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Head and neck > 6 - Embryology > Flashcards

6 - Embryology Flashcards

1
Q

What are the pharyngeal arches?

A

5 Mesenchymal proliferations (1-6 as 5 doesn’t form) with internal surfaces covered in endoderm, in the lateral wall of the embryonic pharynx

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2
Q

What happens to the pharyngeal grooves?

A

Clefts get obliterated, except for the 1st between 1st and 2nd arches, which becomes external auditory meatus

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3
Q

What are the pharyngeal grooves and what do they develop into?

A

Grooves on the internal surface (facing gut tube) covered in endoderm
Develop into parathyroid, thymus and tonsils

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4
Q

What is a cartilage bar and what do they develop into?

A

Cartilage associated with a pharyngeal arch
1st becomes Meckel’s cartilage, developing into mandible, malleus and incus bones
4th and 6th develop into thyroid, arytenoids and cricoids

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5
Q

Which structures are associated with the 1st pharyngeal artery?

A 
Common, internal and external carotid arteries 
Trigeminal nerve (V) 
Mandible (via intramembranous ossification from Meckel's cartilage)
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6
Q

What are the stages of intramembranous ossification?

A

Small cluster of mesenchymal stem cells for a nidus (tight cluster of cells)
Stem cells become osteoprogenitor cells, which become osteoblasts
Osteoblasts lay down osteoid - extracellular matrix containing type 1 collagen
Osteoid mineralises to form bone spicules, containing osteocytes
Spicules join to form trabeculae, which form woven bone, then mature bone

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7
Q

What are the stages of endochondral ossification?

A

Hyaline cartilage model
Primary ossification centre - perichondrium becomes periosteum, which contains osteoprogenitor cells that turn into osteoblasts
Osteoblasts secrete osteoid against shaft of cartilage - appositional growth
Chondrocytes in POC hypertrophy and secrete enzymes that calcify the matrix

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8
Q

Where are the muscles of mastication derived from?

A

1st pharyngeal arch

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9
Q

Where are the muscles of facial expression derived from?

A

2nd pharyngeal arch

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10
Q

Where is the stylopharyngeus derived from?

A

3rd pharyngeal arch

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11
Q

What are the derivatives of the 4th pharyngeal arch?

A

Cricothyroid
Levator palatini
Constrictors of the pharynx

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12
Q

Where are the intrinsic muscles of the larynx derived from?

A

6th pharyngeal arch

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13
Q

What is Reichert’s cartilage?

A

Cartilage bar that develops from the 2nd pharyngeal arch, will later form stapes and upper hyoid

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14
Q

Where is the hyoid bone derived from?

A

Upper from 2nd pharyngeal arch - Reichert’s cartilage

Lower from 3rd pharyngeal arch

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15
Q

Where is the larynx derived from?

A

4th and 6th pharyngeal arches

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16
Q

Which cranial nerve is associated with the 1st pharyngeal arch?

A

Trigeminal (V)

17
Q

Which cranial nerve is associated with the 2nd pharyngeal arch?

A

Facial nerve (VII)

18
Q

Which cranial nerve is associated with the 3rd pharyngeal arch?

A

Glossopharyngeal (IX)

19
Q

Which cranial nerve is associated with the 4th and 6th pharyngeal arches?

A

Vagus (X)

20
Q

Describe the fate of the aortic arches?

A

1st and 2nd disappear
3rd - internal carotid
4th - arch of aorta and brachiocephalic
6th - pulmonary arch

21
Q

Where is the tympanic cavity derived from?

A

1st pharyngeal pouch

22
Q

Describe the fate of the pharyngeal clefts

A

1st cleft becomes external acoustic meatus

2nd arch grows downwards, obliterating all other clefts

23
Q

Describe the consequences of abnormal pharyngeal cleft development

A

Failure to obliterate clefts 2-6
Branchial cyst can cause tissue to accumulate in the neck
Branchial fistula can cause fluid to secrete into neck

24
Q

What drives the development of the face?

A

Expansion of the cranial neural tube

25
Q

What components make up the embryological face?

A

Stomatodenum
Frontonasal prominence
1st pharyngeal arch - maxillary and mandibular prominences

26
Q

Which facial features develop from the frontonasal prominence?

A

Forehead
Bridge of nose
Nose
Philtrum (dent above cupids bow)

27
Q

Which facial features develop from the maxillary prominence?

A

Cheeks
Upper lip
Upper jaw

28
Q

Which facial features develop from the mandibular prominence?

A

Lower lip

Lower jaw

29
Q

How does the nose develop?

A

Thickening of ectoderm forms nasal placodes on FNP
Sink to become nasal pits, forming medial and lateral prominences either side
Maxillary prominences grow medially, pushing nasal prominences towards midline
Maxillary and nasal prominences fuse
Medial nasal prominences fuse in midline

30
Q

How are the nasal and oral cavities separated?

A

Maxillary prominence gives rise to 2 palatal shelves, which grow downwards into oral cavity, allowing tongue to drop
Palatal shelves grow inwards towards each other, fusing in the midline
Nasal septum grows downwards and fuses with palatal shelves

31
Q

What is a lateral cleft lip?

A

Failure of fusion of medial nasal and maxillary prominences

32
Q

What is a cleft lip and palate?

A

Failure of fusion of medial nasal and maxillary prominences

Combined with failure of palatal shelves to meet in midline

33
Q

Describe how the ears develop

A

External auditory meatus develops from 1st pharyngeal cleft
Middle ear cavity from 1st pharyngeal pouch
Ossicles from cartilage of 1st and 2nd pharyngeal arches
Auricles develop from 1st and 2nd pharyngeal arches
(Tympanic cavity from 1st pharyngeal pouch)

34
Q

How do the ears reach their final position?

A

Ears develop in the neck

As mandible grows, ears ascend to the side of the head

35
Q

Why is alcohol during pregnancy associated with mental delay?

A

Neural crest cell migration very sensitive to alcohol

36
Q

What are the typical facial features associated with fetal alcohol syndrome?

A 
Small head
Flat midface
Smooth philtrum
Thin upper lip
Underdeveloped jaw

Head and neck (14 decks)

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