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MD4001 Week 3 > 1. Development of pharyngeal arches > Flashcards

1. Development of pharyngeal arches Flashcards

1
Q

The pharyngeal arches first appear as tissue bulges that are separated by ____

A

clefts (as the cranial neuropore closes)

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2
Q

Other name for pharyngeal arches?

A

Brachial/gill arches

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3
Q

Pharyngeal arches are made up of which embryo layers?

A 
Mesoderm core (source: mesoderm and neural crest)
Endoderm (as an internal endoderm pouch)
Ectoderm (as external cleft)
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4
Q

With further development each arch gives rise to

dis1nct sets of structures in _______ ___ ________

A

With further development each arch gives rise to

dis1nct sets of structures in head and neck

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5
Q

What is the stomodeum?

A

The stomodeum, also called stomatodeum or stomatodaeum, is a depression between the brain and the pericardium in an embryo
Is the precursor of the mouth and the anterior lobe of the pituitary gland.

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6
Q

Which 3 prominences are found at the 1st pharyngeal arch?

A

Frontonasal prominence
Maxillary prominence: Upper and smaller
Mandibular prominence: Lower and larger

Note: the stomodeum is closed by the oropharyngeal membrane at 24 days.

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7
Q

What does the mesenchyme core within the pharyngeal arches form?

A

Muscle (branchial muscles)
Cartilage element
Artery
Cranial nerve

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8
Q

Difference between pharyngeal cleft and pouch?

A

Pharyngeal clefts are external + ectoderm

Pharyngeal pouchs are Internal + endoderm

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9
Q

Origins of the pharyngeal arch core?

A

Paraxial mesoderm

Neural crest

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10
Q

What are somitomeres?

A

Ill defined “segments” of paraxial mesoderm in the head region rostral to somites

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11
Q

Paraxial mesoderm migrates into pharyngeal arches and elsewhere to form….

A

mostly muscle tissue of the head ( plus some connective tissue and bone)

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12
Q

What are ectodermal placodes?

A

Thickening of ectoderm that help give rise to sensory neurone/ganglia (V, VII, IX and X)

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13
Q

How does the neural crest give rise to pharyngeal arch?

A

From ventral flow around the placodes.

Gives rise to: Mesenchyme (bone, cartilage, ligaments) ganglia and nerves.

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14
Q

Which pharyngeal arch gives rise to the muscles of mastication (+ extra)?

A

Arch 1: Temporalis, masseter, mylohyoid, anterior belly of diagastric, tensor tympani, tensor veli palati

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15
Q

Which pharyngeal arch gives rise to the muscles of facial expression (+ extra)?

A 
Arch 2: 
Facial expression (Frontalis, orbicularis oculi, orbicularis oris, buccinator)
Posterior belly of digastric
Stylohyoid
Stapedius
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16
Q

Which pharyngeal arch gives rise to the muscle stylopharngeus?

A

Arch 3

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17
Q 
Which pharyngeal arch gives rise to the muscles of..
-Constrictors
-The soft palate
-Lev v palatini
-Cricothyroid
-Layrnx musculature
(+somites)?
A

Arches 4-6
I.e. all muscles of pharynx apart from sytlopharyngeus (which is formed from 3rd arch) + all muscles of palate (apart from tensor veli palatini)

4th arch –> pharynx and palate muscles
6th arch–> larynx muscles

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18
Q

Which cranial nerve arises from the pharyngeal arches?

A

Arch 1 = Trigeminal nerve
Arch 2= Facial nerve
Arch 3 = Glossopharyngeal nerve
Arch 4 = Superior laryngeal branch of Vagus nerve
Arch 6= Recurrent laryngeal branch of Vagus nerve

19
Q

Which pharyngeal arch gives rise to the maxillary artery?

A

Arch 1

20
Q

Which pharyngeal arch gives rise to the corticotympanic artery?

Note: Embryonic term is “stapedial artery”

A

Arch 2

21
Q

Which pharyngeal arch gives rise to the common and internal carotid arteries?

A

Arch 3

22
Q

Which pharyngeal arch gives rise to part of aortic arch and part of right subclavian artery?

A

Arch 4
LHS arch –> Part of aortic arch
RHS arch –> Part of RHS subclavian artery

23
Q

Which pharyngeal arch gives rise to the part of left pulmonary artery and part of right pulmonary artery?

A

Arch 6
LHS arch –> part of left pulmonary artery
RHS arch –> part of right pulmonary artery

24
Q

Name the skeletal structures and ligaments produced from the 1st pharyngeal arch?

A

Skeletal structures (from neural crest cells):

  • Mandible
  • Maxilla
  • Malleus
  • Incus
  • Zygomatic

Ligaments:

  • Ant lig of malleus
  • Sphenomandibular ligament
25
Q

Name the skeletal structures and ligaments produced from the 2nd pharyngeal arch?

A

Skeletal structures (from neural crest cells):

  • Stapes
  • Styloid process
  • Lesser horn of hyoid
  • Upper body of hyoid

Ligaments:
-Stylohyoid ligament

26
Q

Name the skeletal structures produced from the 3rd pharyngeal arch?

A

Skeletal structures (from neural crest cells):

  • Greater horn of hyoid
  • Lower body of hyoid
27
Q

Name the skeletal structures produced from the 4th and 6th pharyngeal arch?

Hint: Larynx

A

Skeletal structures (from neural crest cells):

  • Thyroid
  • Cricoid
  • Arytenoid
  • Corniculate and cuneiform cartilages
  • Epiglottis
  • Laryngeal cartilages
28
Q

During pharyngeal arch development, cartilage can form which 3 things?

