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Head and Neck > Session 6 - development of the head and neck > Flashcards

Session 6 - development of the head and neck Flashcards

1
Q

how do the parathyroids, thymus, palatine tonsils and thyroid develop

A

develop from endoderm lined gut tube in the pharynx

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2
Q

what are the building blocks for the head and neck region

A

pharyngeal arches and frontonasal porminence

each arch has an associated artery, nerve and cartilage bar

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3
Q

what are the pharyngeal arches

A

prominent expansion of tissue in the embryonic
head and neck, one of a series of segments in this
region

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4
Q

what is a pharyngeal pouch

A

the internal surface of a pharyngeal arch, lined by
endoderm of the primitive gut tube
each arch has an associated pouch

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5
Q

which arches are associated with which cranial nerve

A 
1 - CNV
2- CNVII
3- CNIX
4- CNX
6-CNX
CNXI and CNXII have relationship with the pharyngeal arch system
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6
Q

how many arches are there

A

5 in total numbered 1-6

the 5th does not form in humans

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7
Q

what is derived from pharyngeal arch 1

A

muscles or mastication

meckel’s :malleus and incus plus a template for the formation of the mandible

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8
Q

what is derived from pharyngeal arch 2

A

muscles of facial expression

reichert’s: stapes plus upper part of hyoid

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9
Q

what is derived from pharyngeal arch 3

A

stylopharyngeus- The stylopharyngeus is a muscle in the head that stretches between the temporal styloid process and the pharynx. raise the pharynx and larynx during deglutition (swallowing) and laterally draws the pharyngeal walls up
remainder of hyoid bone

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10
Q

what is derived from pharyngeal arch 4

A

circothyroid
levator palatini
constrictors of the pharynx
cartilages of the larynx

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11
Q

what is derived from pharyngeal arch 6

A

intrinsic muscles of the larynx

cartilages of the larynx

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12
Q

what does the first pouch become

A

it is the largest

and becomes the tympanic cavity where the middle ear develops

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13
Q

what happens to the pharyngeal clefts

A

the first cleft becomes the external acoustic meatus

the second arch grows down to cover others, obliterating all other celfts

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14
Q

what happens if there is abnormal development of the pharyngeal clefts

A

you get branchial cysts or fistulae
occur on anterior border of SCM
allows tissue fluid to develop in neck

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15
Q

what derives the development of the face

A

expansion of the cranial neural tube
appearance of a complex tissue system associated with- the cranial gut tube and the outflow of the developing heart
development of the sense organs and the need to separate the respiratory tract from the GI tract

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16
Q

what does the face develop from

A

• Facial primordia
– 1st pharyngeal arch becomes the maxillary and mandibular prominences
– Frontonasal prominence (FNP)
Surrounds ventro-lateral part of the forebrain

• Primordia of eyes

17
Q

what does the FNP give rise to

A

forehead
bridge of nose
nose
philtrum

18
Q

what does the maxillary prominence give rise to

A

cheeks
lateral upper lip
lateral upper jaw

19
Q

what does the mandibular prominence give rise to

A

lower lip and jaw

20
Q

how does the nose develop

A 
• Nasal placodes (thickening of ectoderm) appear on
frontonasal prominence
• Then sink to become the nasal pits
• Medial and lateral nasal
prominences form on either side of the pits
• maxillary prominences grow medially,
pushing the nasal prominences closer
together in the midline
• Maxillary prominences
fuse with medial nasal prominences
• Medial nasal
prominences then fuse in
the midline
21
Q

how do the nasal and oral cavities seperate

A

• Fusion of medial nasal prominences creates the intermaxillary segment
– Labial component: philtrum
– Upper jaw: 4 incisors
– Palate: primary palate
• Main part of definitive palate is secondary palate
– Derived from palatal shelves derived from maxillary prominences

22
Q

what gives rise to the two palatal shelves

A

maxillary prominence

the two palatal shevles grow vertically downwards into the oral cavity on each side of the developing tongue

23
Q

what happens when the two palatal shelves grow

A

they grow towards each other and fuse in the midline

the nasal septum develops as a midline down-growth and ultimately fuses with the palatal shelves

24
Q

how do you get a lateral cleft lip

A

Failure of fusion of medial nasal prominence & maxillary prominence

25
Q

how do you get a cleft lip and palate

A

Failure of fusion of medial nasal prominence & maxillary prominence
Combined with failure of palatal shelves to meet in midline

26
Q

other than aesthetics what problems might occur with a cleft lip and palate

A

impaired speech development and ability to feed

27
Q

how does the ear develop

A

• External auditory meatus develops from the 1st Ph cleft
• Middle ear cavity and ossicles develop from 1st pharyngeal pouch and cartilages of 1st and 2nd arches
respectively
• Auricles develop from proliferation within the 1st and 2nd Ph Arches surrounding the meatus

28
Q

how do the ears reach their correct position

A 
• External ears develop
initially in the neck
• As mandible grows the ears
ascend to the side of the
head to lie in line with the
eyes
• All common chromosomal
abnormalities have
associated external ear
anomalies
29
Q

what are the features of fetal alcohol syndrome

A

small head, low nasal bridge, smooth philtrum, small eye openings, short nose, thin upper lip, flat midface, epicanthal folds

30
Q

why should you not even drink a small amount of alcohol during pregnacny

A
  • There is no known safe level of alcohol consumption during pregnancy
  • Facial skeleton derived from neural crest cells populating the pharyngeal arches
  • Neural crest migration as well as development of the brain are extremely sensitive to alcohol
  • Incidence of FAS & ARND = 1 / 100 births

Head and Neck (11 decks)

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