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Human Structure - Block 2 > Embryology 4 > Flashcards

Embryology 4 Flashcards

1
Q

What are the four components of the pharyngeal apparatus?

A

pharyngeal arches

pharyngeal pouches

pharyngeal grooves

pharyngeal membranes

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2
Q

In humans, which pharyngeal arches develop?

A

1, 2, 3, 4, 6 (rudimentary)

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3
Q

At which point of time do the four primary pairs of pharyngeal arches become visible?

A

at the end of week 4

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4
Q

Describe how the pharyngeal arches are separated.

A

indented on the outside by pharyngeal grooves

indented on the inside by pharyngeal pouches

grooves and pouches separated by pharyngeal membrane (two-layered)

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5
Q

The pharynx is separated from the amniotic cavity by

A

the oropharyngeal membrane

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6
Q

How does the oropharyngeal membrane form?

A

forms from prechordal plate duing week 3 of gastrulation

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7
Q

What is the stomatodeum?

A

primitive mouth, which forms by day 26

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8
Q

Eventually, how does the primitive pharynx (formed by the pharyngeal arches) become connected to the amniotic cavity?

A

rupturing of oropharyngeal membrane

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9
Q

The mesenchyme core of the pharyngeal membranes is derived from

A

the paraxial and lateral mesoderm

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10
Q

What is ectomesenchyme and how does it form?

A

ectomesenchyme = prominent mesenchymal tissue of head/neck

forms when neural crest cells in week 4 migrate to pharyngeal arches and merge w/ mesoderm

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11
Q

Compare the contributions of the ectomesenchyme and the original paraxial/lateral mesoderm.

A

ectomesenchyme = contributes to bones/connective tissue of head/neck

original paraxial/lateral mesoderm = skeletal musculature + blood vessels

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12
Q

What is the composition of a typical pharyngeal arch?

A

blood vessel (called an aortic arch)

cartilage rod

muscle component

nerve (both motor and sensory functions)

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13
Q

The nerves of pharyngeal arches are specifically known as

A

cranial nerves

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14
Q

Cranial nerves (which are the nerves of the pharnygeal arches) derive from what structure?

A

derive from neuroectoderm of primitive brain

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15
Q

Pharyngeal Arch 1: Arch Artery

A

terminal branch of maxillary artery

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16
Q

Pharyngeal Arch 1: Skeletal Elements (7)

A

from endochondral ossification:

incus

malleus

part of sphenoid

from mesenchyme membranous ossification:

maxilla

zygomatic bone

squamous part of temporal bone

mandible

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17
Q

Pharyngeal Arch 1: Muscles (5)

A

mastication muscles

mylohyoid

anterior belly of digastric

tensor tympani

tensor veli palatini

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18
Q

Pharyngeal Arch 1: Cranial Nerves

A

maxillary (V2) and mandibular (V3) portions of trigeminal nerve (CN V)

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19
Q

Pharyngeal Arch 2: Arch Artery

A

stapedial artery (in embryo)

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20
Q

Pharyngeal Arch 2: Skeletal Elements (3)

A

from endochondral ossification:

stapes

styloid process

part of hyoid

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21
Q

Pharyngeal Arch 2: Muscles (4)

A

facial expression

posterior belly of digastric

stylohyoid

stapedius

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22
Q

Pharyngeal Arch 2: Cranial Nerves

A

facial nerve (CN VII)

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23
Q

Pharyngeal Arch 3: Arch Artery (2)

A

common carotid artery

root of internal carotid artery

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24
Q

Pharyngeal Arch 3: Skeletal Elements

A

from endochondral ossification:

parts of hyoid

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25
Q

Pharyngeal Arch 3: Muscles

A

stylopharyngeus

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26
Q

Pharyngeal Arch 3: Cranial Nerves

A

glossopharyngeal nerve (CN IX)

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27
Q

Pharyngeal Arch 4: Arch Artery (2)

A

arch of aorta (left)

right subclavian artery (right)

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28
Q

Pharyngeal Arch 4: Skeletal Elements

A

laryngeal cartilages

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29
Q

Pharyngeal Arch 4: Muscles (3)

A

constrictors of pharynx

levator veli palatine

cricothyroid

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30
Q

Pharyngeal Arch 4: Cranial Nerves

A

superior laryngeal branch of vagus nerve (CN X)

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31
Q

Pharyngeal Arch 6: Arch Artery (2)

A

ductus arteriosus

roots of definitive pulmonary arteries

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32
Q

Pharyngeal Arch 6: Skeletal Elements

A

laryngeal cartilages

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33
Q

Pharyngeal Arch 6: Muscles

A

intrinsic muscles of larynx

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34
Q

Pharyngeal Arch 6: Cranial Nerves

A

recurrent laryngeal branch of vagus nerve (CN X)

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35
Q

The pharyngeal pouches are lined with

A

endodermal epithelium, which gives rise to important structures of head/neck

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36
Q

The first pharyngeal pouch becomes (2)

A

tympanic cavity

pharyngotympanic (auditory) tube

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37
Q

What is the structural function of the pharyngotympanic (auditory) tube?

