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Oral biology > Pharyngeal Arch Development > Flashcards

Pharyngeal Arch Development Flashcards

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1
Q

What makes up the pharyngeal apparatus?

A

1) pharyngeal arches: 1-4, 6
2) pharyngeal grooves: 4 pairs
3) pharyngeal pouches: 4 or 5 pairs
4) pharyngeal membrane: between arches

  • arches emerge at neural tube closure
    • approx. 4 weeks
    • contain all 3 layers
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2
Q

What are the layers located on the arch?

A
  • ectoderm is on the outside
  • endoderm is on the inside
  • neural crest is between the ectoderm and endoderm
  • mesoderm surrounds an artery, which is surrounded by the neural crest
  • clefts are on the outside
  • pouches are on the inside
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3
Q

What happens to the oropharyngeal membrane?

A

breaks down during week 4, connects stomodeum to primitive gut

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4
Q

What are the components of the pharyngeal arches?

A
  • aortic arch
  • carilaginous rod
  • muscular component
  • nerve
  • during the 3rd week the primary tissue is mesenchyme, but as the embryo reaches the 4th week it becomes neural crest
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5
Q

What is derived from pharyngeal arch 1?

A
  • Bone: mocker’s cartilage, maxilla, mandible, malleus, incus
  • Muscles: muscles of mastication
  • nerve: Trigeminal
  • Arteries: Maxillary and Ext. carotid
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6
Q

What is derived from pharyngeal arch 2?

A
  • Bone: Stapes, styloid process, less horn and upper portion of the body of hyoid
  • Muscles: muscles of facial expression
  • Nerve: facial nerve
  • Arteries: stapedial
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7
Q

What is derived from pharyngeal arch 3?

A
  • Bone: Greater horn and lower portion of body of the hyoid
  • Muscles: Stylopharyngeus
  • Nerve: Glossopharyngeal
  • Arteries: Common and Int. carotid
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8
Q

What is derived from the 4th arch?

A
  • Bone: Laryngeal cartilages
  • Muscles: Constrictors of pharynx
  • Nerve: Vagus and Sup. laryngeal
  • Arteries: Aortic and subclavian
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9
Q

What is derived from the 6th arch?

A
  • Muscles: intrinsic m. of larynx
  • Nerve: Recurrent laryngeal
  • Arteries: Pulmonary
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10
Q

How is the first arch structured and formed?

A
  • mandibular process –> lower lip , lower face, lower cheek regions, chin, mandible, body of the tongue
  • Maxillary process –> mid face, upper cheek regions, upper lip sides, Secondary palate, maxilla, zygomatic bones, secondary palate
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11
Q

What are some pharyngeal anomalies?

A
  • First arch syndrome is congenital
    • failure of neural crest to properly migrate into the first arch

1) Treacher-Collins: hypoplasia of arch derived facial bones; down-slanting of palpebral fissures, lower eyelid colhbomas, ear deformations, cleft palate and tooth defects
2) Pierre Robin: hypoplasia of the mandible (micrognathia), misplacement of tongue (glossoptosis) cleft palate, defects of the eye and ear, airway obstruction

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12
Q

What becomes of the grooves/clefts?

A
  • Lined with ECTODERM
  • Cleft one is usually the only one not obliterated
  • clefts 2-4 persist during abnormalities
  • Pharyngeal cleft 1: becomes external auditory meatus
  • Abnormality
    • Congenital auricular sinuses and cysts: small sinuses and cysts commonly found in a triangular area of skin ant. to the ear; may be recent of pharyngeal groove –> first or second arch defect
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13
Q

What is a lateral cervical sinus abnormality?

A

uncommon, open externally, failure of second groove or cervical sinus to obliterate

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14
Q

What is a internal branchial groove defect?

A

Rare, persistant, 2nd pouch, open into intratonsillar cleft (into pharynx)

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15
Q

What are the pharyngeal pouches?

A
  • form as pits internally in the pharynx, between the arches
  • pouch linings are endodermal
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16
Q

What does the first pharyngeal pouch give rise to?

A
  • Middle Ear
  • Distal: together with lining of 1st cleft, form tympanic membrane
    • widens and forms tympanic cavity
  • Proximal: stays narrow, forms auditory tube
17
Q

What happens during middle ear development?

