Development of the Pharyngeal Apparatus Flashcards

1
Q

What makes up the pharyngeal apparatus?

A

pharyngeal arches, pouches, grooves, and membranes

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2
Q

When do the pharyngeal arches develop?

A

early in the 4th week

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3
Q

What is the first pair of arches known as?

A

the primordial jaws

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4
Q

What initiates the formation of the pharyngeal arches?

A

NCCs migrate away from the dorsal aspect of the developing neural tube and begin to populate ventral areas in what will be the head and neck

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5
Q

Where do cranial neural crest cells migrate from?

A

forebrain, midbrain, and hindbrain regions in the developing neural tube

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6
Q

what are the three main components of the pharyngeal arches?

A

core, external lining, internal lining

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7
Q

what is the core of the pharyngeal arches composed of?

A

mesoderm and mesenchyme

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8
Q

what is the external lining of the pharyngeal arch composed of?

A

ectoderm

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9
Q

what is the internal lining of the pharyngeal arch composed of?

A

endoderm

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10
Q

What is mesenchyme

A

embryonic CT

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11
Q

where does the mesoderm in the core of the pharyngeal arch come from?

A

it arises from paraxial mesoderm

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12
Q

what does the NCC-derived mesenchyme in the pharyngeal arch form?

A

all connective tissue in the head, including the dermis and smooth muscle

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13
Q

what does the paraxial mesoderm in the pharyngeal arch form?

A

forms PA musculature

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14
Q

what does the lateral plate mesoderm in the PA form?

A

angioblasts that differentiate into endothelium

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15
Q

what does prechordal plate mesoderm in the PA form?

A

extraocular musculature

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16
Q

What is the cartilage of the first pharyngeal arch also known as?

A

Meckle’s cartilage

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17
Q

what does the dorsal part of meckle’s cartilage form?

A

malleus and the incus

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18
Q

what does the ventral part of meckle’s cartilage form?

A

primordium of the mandible (like a place holder)

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19
Q

what does the perichondrium of meckle’s cartilage form?

A

anterior ligament of the malleus and the sphenomandibular ligament

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20
Q

what is the cartilage of the 2nd pharyngeal arch also known as?

A

riechert’s cartilage

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21
Q

what does the dorsal part of riechert’s cartilage form?

A

stapes and styloid process o the temporal bone

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22
Q

what does the perichondrium of riechert’s cartilage form?

A

the styloidhyoid ligament

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23
Q

what does the ventral portion of riechert’s cartilage form?

A

It ossifies to form the lesser cornu/horn of the hyoid bone

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24
Q

What does the third pharyngeal arch cartilage form?

A

it ossifies to form the greater cornu/horn of the hyoid bone

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25
Q

what is the body of the hyoid bone formed by?

A

the hypopharyngeal eminence

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26
Q

what does the cartilage of the 4th pharyngeal arch form?

A

laryngeal cartilages including the epiglottis

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27
Q

what does the cartilage of the 6th pharyngeal arch form?

A

laryngeal cartilages

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28
Q

Most muscular components of the face arise from what?

A

paraxial mesoderm

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29
Q

the first pharyngeal arch gives rise to what musculature?

A

muscles of mastication, mylohyoid, anterior belly of the digastric, tensor veli palatini, and tensor tympani

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30
Q

the second pharyngeal arch gives rise to what musculature?

A

stapedius and muscles of facial expression

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31
Q

the third pharyngeal arch gives rise to what musculature?

A

the stylopharyngeus

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32
Q

the fourth pharyngeal arch gives rise to what musculature?

A

cricothyroid and pharyngeal constrictors

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33
Q

the sixth pharyngeal arch gives rise to what musculature?

A

intrinsic muscles of the larynx

34
Q

where do the extraocular muscles arise from?

A

the prechordal plate

35
Q

where does the tongue musculature arise from?

A

the occipital myotomes

36
Q

what nerve supplies the first pharyngeal arch?

A

trigeminal (maxillary and mandibular divisions)

37
Q

what nerve supplies the second pharyngeal arch?

A

facial

38
Q

what nerve supplies the third pharyngeal arch?

A

glossopharyngeal

39
Q

what nerve supplies the 4-6th pharyngeal arch?

A

vagus

40
Q

what are the general signs of a first arch syndrome?

