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NS-1 > Development of the Pharyngeal Arches > Flashcards

Development of the Pharyngeal Arches Flashcards

1
Q

What makes up the pharyngeal apparatus?

A

pharyngeal arches

pouches

grooves (clefts)

membranes

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2
Q

When do the pharyngeal arches develop?

What are they made of?

A

early in 4th week

NCCs migrating into the future head and neck

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3
Q

which areches are visible on the embryo surface and where are they?

A

2-4 appear as ridges on each side of the future head and neck

5 and 6 not visible on surface

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4
Q

Where do the NCCs that make up the arches come from?

A

rhombomeres from hindbrain

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5
Q

What rhombomeres contribute to each PA?

A

R1-2 –> PA1

R4 –> PA2

R6-7 –> PA3/4

(R3 and 5 produce few NCC)

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6
Q

What types of tissue make up each pharyngeal arch?

A

core of mesenchyme = NC

ectoderm on outside

endoderm on inside

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7
Q

What does the first arch separate into?

A

maxillary and mandibular prominences

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8
Q

When and how does the cervical sinus form and disappear?

A

5th week: PA2 overgrows 3 and 4 –> cervical sinus = ectodermal depression –> end of 7th week, disappears

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9
Q

What does the NC in the arches form?

A

all connective tissue

bone

dermis

smooth muscle

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10
Q

What type of mesoderm contributes to the arches and what does it form?

A

paraxial

muscle primordium (skeletal)

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11
Q

What from the arches forms endothelium?

A

lateral plate angioblasts

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12
Q

What does pharyngeal endoderm do?

A

plays role in regulated arch development

forms glands, ear

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13
Q

What does the artery in an arch arise from?

A

truncus arteriosus –> passes around primordial pharynx to enter dorsal aorta

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14
Q

What are the 4 main structures within a pharyngeal arch?

A

artery from truncus arteriosus

cartilagious rod (will make skeleton)

muscle from paraxial meso

nerve from ecto

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15
Q

what are the nerves in arches derived from and what do they supply?

A

derived from developing brain

supply mucosa and muscles derived from each arch

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16
Q

What nerve is associated with PA1?

A

trigeminal N = V

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17
Q

What nerve is associated with PA2?

A

CN 7 = Facial N

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18
Q

What nerve is associated with PA3?

A

Glossopharyngeal N = 9

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19
Q

What nerve is associated with PA4?

A

Superior laryngeal branch of Vagus n (10)

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20
Q

What nerve is associated with PA6?

A

Recurrent laryngeal branch of vagus n (10)

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21
Q

What muscles and ligaments originate from PA1?

A

ms of mastication

mylohyoid, ant belly of digastric, *tensor tympani, tensor veli palatini

Anterior L of malleus

Spheno-andibular L

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22
Q

What muscles and ligaments originate from PA2?

A

Muscles of facial expression

posterior belly of the digastric, stylohyoid, stapedius

stylohyoid L

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23
Q

What muscle originiate from PA3?

A

Stylopharyngeus

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24
Q

What muscles originiate from PA4?