A

connects tympanic cavity with pharynx

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38
Q

The first pharyngeal membrane becomes

A

tympanic membrane

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39
Q

The first pharyngeal groove becomes

A

external acoustic meatus (ear canal)

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40
Q

The second pharyngeal pouch becomes

A

the palatine tonsil

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41
Q

The caudal part of the third pharyngeal pouch becomes

A

the bilobed thymus

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42
Q

Describe how the third pharyngeal pouch becomes the bilobed thymus.

A

at week 6, caudal portion of 3rd pharyngeal arch extends ventrally, and then pouches from both sides merge @ ventral midline

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43
Q

The cranial part of the third pharyngeal pouch becomes

A

inferior parathyroid gland

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44
Q

The cranial part of the fourth pharyngeal pouch becomes

A

superior parathyroid gland

45
Q

The caudal part of the fourth pharyngeal pouch becomes

A

ultimobranchial body, which fuses w/ thyroid gland to become calcitonin-producing parafollicular cells (C cells)

46
Q

The second pharyngeal groove becomes

A

nothing

47
Q

The third pharyngeal groove becomes

A

nothing

48
Q

The fourth pharyngeal groove becomes

A

nothing

49
Q

Describe the fate of the second, third, and fourth pharyngeal grooves.

A

initially connect to form an opening called a cervical sinus, but then the opening closes up and is obliterated

50
Q

When does the thyroid primordium appear?

A

day 24

51
Q

Describe the development of the thyroid gland. (4)

A

thyroid primordium migrates caudally into neck via foramen cecum

ventral part becomes bilobed thyroid gland

completely formed by week 7

reaches final position inferior to larynx and antero-lateral to trachea

52
Q

What is the foramen cecum and where is it located? (2)

A

opening in dorsum of developing tongue

located @ intersection of median sulcus and terminal sulcus of tongue

53
Q

How does the thyroid remain positioned during its descent? How does it remain connected?

A

during descent, remains positioned ventrally to developing hyoid and laryngeal structures

during descent, remains connected to pharynx via thyroglossal duct

54
Q

Describe the fate of the thyroglossal duct, the structure that connects the developing thyroid gland to the pharynx.

A

degenerated by week 7

55
Q

What is the pyramidal lobe?

A

a remnant of descending thyroid tissue found in about 50% of people

56
Q

What is the purpose of the endoderm of the thyroid primordium?

A

forms epithelial cords, which merge w/ mesenchyme to form thyroid follicles, which produce thyroid hormones

57
Q

At which point of time is a tongue bud visible?

A

by the end of week 4

58
Q

Which arch gives rise to the first tongue bud?

A

first pharyngeal arch

59
Q

Describe how the tongue develops.

A

median tongue bud appears first, but then lateral buds grow/fuse/take over the median bud and ultimately form the anterior 2/3 of the tongue

60
Q

How is the posterior third of the tongue formed?

A

from the copula (swelling of 2nd pharyngeal arch) and hypoglossal eminence (swelling of 3rd/4th pharyngeal arches)

61
Q

What is the terminal sulcus?

A

line of fusion b/w anterior 2/3 (i.e. 1st pharyngeal arch) and posterior 1/3 (i.e. 2nd/3rd/4th pharyngeal arches) of tongue

62
Q

What gives rise to the connective tissue and vasculature of the tongue?

A

mesenchyme of associated (1st/2nd/3rd/4th) pharyngeal arches

63
Q

What provides sensory innervation to the anterior 2/3 of the tongue?

A

mandibular division of trigeminal nerve (CN V3)

64
Q

What provides sensory innervation to the posterior 1/3 of the tongue?

A

glossopharyngeal nerve (CN IX), because posterior 1/3 is mostly derived from 3rd pharyngeal arch

65
Q

The muscles of the tongue are innervated by

A

the hypoglossal nerve (CN XII)

66
Q

The taste buds of the tongue are innervated by (3)

A

branches of:

facial nerve (CN VII/chorda tympani)

glossopharyngeal nerve (CN IX)

vagus nerve (CN X)

67
Q

What are ectodermal placodes?

A

thickenings of the cranial surface ectoderm

68
Q

Ectodermal placodes give rise to (3)

A

lens of eye (via lens/optic placode)

olfactory neurons (via nasal/olfactory placode)

otic vesicle of inner ear (via otic/auditory placode)

69
Q

When do ectodermal placodes appear?

A

by week 4

70
Q

List the five prominences that delineate the stomatodeum (oral primordium) at week 3.

A

frontonasal prominence (superior)

paired maxillary prominences (lateral)

paired mandibular prominences (inferior)

71
Q

What is the origin of the maxillary and mandibular prominences that surround the stomatodeum?

A

first pharyngeal arch

72
Q

Describe how the nostrils form.

