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(OMS1) Neuro Exam 1 > Pharyngeal Arch embryology > Flashcards

Pharyngeal Arch embryology Flashcards

1
Q

What is the pharyngeal apparatus?

A

Consists of the pharyngeal arches, pouches, grooves and membranes
Contribute to the formation of nasal cavities, mouth, larynx, pharynx and neck

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2
Q

What week do pharyngeal arches develop?

Which germ layer does this come from?

A

4th week

Neural crests, migrating into the future head and neck

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3
Q

Sequence of development of the arches

A

The 1st pair, the primordial jaws appear lateral to the developing pharynx = is the future head and neck
Arches 2-4 then appear on each side
Arches 5-6 are rudimentary and not visible on embryological surface, Arch 5 disintegrates

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4
Q

Core of each arch is made of….
External lining of each arch is made of….
Internal lining of each arch is made of …

A

Mesoderm and mesenchyme
Ectoderm
Endoderm

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5
Q

The core mesenchyme is derived from

A

Migratory neural crest cells and mesoderm cells from the prechordal plate and the paraxial mesoderm respectively

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6
Q

Pharyngeal arches function and gives rise to ….

A

Support the lateral walls of the primordial pharynx and give rise to prominences of tissue (e.g., laryngeal prominence)

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7
Q

NCC derived mesenchyme forms

A

All connective tissue in the head, including the dermis and smooth muscle (vasculature)

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8
Q

Paraxial mesoderm forms

A

Pharyngeal arch musculature

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9
Q

Lateral plate mesoderm forms

A

Angioblasts that differentiate into endothelium

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10
Q

Prechordal plate mesoderm forms

A

Extraocular musculature (Eye muscles)

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11
Q

Structures contained in the pharyngeal arches

A

Cartilagenous rod, muscular component, cranial nerve, arch artery

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12
Q

Cartilagenous rod forms …

Muscular component forms ….

A

Skeletal elements

Head and neck muscles

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13
Q

Arch artery arises from …

Course

A

Truncus arteriosus

Passes around the primordial pharynx to enter the dorsal aorta

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14
Q

PA1 cartilage is called

A

Meckel’s cartilage

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15
Q

Dorsal portion of the meckel’s cartilage forms ….
Ventral portion of the meckel’s cartilage forms ….
Perichondrium of the meckel’s cartilage forms ….

A

Malleus and Incus
Primordium of the mandible
Anterior ligament of malleus and the sphenomandibular ligament

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16
Q

What eventually happens to Meckel’s and Riechert cartilage?

A

Disintegrates and replaced by bone

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17
Q

PA2 cartilage is called

A

Riechert’s cartilage

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18
Q

Part of the dorsal region of riechert’s cartilage forms ….
Ventral region …
Perichondrium …

A
  • stapes and styloid process of temporal bone, while the rest will disintegrate
  • ossifies and forms the lesser cornu/horn of the hyoid
  • becomes the stylohyoid ligament
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19
Q

PA3 (Third arch cartilage) will…

A

Ossify and forms the greater cornu of the hyoid

20
Q

Hypopharyngeal eminence (floor of the embryonic pharynx - coming from PA3 and PA4) will form…

A

Body of the hyoid bone

21
Q

4th and 6th cartilage will form

A

4th: laryngeal cartilage, including the epiglottis (NCC derived)
6th arch: laryngeal cartilage of unk origin

22
Q

First arch muscular components forms which muscles?
Second arch muscular components forms which muscles?
Third arch?
Fourth arch?
Sixth arch?

A
  • Muscles of mastication (CN V, chewing)
  • stapedius and muscles of facial expression (CN VII)
  • stylopharyngeus (elevate and dilate, innervated by CN IX)
  • cricothyroid, levator veli palatini and constrictors of pharynx (pushes food down, CN X)
  • intrinsic laryngeal muscles (CN X, make sound)
23
Q 
Which PA is each nerve associated with? 
CN V
CN VII
CN IX
CN X
A
  • PA1 (basically sensory n. of head and neck)
  • PA2
  • PA3
  • PA4-6 (4th arch specifically supplied by the superior laryngeal branch and recurrent laryngeal branch)
24
Q

Which branch of CN V is not associated with PA1?

