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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
Pharyngeal Arch 3: Muscles
stylopharyngeus
26
Pharyngeal Arch 3: Cranial Nerves
glossopharyngeal nerve (CN IX)
27
Pharyngeal Arch 4: Arch Artery (2)
arch of aorta (left) right subclavian artery (right)
28
Pharyngeal Arch 4: Skeletal Elements
laryngeal cartilages
29
Pharyngeal Arch 4: Muscles (3)
constrictors of pharynx levator veli palatine cricothyroid
30
Pharyngeal Arch 4: Cranial Nerves
superior laryngeal branch of vagus nerve (CN X)
31
Pharyngeal Arch 6: Arch Artery (2)
ductus arteriosus roots of definitive pulmonary arteries
32
Pharyngeal Arch 6: Skeletal Elements
laryngeal cartilages
33
Pharyngeal Arch 6: Muscles
intrinsic muscles of larynx
34
Pharyngeal Arch 6: Cranial Nerves
recurrent laryngeal branch of vagus nerve (CN X)
35
The pharyngeal pouches are lined with
endodermal epithelium, which gives rise to important structures of head/neck
36
The first pharyngeal pouch becomes (2)
tympanic cavity pharyngotympanic (auditory) tube
37
What is the structural function of the pharyngotympanic (auditory) tube?
connects tympanic cavity with pharynx
38
The first pharyngeal membrane becomes
tympanic membrane
39
The first pharyngeal groove becomes
external acoustic meatus (ear canal)
40
The second pharyngeal pouch becomes
the palatine tonsil
41
The caudal part of the third pharyngeal pouch becomes
the bilobed thymus
42
Describe how the third pharyngeal pouch becomes the bilobed thymus.
at week 6, caudal portion of 3rd pharyngeal arch extends ventrally, and then pouches from both sides merge @ ventral midline
43
The cranial part of the third pharyngeal pouch becomes
inferior parathyroid gland
44
The cranial part of the fourth pharyngeal pouch becomes
superior parathyroid gland
45
The caudal part of the fourth pharyngeal pouch becomes
ultimobranchial body, which fuses w/ thyroid gland to become calcitonin-producing parafollicular cells (C cells)
46
The second pharyngeal groove becomes
nothing
47
The third pharyngeal groove becomes
nothing
48
The fourth pharyngeal groove becomes
nothing
49
Describe the fate of the second, third, and fourth pharyngeal grooves.
initially connect to form an opening called a cervical sinus, but then the opening closes up and is obliterated
50
When does the thyroid primordium appear?
day 24
51
Describe the development of the thyroid gland. (4)
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
What is the foramen cecum and where is it located? (2)
opening in dorsum of developing tongue located @ intersection of median sulcus and terminal sulcus of tongue
53
How does the thyroid remain positioned during its descent? How does it remain connected?
during descent, remains positioned _ventrally_ to developing hyoid and laryngeal structures during descent, remains connected to pharynx via _thyroglossal duct_
54
Describe the fate of the thyroglossal duct, the structure that connects the developing thyroid gland to the pharynx.
degenerated by week 7
55
What is the pyramidal lobe?
a remnant of descending thyroid tissue found in about 50% of people
56
What is the purpose of the endoderm of the thyroid primordium?
forms epithelial cords, which merge w/ mesenchyme to form thyroid follicles, which produce thyroid hormones
57
At which point of time is a tongue bud visible?
by the end of week 4
58
Which arch gives rise to the first tongue bud?
first pharyngeal arch
59
Describe how the tongue develops.
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
How is the posterior third of the tongue formed?
from the copula (swelling of 2nd pharyngeal arch) and hypoglossal eminence (swelling of 3rd/4th pharyngeal arches)
61
What is the terminal sulcus?
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
What gives rise to the connective tissue and vasculature of the tongue?
mesenchyme of associated (1st/2nd/3rd/4th) pharyngeal arches
63
What provides sensory innervation to the anterior 2/3 of the tongue?
mandibular division of trigeminal nerve (CN V3)
64
What provides sensory innervation to the posterior 1/3 of the tongue?
glossopharyngeal nerve (CN IX), because posterior 1/3 is mostly derived from 3rd pharyngeal arch
65
The muscles of the tongue are innervated by
the hypoglossal nerve (CN XII)
66
The taste buds of the tongue are innervated by (3)
_branches of:_ facial nerve (CN VII/chorda tympani) glossopharyngeal nerve (CN IX) vagus nerve (CN X)
67
What are ectodermal placodes?
thickenings of the cranial surface ectoderm
68
Ectodermal placodes give rise to (3)
lens of eye (via lens/optic placode) olfactory neurons (via nasal/olfactory placode) otic vesicle of inner ear (via otic/auditory placode)
69
When do ectodermal placodes appear?