A

thickenings of ectoderm form nasal placodes, which invaginate to form nasal pits, which become nostrils

73
Q

Describe the fate of the frontonasal prominence that originally framed the stomatodeum. (2)

A

split by nasal pits into 2 medial and 2 lateral nasal prominences

also forms forehead + dorsum/apex of nose

74
Q

The lateral nasal prominences give rise to

A

alae of nose

75
Q

The medial nasal prominences give rise to (4)

A

nasal septum

parts of ethmoid bone

cribiform plate

part of palate

76
Q

What separates the lateral nasal prominence from the maxillary prominence?

A

nasolacrimal groove

77
Q

Describe how the nasolacrimal groove gives rise to the nasolacrimal duct and lacrimal sac.

A

thickened ectoderm at the bottom of the nasolacrimal groove extends upward to form the nasolacrimal duct + lacrimal sac

78
Q

What is the ultimate fate of all the facial prominences?

A

by week 5, all will fuse and form borders of the mouth

79
Q

Describe how the external ear forms.

A

auricular hillocks on both sides of first pharyngeal groove fuse to form external ear

80
Q

Describe how the nasopharynx and oropharynx are established.

A

nasal pits deepen to form nasal sacs, which are initially separated from oral cavity by oronasal membrane, but membrane breaks down to establish nasal-oral connection

81
Q

Describe how the conchae form.

A

elevations on lateral walls of nasal cavity develop into superior/middle/inferior conchae

82
Q

Describe how the paranasal sinuses form.

A

diverticula from walls of nasal cavity form air-filled extensions, which become paranasal sinuses

83
Q

At which point of time does the primary palate form?

A

week 6

84
Q

Describe the development of the primary palate. (4)

A

formed in week 6 by fusion of medial nasal prominences

primary palate then fuses with maxillary prominences

becomes premaxillary part of maxilla

comprises anterior portion of adult hard palate

85
Q

What structure gives rise to the secondary palate?

A

lateral palatine processes

86
Q

What is the ultimate fate of the primary and secondary palates?

A

primary and secondary palate fuse, and the fusion area is marked by the incisive foramen

87
Q

Describe how the nasal septum forms.

A

formed by fusion of medial nasal prominences

88
Q

What happens to the nasal septum in weeks 9-12?

A

fuses with palatine process

89
Q

Describe how the hard and soft palate form.

A

hard palate = formed by build up of bone tissue in primary palate + anterior portion of lateral palatine process

soft palate = from posterior portion of lateral palatine process (do not ossify)

90
Q

Describe how the uvula forms. (2)

A

forms along with soft palate (same process)

from posterior portion of lateral palatine process (do not ossify)

91
Q

List the anomalies associated exclusively with the first pharyngeal arch.

A

Treacher Collins syndrome

Pierre Robin sequence

92
Q

What is Treacher Collins syndrome?

A

genetic disorder in which migration of neural crest cells into 1st pharyngeal arch is inhibited

93
Q

What are three clinical features of Treacher Collins syndrome?

A

hypoplasia of mandible and zygomatic bones

external ear abnormalities

lower eyelid abnormalities

94
Q

What happens in Pierre Robinson sequence? (2)

A

underdeveloped jaw interferes with tongue descent, causing cleft soft plate and small tongue

airway is restricted

95
Q

What are two anomalies associated with both the first and second pharyngeal arches?

A

hemifacial microsomia

Goldenhar syndrome

96
Q

What is hemifacial microsomia?

A

syndrome of small jaw and external ear anomalies

97
Q

How does hemifacial microsomia occur?

A

inappropriate vascularization of developing structures

98
Q

What is Goldenhar syndrome?

A

similar to hemifacial microsomia, plus anomalies of eyes, vertebral column, heart, and urinary tract

99
Q

What is an anomaly associated with several pharyngeal arches?

A

DiGeorge anomaly

100
Q

What is DiGeorge anomaly?

A

failure of differentiation of 3rd/4th pharyngeal pouches

101
Q

What are the symptoms of DiGeorge anomaly? (4)

A

hypoparathyroidism

hypocalcemia

absent thymus = immune defects

interrupted aortic arch

102
Q

What causes DiGeorge anomaly? (2)

A

sporadic disorder

deletion of chromosome band 22q11

103
Q

List three thyroid anomalies.

A

congenital hypothyroidism

thyroglossal duct cysts

ectopic thyroid glands

104
Q

How do thyroglossal duct cysts form?

A

form when the thyroglossal duct doesn’t degenerate like it’s supposed to, but persists

105
Q

Where are thyroglossal duct cysts usually located?

A

located in tongue or ventral region of neck

106
Q

What happens if a thyroglossal duct cyst — normally benign — gets infected?

A

can lead to a perforation of skin, called a thyroglossal sinus

107
Q

Where are ectopic thyroid glands typically found?

A

found along course of thyroglossal duct

108
Q

What is the most common form of ectopic thyroid tissue?

A

lingual thyroid tissue at back of tongue

109
Q

How do pharyngeal cysts form?

A

when parts of pharyngeal grooves 2/3/4 don’t degenerate

Human Structure - Block 2 (22 decks)

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