A

Constrictors of pharynx

cricothyroid

lavator veli palatini

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25
What muscles originiate from PA6?
Intrinisc ms of larynx \*except cricothyroid\*
26
What is Meckel's cartilage?
cartilage of PA1 dorsal nodules --\> form malleus and incus perichondrium --\> ant L of malleus and sphenomandibular L ventral parts --\> mandible
27
what is Riechert's cartilage and what does it form?
cartilage of **PA2** Reichert's + dorsal anlage --\> **stapes** and **styloid process** of temporal bone also forms **stylohyoid L** ventral end --\> **lesser horn** of hyoid bone
28
How does the stylohyoid L form?
cartilage of PA2 (reichert's) btw styloid and hyoid regresses --\> perichondrium forms stylohyoid L
29
What do the greater and lesser horns of the hyoid bone arise from?
Lesser = from Reichert's cartilage of PA2 greater = from third arch cartilage
30
What does the third arch cartilage form?
greater horn of of hyoid bone contributes to body of hyoid bone
31
What forms the body of hyoid bone?
hypopharyngeal eminence = prominence in floor of embryo pharynx from 3 and 4 --\> body of hyoid bone
32
What forms from the 4th and 6th arch cartilages?
fuse --\> laryngeal cartilages (except epiglottis) (5th arch, if present, is rudimentary and has no derivatives)
33
What are the pharyngeal arch muscles derived from?
paraxial mesoderm and prechordal plate
34
what types of nerves supply the dermis and mucous membranes of the head and neck?
special visceral afferents
35
What are the arteries of the 3rd arch?
common and internal carotids
36
What does the distal internal carotid a form from?
extensions of dorsal aorta
37
How do the external carotid As form?
de nove from common carotids
38
where are the 1st pair of pharyngeal pouches? How many are there total?
1st pair btw 1st and second arches (internal, lined w/ endoderm) 5 pairs total
39
What are the pharyngeal membranes?
where the pouch endoderm contacts ectoderm of pharyngeal grooves (separates pouch from groove)
40
What forms the tympanic membrane?
1st pharyngeal membrane + intervening mesenchyme (endo + NC + ecto)
41
What does the 1st pharyngeal pouch form?
expands --\> tupotympanic recess --\> distal part contributes to tympanic membrane cavity of recess --\> tympanic cavity and mastoid antrum connection of recess w/ pharynx elongates --\> pharyngotympanic tube
42
What does the 2nd pharyngeal pouch form (in general)?
largely obliterated as palatine tonsil forms part of pouch --\> **tonsillar sinus** = depression btw palatoglossal and palatopharyngeal arches
43
What does the endoderm of the second pouch form?
proliferates --\> central core breaks down --\> tonsillar crypts (remainder of endo forms epithelium of tonsils and lining of crypts)
44
What does the mesenchyme of the second pouch form?
around tonsillar crypts (endoderm) --\> turns into **lymphoid tissue at 20 weeks** will form lymphatic nodules of **palatine tonsil**
45
What does the 3rd pharyngeal pouch form?
dorsal part = solid, bulbar --\> 6th week: **inferior parathyroid gland** ventral part = elongated and hollow --\> proliferates and obliterates cavities --\> forms thymus
46
What occurs to the location of derivatives of 2nd-4th pouches?
glands lose connections w/ pharynx due to growth of brain and heart --\> caudally displaced
47
What do the parathyroid glands develop from?
4th pouch --\> superior glands 3rd pouch --\> inferior glands
48
What does the 4th pharyngeal pouch form?
dorsal, bulbar part: epithelium --\> **superior parathyroid gland** elongated, ventral part
49
What are pharyngeal grooves?
separate arches externally = ectoderm 1-4 arise duing 4th and 5th weeks
50
What do the 1st pharyngeal grooves form?
persist as external auditory meatus
51
What do pharyngeal grooves 2-4 form?
form cervical sinus --\> obliterated 7th week defects of 2nd groove are common
52
what are cervical/branchial cysts?
remnants of cervical sinus/2nd groove --\> spherical/elongated cyst often freely mobile, inferior to angle of mandible or on anterior border of SCM apparent until late childhood/early adulthood fluid and cellular debris from desquamation of epithelial lining
53
How does the thyroid gland develop?
1st endocrine gland to develop (24 dpf) --\> thyroid primordium median endodermal thickening in floor of primordial pharynx --\> descends in neck w/ tongue and passes ventral to hyoid bone connected to tungue by **thyroglossal duct**
54
What occurs at 7 weeks of thyroid gland development?
solid mass of endodermal cells --\> broken into epithelial cords by vascular mesenchyme thyroglossal duct has degenerated proximal opening of duct persists as **foramen cecum** on tongue
55
What is the pyramidal lobe of the thyroid?
lobe extending superiorly from isthmus persists in ~50% of people
56
What occurs at 10 weeks of thyroid gland development?
cords divided into cellular groups and a lumen cells in single layer around follicles
57
What occurs at 11 weeks of thyroid gland development?
colloid appears and synthesis of TH starts
58
What occurs at 20 weeks of thyroid gland development?
levels of fetal TSH and thyroxine increase
59
What occurs at 35 weeks of thyroid gland development?
fetal TSH adn thyroxine reach adult levels
60
What is the ultimopharyngeal body?
elongated ventral part of 4th pouches --\> fuse with thyroid gland form **parafollicular cells (NC derived)** --\> calcitonin
61
When do the parathyroid glands form?
5th week: epithelium of 3rd and 4th pouches contributing to glands proliferates --\> vascular mesenchyme invades chief cells dev in embryo oxyphil cells diff at 5-7 yrs
62
How do the cells of the thymus develop?
from 3rd pouches --\> epithelial tubes grow into mesenchyme and become solid cords that proliferate and form side branches each side branch --\> core of a lobule some cords become arranged around central point = **thymic corpuscles** other cords --\> **epithelial reticulum** lymphocytes invade reticulum
63
What is first arch syndrome?
abnormal dev of first arch --\> malformation of eyes, ears, mandible, and palate insufficient NCC migration during 4th week
64
What is Treacher-Collins syndrome?
mandibulofacial dysostosis AD inheritance: mutations in **TCOF1** --\> malformed **TREACLE** protein --\> **ribosomes** not formed right in NCCs --\> proteins not formed right --\> increased a**poptosis of cranial NCC** molar hypoplasia w/ down-slanting palpebral fissures, other face defects form of 1st pharyngeal arch syndrome
65
what is Pierre Robin sequence?
type of 1st arch syndrome typically occurs de novo hypoplasia of mandible, cleft palate, eye and ear defects initiating defect is small mandible --\> posterior tongue displacement --\> obstructs full palate closure --\> bilateral cleft palate
66
What is micrognathia?
small mandible see in Pierre Robin sequence
67
Is it more common to have extra thyroid tissue or agenesis?
extra tissue
68
What is agenesis of thyroid gland? Hemiagenesis?
agenesis = absence of gland or one lobe hemiagenesis = unilateral failure of formation; left lobe more commonly absent mutations in receptor for TSH likely involved
69
What is DiGeorge Syndrome?
agenesis of thymus and parathyroid glands shortened philtrum of upper lip, low-set and notched ears nasal clefts, thyroid hypoplasia cardiac abnormalities (NCC migration issues)

NS-1 (50 decks)

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