th-6th PA 4th arch -> supplied by superior laryngeal 6th arch -> supplied by recurrent laryngeal branches of CN X Constrictors of pharynx (4th) and intrinsic muscles of larynx (6th)
48
What is first arch syndrome?
Abnormal development of the components of the first arch Malformation of the eyes, mandible and palate Results from insufficient migration of NCC into the 1st PA during the 4th week
49
What is Treacher-Collins syndrome (mandibulofacial dysostosis?
Malar hypoplasia w/ down-slanting palpebral fissures, defects of lower eyelids, deformed external ears and sometimes middle and internal ears
50
Explain the genetics of Treacher-Collins syndrome
Autosomal dominant disorder caused by mutation in Treacher-Collins-Franseschetti syndrome 1 gene (TCOF1) which encodes for the protein TREACLE invovled in ribosome biogenesis Truncated protein leading to increased apoptosis of cranial NCC
51
What are two conditions that are an example of first arch syndrome?
Treacher-Collins syndrome and Pierre Robin sequence
52
What is Pierre Robin sequence?
Occurs de novo in most pts | Associated with hypoplasia of the mandible, cleft palate and defects of the eyes and ears
53
Explain the defect in Pierre Robin and how it leads to cleft palate
Initiating defect is a small mandible (micrognathia) -> results in posterior displacement of the tongue -> obstruction of full closure of the palate -> results in bilateral cleft palate
54
Where are pharyngeal grooves located?
Externally between pharyngeal arches covered with ectoderm
55
Where are pharyngeal pouches located?
Internally as part of the pharynx covered with endoderm | 1st pair lies between the 1st and 2nd arches
56
Where are pharyngeal membranes located?
Between the pharyngeal grooves and pouches
57
What will the 1st pharyngeal groove form?
The external acoustic meatus
58
Where do grooves 2-4 lie?
In the cervical sinus which is eventually obliterated
59
Birth defects in which groove are common?
In the 2nd groove
60
The 1st pouch expands into the tubotympanic recess which becomes what?
Tympanic cavity and mastoid antrum
61
The 1st pouch also elongates to form what?
Pharyngotympanic tube
62
The endoderm of the 1st pouch contacts what structure?
The 1st pharyngeal groove and contributes to the tympanic membrane
63
What forms the tympanic membrane?
1st membrane + intervening mesenchyme
64
What does the 2nd pouch form?
Portion of it forms tonsillar sinus Endoderm will form tonsillar epithelium Mesenchyme will form lymphoid nodules of palatine tonsils
65
What does the 3rd pouch form?
Dorsal portion differentiates into inferior parathyroid gland Ventral portion forms the thymus Both migrate caudally due to growth of brain and cardiac regions
66
What are examples of branchial anomalies?
External and internal cervical sinus, cervical cysts and cervical fistula
67
What is external cervical sinus?
Failure of the 2nd groove and cervical sinus to obliterate Typically external (internal is rare) Detected due to discharge of mucus Commonly associated with auricular sinuses
68
What is internal cervical sinus?
Persistence of the 2nd pouch Rare Open into tonsillar sinus or near palatopharyngeal arch
69
What does the 4th pouch form?
Dorsal portion differentiates into superior parathyroid glands Remainder forms the ultimobranchial body which fuses with thyroid gland and gives rise to parafollicular cells
70
What are cervical cysts?
Remnants of cervical conus and/or 2nd groove Slowly enlarging, painless, free-lying cyst in the neck, inferior to the angle of the mandible Accumulation of fluid and cellular debris occurs
71
What is a cervical fistula?
Canal that opens into tonsillar sinus and external side of the neck Persistence of parts of the 2nd groove and pouch Ascends through subcutaneous tissue and platysma to reach the carotid sheath -> Passes between carotids and opens into tonsillar sinus
72
What is the first endocrine gland to develop?
Thyroid primordium (~24 dpf) and forms from an endodermal thickening in the floor of the primordial pharynx
73
As the tongue grows what structure descends into the neck?
The thyroid primordium and moves ventral to the hyoid bone and laryngeal cartilages
74
The thyroid primordium is connected to the tongue by what?
A narrow tube called the thyroglossal duct
75
Describe the development of the thyroid gland
Thyroid primordium is hollow but will become a solid cellular mass Divides into right/left lobes connected by the isthmus Definitive shape by 7 weeks and thryoglossal duct will degenerate
76
What anomalies are associated with thyroid gland development?
Ectopic thyroid tissue (accessory, lingual and cervical), sublingual thyroid gland and thyroglossal duct cyst Congenital: Agenesis of the thyroid gland, thyroid hemiagenesis and DiGeorge syndrome
77
What is ectopic thyroid tissue?
Can form along the course of the duct | Can be accessory, lingual or cervical
78
What is a sublingual thyroid gland?
Gland forms but does not descend in the neck
79
What is a thyroglossal duct cyst?
Forms in the tongue or anterior neck | Critical to distinguish from ectopic thyroid prior to surgical removal
80
What is agenesis of the thyroid gland?
Absence of a thyroid gland or one of its lobes (rare)
81
What is thyroid hemiagenesis?
Unilateral failure of formation Left lobe is more commonly absent Mutations in the receptor for thyroid-stimulating hormone (TSH) are likely involved
82
What is DiGeorge syndrome?
Breakdown of signaling from PA endoderm to NCC Agenesis of thymus and parathyroid glands Develop congenital hypoparathyroidism
83
What are characteristics of DiGeorge syndrome?
Shortened philtrum of upper lip, low set and notched ears Nasal clefts and thyroid hypoplasia Cardiac abnormalities (defects in the aortic arch and heart)

NE Exam 1 (20 decks)

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