by week 4
70
List the five prominences that delineate the stomatodeum (oral primordium) at week 3.
frontonasal prominence (superior) paired maxillary prominences (lateral) paired mandibular prominences (inferior)
71
What is the origin of the maxillary and mandibular prominences that surround the stomatodeum?
first pharyngeal arch
72
Describe how the nostrils form.
thickenings of ectoderm form nasal placodes, which invaginate to form nasal pits, which become nostrils
73
Describe the fate of the frontonasal prominence that originally framed the stomatodeum. (2)
split by nasal pits into 2 medial and 2 lateral nasal prominences also forms forehead + dorsum/apex of nose
74
The lateral nasal prominences give rise to
alae of nose
75
The medial nasal prominences give rise to (4)
nasal septum parts of ethmoid bone cribiform plate part of palate
76
What separates the lateral nasal prominence from the maxillary prominence?
nasolacrimal groove
77
Describe how the nasolacrimal groove gives rise to the nasolacrimal duct and lacrimal sac.
thickened ectoderm at the bottom of the nasolacrimal groove extends upward to form the nasolacrimal duct + lacrimal sac
78
What is the ultimate fate of all the facial prominences?
by week 5, all will fuse and form borders of the mouth
79
Describe how the external ear forms.
_auricular hillocks_ on both sides of first pharyngeal groove fuse to form external ear
80
Describe how the nasopharynx and oropharynx are established.
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
Describe how the conchae form.
elevations on lateral walls of nasal cavity develop into superior/middle/inferior conchae
82
Describe how the paranasal sinuses form.
diverticula from walls of nasal cavity form air-filled extensions, which become paranasal sinuses
83
At which point of time does the primary palate form?
week 6
84
Describe the development of the primary palate. (4)
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
What structure gives rise to the secondary palate?
lateral palatine processes
86
What is the ultimate fate of the primary and secondary palates?
primary and secondary palate fuse, and the fusion area is marked by the incisive foramen
87
Describe how the nasal septum forms.
formed by fusion of medial nasal prominences
88
What happens to the nasal septum in weeks 9-12?
fuses with palatine process
89
Describe how the hard and soft palate form.
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
Describe how the uvula forms. (2)
forms along with soft palate (same process) from posterior portion of lateral palatine process (do not ossify)
91
List the anomalies associated exclusively with the first pharyngeal arch.
Treacher Collins syndrome Pierre Robin sequence
92
What is Treacher Collins syndrome?
genetic disorder in which migration of neural crest cells into 1st pharyngeal arch is inhibited
93
What are three clinical features of Treacher Collins syndrome?
hypoplasia of mandible and zygomatic bones external ear abnormalities lower eyelid abnormalities
94
What happens in Pierre Robinson sequence? (2)
underdeveloped jaw interferes with tongue descent, causing cleft soft plate and small tongue airway is restricted
95
What are two anomalies associated with both the first and second pharyngeal arches?
hemifacial microsomia Goldenhar syndrome
96
What is hemifacial microsomia?
syndrome of small jaw and external ear anomalies
97
How does hemifacial microsomia occur?
inappropriate vascularization of developing structures
98
What is Goldenhar syndrome?
similar to hemifacial microsomia, plus anomalies of eyes, vertebral column, heart, and urinary tract
99
What is an anomaly associated with several pharyngeal arches?
DiGeorge anomaly
100
What is DiGeorge anomaly?
failure of differentiation of 3rd/4th pharyngeal pouches
101
What are the symptoms of DiGeorge anomaly? (4)
hypoparathyroidism hypocalcemia absent thymus = immune defects interrupted aortic arch
102
What causes DiGeorge anomaly? (2)
sporadic disorder deletion of chromosome band 22q11
103
List three thyroid anomalies.
congenital hypothyroidism thyroglossal duct cysts ectopic thyroid glands
104
How do thyroglossal duct cysts form?
form when the thyroglossal duct doesn't degenerate like it's supposed to, but persists
105
Where are thyroglossal duct cysts usually located?
located in tongue or ventral region of neck
106
What happens if a thyroglossal duct cyst — normally benign — gets infected?
can lead to a perforation of skin, called a thyroglossal sinus
107
Where are ectopic thyroid glands typically found?
found along course of thyroglossal duct
108
What is the most common form of ectopic thyroid tissue?
lingual thyroid tissue at back of tongue
109
How do pharyngeal cysts form?
when parts of pharyngeal grooves 2/3/4 don't degenerate

Human Structure - Block 2 (22 decks)

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