A

Can ossify to become bone
Can form a ligament
Can disappear and is replaced by a membrane bone

29
Q

Which skeletal structures of the head, face and neck are formed from mesenchyme of the origin of…

  1. Neural crest?
  2. Lateral plate mesoderm?
  3. Paraxial mesoderm?
A
  1. Neural crest?
    - Frontal
    - Sphenoid
    - Squamous Temporal
    - Nasal
    - Lacrimal
    - Zygomatic
    - Maxilla
    - Incisive
    - Mandible
    - Hyoids
  2. Lateral plate mesoderm?
    - Laryngeals
  3. Paraxial mesoderm?
    - Parietal
    - Petrous temporal
    - Occipitals
30
Q

Describe/name the 4 pharyngeal pouches that form as a result of invagination of endoderm in the lateral walls of the pharynx?

A

1 - Primitive tympanic cavity 2 - Palatine tonsil/tonsillar fissure
3 - Parathyroid (inferior) and thymus (migrates)
4 - Parathyroid gland (superior) and Ultimobranchial body (parafollicular (C) cells of thyroid)

31
Q

Anterior to the laryngeal orifice is the floor, what will this form?

A

The tongue

32
Q

What is derived from the pharyngeal clefts? and how?

A

(Cleft = external)
1st cleft:
Dorsal part of the 1st cleft –> the external auditory meatus + external part of the tympanic membrane. Deepest part –> Tympanic membrane (ear drum)

2nd cleft:
Proliferates and overgrows the 3rd and 4th arches

2nd, 3rd and 4th cleft:
Lose contact with the exterior forming cervical sinus. Soon disappears once connection lost

33
Q

Which is the commonest congenital disease of the neck?

A

Pharnygeal/brachial cleft anomalies e.g.
-Cysts (adults) and fistulas/sinuses (children)
Postion: Anterior to sternocleidomastoid
Diagnostic challenge: Presume cancerous until proven otherwise

34
Q

What is meant by “rhombomere”?

A

In the vertebrate embryo, a rhombomere is a transiently divided segment of the developing neural tube, within the hindbrain region (a neuromere) in the area that will eventually become the rhombencephalon.

35
Q

Role of molecular determination in neural crest migration?

A

HOX genes are key controllers of rostrocaudal patterning in the head

3 streams of neural crest cells migrate mostly from rhombomeres (segments of hindbrain). The neural crest cells express homeodomain-containing transcription factor OTX and HOX genes, to the pharyngeal arches.
These provide guidance cues for sensory cranial nerves growing back from ganglia.

36
Q

Neural crest cells form skeletal elements of the arches under control of pouch endoderm signals, how?

A

Neural crest cells migrate from rhombomere into arch carrying (OTX/HOX) codes
• Neural crest cells respond to local patterns of ENDODERM signals (FGF, BMP, PAX, SHH)
–> Specifies mesenchymal expression pattern and arch characteristics

37
Q

1/3 of birth defects are….

A

craniofacial defects

“3-5% of live births have craniofacial defects”

38
Q

What is treacher collins syndrome?

A

First/second arch syndrome
MoA:
• Defective protein called Treacle (TCOF1 gene)
• Failure of formation/ apoptosis of neural crest cells and migration into first and second pharyngeal arches

Symptoms:
•   Abnormal eye shape  
•  Micrognathia (small jaw)
•  Conductive hearing loss,
•  Underdeveloped zygoma
•  Malformed ears
39
Q

What is Di George syndrome?
(Other names: 22q11 dele1on syndrome, congenital thymic hypoplasia, or third and fourth pharyngeal pouch syndrome, CATCH-22 disorder)

A

Cause: 3rd and 4th pouches fail to develop and thymus and parathyroids are defective

Symptoms:
•  Cardiac abnormality (especially tetralogy of Fallot)   
•  Abnormal facies* 
•  Thymic aplasia 
•  Cleft palate 
•  Hypocalcaemia
  • More frequent cle7 lip and palate, small jaw, small upper lip, eyes slanted upward/downward, lowTset abnormal folding ears.
40
Q

Role of sonic hedgehog?

A

SHH is involved in craniofacial patterning, it governs the width of facial features
Low levels –> Narrowing and fusion e.g. cylopia
High levels–> Widening structures duplicated. e.g. diprosopus

41
Q

Name two examples of craniosynostosis syndromes?

where the head is abnormally shaped

A

Apert and crouson

42
Q

Genetic causes for craniosynostosis syndromes

A

Mutations in FGFRs
TWIST transcription factor
EPHRIN-B1

43
Q

How mutations of FGFR cause craniosynostosis?

A
  • Mutations cause a gain of function –> cons1tu1ve ac1va1on of receptors
  • FGF signalling activates bone calcification and reduces cell proliferation in the mesenchyme at the suture – generating premature fusions
  • Premature fusion (amongst other affects such as syndactaly) results
  • Mutations spontaneous in the paternal line increase with age
44
Q

Cartilaginous elements of arches _____ from neural crest mesenchyme

BUT

Cartilaginous elements of the _______ (arches __ +__) is from lateral plate mesoderm

A

Cartilaginous elements of arches 1,2,3 from neural crest mesenchyme

BUT

Cartilaginous elements of the laryngeals (arches 4 +6) is from lateral plate mesoderm

MD4001 Week 3 (12 decks)

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