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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
Q

What muscles originiate from PA6?

A

Intrinisc ms of larynx *except cricothyroid*

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26
Q

What is Meckel’s cartilage?

A

cartilage of PA1

dorsal nodules –> form malleus and incus

perichondrium –> ant L of malleus and sphenomandibular L

ventral parts –> mandible

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27
Q

what is Riechert’s cartilage and what does it form?

A

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

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28
Q

How does the stylohyoid L form?

A

cartilage of PA2 (reichert’s) btw styloid and hyoid regresses –> perichondrium forms stylohyoid L

29
Q

What do the greater and lesser horns of the hyoid bone arise from?

A

Lesser = from Reichert’s cartilage of PA2

greater = from third arch cartilage

30
Q

What does the third arch cartilage form?

A

greater horn of of hyoid bone

contributes to body of hyoid bone

31
Q

What forms the body of hyoid bone?

A

hypopharyngeal eminence = prominence in floor of embryo pharynx from 3 and 4 –> body of hyoid bone

32
Q

What forms from the 4th and 6th arch cartilages?

A

fuse –> laryngeal cartilages (except epiglottis)

(5th arch, if present, is rudimentary and has no derivatives)

33
Q

What are the pharyngeal arch muscles derived from?

A

paraxial mesoderm and prechordal plate

34
Q

what types of nerves supply the dermis and mucous membranes of the head and neck?

A

special visceral afferents

35
Q

What are the arteries of the 3rd arch?

A

common and internal carotids

36
Q

What does the distal internal carotid a form from?

A

extensions of dorsal aorta

37
Q

How do the external carotid As form?

A

de nove from common carotids

38
Q

where are the 1st pair of pharyngeal pouches?

How many are there total?

A

1st pair btw 1st and second arches (internal, lined w/ endoderm)

5 pairs total

39
Q

What are the pharyngeal membranes?

A

where the pouch endoderm contacts ectoderm of pharyngeal grooves

(separates pouch from groove)

40
Q

What forms the tympanic membrane?

A

1st pharyngeal membrane + intervening mesenchyme

(endo + NC + ecto)

41
Q

What does the 1st pharyngeal pouch form?

A

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
Q

What does the 2nd pharyngeal pouch form (in general)?

A

largely obliterated as palatine tonsil forms

part of pouch –> tonsillar sinus = depression btw palatoglossal and palatopharyngeal arches

43
Q

What does the endoderm of the second pouch form?

A

proliferates –> central core breaks down –> tonsillar crypts (remainder of endo forms epithelium of tonsils and lining of crypts)

44
Q

What does the mesenchyme of the second pouch form?

A

around tonsillar crypts (endoderm) –> turns into lymphoid tissue at 20 weeks

will form lymphatic nodules of palatine tonsil

45
Q

What does the 3rd pharyngeal pouch form?

A

dorsal part = solid, bulbar –> 6th week: inferior parathyroid gland

ventral part = elongated and hollow –> proliferates and obliterates cavities –> forms thymus

46
Q

What occurs to the location of derivatives of 2nd-4th pouches?

A

glands lose connections w/ pharynx due to growth of brain and heart –> caudally displaced

47
Q

What do the parathyroid glands develop from?

A

4th pouch –> superior glands

3rd pouch –> inferior glands

48
Q

What does the 4th pharyngeal pouch form?

A

dorsal, bulbar part: epithelium –> superior parathyroid gland

elongated, ventral part

49
Q

What are pharyngeal grooves?

A

separate arches externally = ectoderm

1-4

arise duing 4th and 5th weeks

50
Q

What do the 1st pharyngeal grooves form?

A

persist as external auditory meatus

51
Q

What do pharyngeal grooves 2-4 form?

A

form cervical sinus –> obliterated 7th week

defects of 2nd groove are common

52
Q

what are cervical/branchial cysts?

A

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
Q

How does the thyroid gland develop?

A

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
Q

What occurs at 7 weeks of thyroid gland development?

A

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
Q

What is the pyramidal lobe of the thyroid?

A

lobe extending superiorly from isthmus

persists in ~50% of people

56
Q

What occurs at 10 weeks of thyroid gland development?

A

cords divided into cellular groups and a lumen

cells in single layer around follicles

57
Q

What occurs at 11 weeks of thyroid gland development?

A

colloid appears and synthesis of TH starts

58
Q

What occurs at 20 weeks of thyroid gland development?

A

levels of fetal TSH and thyroxine increase

59
Q

What occurs at 35 weeks of thyroid gland development?

A

fetal TSH adn thyroxine reach adult levels

60
Q

What is the ultimopharyngeal body?

A

elongated ventral part of 4th pouches –> fuse with thyroid gland

form parafollicular cells (NC derived) –> calcitonin

61
Q

When do the parathyroid glands form?

A

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
Q

How do the cells of the thymus develop?

A

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
Q

What is first arch syndrome?

A

abnormal dev of first arch –> malformation of eyes, ears, mandible, and palate

insufficient NCC migration during 4th week

64
Q

What is Treacher-Collins syndrome?

A

mandibulofacial dysostosis

AD inheritance: mutations in TCOF1 –> malformed TREACLE protein –> ribosomes not formed right in NCCs –> proteins not formed right –> increased apoptosis of cranial NCC

molar hypoplasia w/ down-slanting palpebral fissures, other face defects

form of 1st pharyngeal arch syndrome

65
Q

what is Pierre Robin sequence?

A

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
Q

What is micrognathia?

A

small mandible

see in Pierre Robin sequence

67
Q

Is it more common to have extra thyroid tissue or agenesis?

A

extra tissue

68
Q

What is agenesis of thyroid gland?

Hemiagenesis?

A

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
Q

What is DiGeorge Syndrome?

A

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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