A
  • Ossicles: 1st and 2nd arch cartilages, from neural crest
  • tympanic membrane: 1st cleft/pouch, from neural crest
  • tympanic cavity and internal auditory meatus: 1st pouch
18
Q

What does the second pharyngeal pouch give rise to?

A
  • Lining of the crypt in the palatine tonsils
  • Tonsils by themselves are mostly composed of mesoderm
  • pouch forms the crypts lining, which is epithelium and continuous with lining of mouth
19
Q

What does the third pharyngeal pouch give rise to?

A
  • Inferior parathyroid gland and the thymus
  • Dorsal wing: inferior parathyroid glands
  • Ventral wing: thymus
  • Inf. parathyroid gland travels with the thymus before moving over to the thyroid
20
Q

What does the fourth pharyngeal pouch give rise to?

A
  • Superior parathyroid gland and the ultimobranchial body
  • Dorsal wing: sup. parathyroid glands
  • Ventral wing: ultimobranchial body –> embryonic structure, contains C-cells
21
Q

What abnormalities arise from migration?

A
  • Cervical thymus: cord of thymus persists in neck on path of descent
  • Accessory Thymus: piece of thymus remaining in path of descent
22
Q

What abnormalities arise from pharyngeal pouches?

A
  • DiGeorge Syndrome: failure of 3rd and 4th pouches to differentiate into thymus, parathyroid
    • neural crest defect
  • Catch 22: Cardiac abnormality, thymus aplasia, cleft palate, hypo calcemia and thryoidism
  • Tetralogy of Fallot: pulmonary stenosis (R. ventricular hypertrophy
23
Q

What becomes of the pharyngeal membrane?

A
  • form the epithelia of the grooves and pouches as they approach each other
  • Oropharyngeal membrane: technically not a pharyngeal membrane. Marks site where ectoderm and endoderm meet. Glossopalantine arch marks location
  • Tympanic membrane: derived from layers between first cleft and 1st pouch
    • 1st ectoderm and endoderm only, then neural crest moves in
    • remaining regions between arches do not remain as membranes –> obliterate during development
24
Q

What are the importance of HOX genes during pharyngeal arch formation?

A
  • regulate A-D identity
  • Neural crest cells with different A-P ID as determined by hox expression, migrate from the rhombomeres into the pharyngeal arches
  • Loss of Hox expression causes arch 2 to lose its A-P ID, arch 2 gives rise to duplicate arch 1 structures
25
Q

What arches develop the tongue?

A
  • Arch 1: from the ant. 2/3 of epithelium
  • Arch 2: it is covered up as arch 3 grows
  • Arch 3: forms most of the remaining 1/3 of tongue epithelium
  • Arch 4: forms just a bit of tongue at the very back of the throat
26
Q

What is the timeline for tongue development?

A
  • 4 weeks: arch 1 forms meidan swelling: median tongue bud
  • 4 weeks: arch 2 forms midline swelling called copula
    • this gives rise to become the post. 1/3 of tongue
    • epiglottis arises post. to hypopharyngeal eminence
  • 5 weeks: arch 1 form lateral swellings: distal tongue buds
    • these become the ant. 2/3 of tongue
  • weeks 5-6: arch 2 is overgrown by hypo pharyngeal eminence from arches 3 and 4
27
Q

How do tongue muscles form?

A

-occipital somites give rise to these muscles, so they are not pharyngeal origin (except palatalglossus)

28
Q

What is the terminal sulcus?

A

-Dividing line between oral tongue and pharyngeal tongue (ant. 2/3 and post. 1/3), CN V and IX

29
Q

How does the thyroid gland develop?

A
  • Forms from the endodermal diverticulum, post. to the floor of the 1st arch –> NOT pharyngeal pouch
  • Not bilateral, forms at midline
  • diverticulum elongates into the thyroglossal duct - gland remains in contact with tongue early, but duct is normally obliterate later
  • site where duct connects with tongue –> foramen cecum
  • thyroid gland migrates down to sit on the ant. of the trachea
30
Q

What are some thyroid abnormalities?

A
  • failure of thryoglossal duct to completely pinch off and degenerate
  • may form anywhere along the course followed by the thyroglossal duct
  • most seen by 5 yr olds
  • asymptomatic unless infected
  • midline, painless, movable neck mass
  • sinuses are open, cysts are closed

Oral biology (6 decks)

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