A

malformation of the eyes, ears, mandible, and palate

41
Q

what causes a first arch syndrome?

A

insufficient migration of NCC into the 1st arch during the 4th week of development

42
Q

what is another name for treacher-collins syndrome?

A

mandibulofacial dysostosis

43
Q

what causes treacher-collins syndrome?

A

mutations in TCOF1 gene

44
Q

what does TCOF1 encode for?

A

the protein TREACLE, which is involved in ribosome biogenesis

45
Q

what happens if the TREACLE protein is truncated?

A

there is increased apoptosis of cranial NCCs

46
Q

what is pierre robin sequence associated with?

A

hypoplasia of the mandible, cleft palate, and defects of the eyes and ears

47
Q

what is the initiating defect of pierre robin sequence?

A

small mandible (micrognathia)

48
Q

where are pharyngeal grooves located?

A

externally between pharyngeal arches (covered with ectoderm)

49
Q

where are pharyngeal pouches located?

A

internally as part of the pharynx (covered with endoderm)

50
Q

what does the first pharyngeal groove form?

A

the external acoustic meatus

51
Q

where do grooves 2-4 lie?

A

in the cervical sinus

52
Q

what does the first pharyngeal pouch become?

A

it expands into the tubotympanic recess, which becomes the tympanic cavity and mastoid antrum

53
Q

the tubotympanic recess will eventually elongate into what?

A

the pharyngotympanic tube (auditory tube)

54
Q

what forms the tympanic membrane?

A

the 1st pharyngeal membrane + the intervening mesenchyme

55
Q

what does the second pouch form?

A

tonsillar sinus

56
Q

what does the endoderm of the second sinus form?

A

tonsillar epithelium

57
Q

what does mesenchyme from the second pouch form?

A

lymphoid nodules of palatine tonsil

58
Q

what does the dorsal part of the third pouch become?

A

inferior parathyroid gland

59
Q

what does the ventral part of the third pouch become?

A

thymus

60
Q

where does the third pouch migrate to?

A

caudally (due to growth of brain and cardiac regions)

61
Q

what does the dorsal part of the 4th pouch become?

A

superior parathyroid gland

62
Q

what does the remainder of the 4th pouch become?

A

an ultimobranchial body

63
Q

what happens to the ultimobranchial body?

A

it fuses with the thyroid gland and gives rise to the parafollicular cells

64
Q

how is an external cervical sinus detected?

A

due to discharge of mucus

65
Q

what is an external cervical sinus commonly associated with?

A

auricular sinuses

66
Q

when does the thyroid gland (thyroid primordium) develop?

A

around day 24 of development

67
Q

what does the thyroid primordium form from?

A

an endodermal thickening in the floor of the primordial pharynx

68
Q

how is the thyroid gland connected to the tongue?

A

by a narrow tube known as the thyroglossal duct

69
Q

When will the thyroid primordium become its definitive shape/ when will the thyroglossal duct degenerate?

A

week 7

70
Q

what is mesenchyme derived from?

A

migratory NCCs

71
Q

What kind of mesoderm is located in the core of the pharyngeal arch?

A

paraxial mesoderm (largest contributor), lateral plate mesoderm, and prechordal plate mesoderm

72
Q

What is the hypopharyngeal eminence?

A

a prominence in the floor of the embryonic pharynx (from PA3 and PA4)

73
Q

obstruction of full closure of the palate due to micrognathia leads to what?

A

bilateral cleft palate

74
Q

what is an external cervical sinus?

A

failure of the 2nd groove and cervical sinus to obliterate

75
Q

what is an internal cervical sinus?

A

ingrowth of the 2nd pouch

76
Q

what are remnants of the cervical sinus and/or 2nd groove that get covered with skin?

A

cervical cysts

77
Q

What does an internal cervical sinus open into?

A

tonsillar sinus

78
Q

what is it called when the second pouch remains open out to the second groove and then there is leakage of fluid and other substances that pass through the external opening of the skin?

A

cervical fistula

79
Q

what is it called when the thyroid gland develops but does not descend?

A

sublingual thyroid gland

80
Q

what is DiGeorge syndrome?

A

a breakdown of signaling from PA endoderm to NCC

81
Q

what is not formed in digeorge syndrome?

A

thymus and parathyroid gland