A

V1 (ophthalmic)

25
Q

What are the aortic arch arteries?

A

Basket like structure of arteries. initially five pairs arising from the aortic sac of the dorsal aorta)
Remodeled in development to form the great arteries of head and neck

26
Q

What are pharyngeal grooves?

A

Located between the pharyngeal arches and are lined by ectoderm

27
Q

First groove will form ….

How about grooves 2-4?

A

External acoustic meatus

Fuse together to form the cervical sinus, which disintegrate during development

28
Q

Which groove is most commonly affected in birth defects?

A

2nd groove. Cervical sinus forms caudal to this

29
Q

Cervical cysts:
Cause
Clinical

A

Remnants of cervical sinus and/or 2nd groove, collect cell debris and form cysts in the neck,
Usually painless. Cysts form inferior to angle of mandible

30
Q

Cervical sinus:
Cause
Clinical

A

2nd PA groove and cervical sinus (a hole thing that disintegrates during development) did not close and obliterate completely so you have an opening
Detected due to mucosal discharge. Commonly associated with auricular sinuses

31
Q

Cervical fistula:
Cause
Clinical

A

2nd groove and pouch persistence

Abnormal canal that opens into the tonsillar sinus on the side of the neck

32
Q

1st pharyngeal membrane forms…

A

Tympanic membrane

33
Q

1st pouch forms

A

Contacts the 1st groove which also contributes to the tympanic membrane
Tympanic cavity and mastoid antrum from the tubotympanic recess
Elongates to form the pharyngotympanic tube

34
Q

2nd pouch forms

A

Tonsillar sinus
Endoderm forms the tonsillar epithelium
Mesenchyme forms the lymphoid nodules of the palatine tonsil

35
Q

3rd pouch forms…
Dorsal portion:
Ventral portion:

A
  • inferior parathyroid
  • thymus

(these caudally migrate to accommodate brain and heart development and end up below the derivatives of the 4th pouch)

36
Q

4th pouch forms

Dorsal portion:

A

Superior Parathyroid glands (4 doesn’t move down, so it ends up superior)
Ultimobranchial body fuses with thyroid gland to give rise to parafollicular cells

37
Q

Describe the development of the thymus:

A

PA3 endoderm > thymic primordium. 3 epithelial cords

38
Q

Functions of the epithelial cords:

A

Grow into surrounding mesenchyme
Arrange around a central point and form the thymic corpuscles
Form an epithelial reticulum to house lymphocytes

39
Q

Thymus and aging

A

Active in childhood but involutes and mostly becomes adipose in adulthood

40
Q

Development of the thyroid:

A

Develops 24 days post fertilization from the floor of the developing pharynx > thyroid primordium > invaginates downward and passes ventrally to the hyoid and laryngeal cartilage
Connected to the tongue via the thyroglossal duct, which will later disintegrate

41
Q

First pharyngeal arch syndrome:
Cause
Clinical

A

Caused by insufficient migration of NCC into 1st arch during the 1st week
Malformation of eyes, ears, mandible and palate = first arch syndrome

42
Q

Treacher Collins syndrome (mandibulofacial dysostosis)
Cause
Clinical

A

Autosomal dominant, caused by mutations in TCOF1 gene. Encodes TREACLE involved in ribosome biogenesis. This protein is truncated in TCS causing apoptosis of the neural crest cells > abnormal migration

43
Q

Pierre Robin sequence:

A

Hypoplasia of mandible, cleft palate and defects of eyes and ears
Initiating defect is small mandible (micrognathia) which results in posterior displacement of tongue and obstruction of palate closure. Results bilateral cleft palate

44
Q

Agenesis of the thyroid gland:

A

Absence of thyroid gland or one of its lobes. Rare

45
Q

Thyroid hemiagenesis

A

Unilateral failure formation, left lobe commonly absent. Possibly caused by mutations in TSH receptor

46
Q

DiGeorge Syndrome:

A

No signaling of PA endoderm to NCC to migrate. Thymus and parathyroid glands do not develop. No T cells.
Clinical: congenital hypoparathyroidism, shortened philtrum of upper lip, low set and notched ears, nasal clefts and thyroid hypoplasia. Also cardiac abnormalities due to defects in aortic arch and heart

(OMS1) Neuro Exam 1 (18 decks)

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