1. Development of pharyngeal arches Flashcards
The pharyngeal arches first appear as tissue bulges that are separated by ____
clefts (as the cranial neuropore closes)
Other name for pharyngeal arches?
Brachial/gill arches
Pharyngeal arches are made up of which embryo layers?
Mesoderm core (source: mesoderm and neural crest) Endoderm (as an internal endoderm pouch) Ectoderm (as external cleft)
With further development each arch gives rise to
dis1nct sets of structures in _______ ___ ________
With further development each arch gives rise to
dis1nct sets of structures in head and neck
What is the stomodeum?
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.
Which 3 prominences are found at the 1st pharyngeal arch?
Frontonasal prominence
Maxillary prominence: Upper and smaller
Mandibular prominence: Lower and larger
Note: the stomodeum is closed by the oropharyngeal membrane at 24 days.
What does the mesenchyme core within the pharyngeal arches form?
Muscle (branchial muscles)
Cartilage element
Artery
Cranial nerve
Difference between pharyngeal cleft and pouch?
Pharyngeal clefts are external + ectoderm
Pharyngeal pouchs are Internal + endoderm
Origins of the pharyngeal arch core?
Paraxial mesoderm
Neural crest
What are somitomeres?
Ill defined “segments” of paraxial mesoderm in the head region rostral to somites
Paraxial mesoderm migrates into pharyngeal arches and elsewhere to form….
mostly muscle tissue of the head ( plus some connective tissue and bone)
What are ectodermal placodes?
Thickening of ectoderm that help give rise to sensory neurone/ganglia (V, VII, IX and X)
How does the neural crest give rise to pharyngeal arch?
From ventral flow around the placodes.
Gives rise to: Mesenchyme (bone, cartilage, ligaments) ganglia and nerves.
Which pharyngeal arch gives rise to the muscles of mastication (+ extra)?
Arch 1: Temporalis, masseter, mylohyoid, anterior belly of diagastric, tensor tympani, tensor veli palati
Which pharyngeal arch gives rise to the muscles of facial expression (+ extra)?
Arch 2: Facial expression (Frontalis, orbicularis oculi, orbicularis oris, buccinator) Posterior belly of digastric Stylohyoid Stapedius
Which pharyngeal arch gives rise to the muscle stylopharngeus?
Arch 3
Which pharyngeal arch gives rise to the muscles of.. -Constrictors -The soft palate -Lev v palatini -Cricothyroid -Layrnx musculature (+somites)?
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
Which cranial nerve arises from the pharyngeal arches?
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
Which pharyngeal arch gives rise to the maxillary artery?
Arch 1
Which pharyngeal arch gives rise to the corticotympanic artery?
Note: Embryonic term is “stapedial artery”
Arch 2
Which pharyngeal arch gives rise to the common and internal carotid arteries?
Arch 3
Which pharyngeal arch gives rise to part of aortic arch and part of right subclavian artery?
Arch 4
LHS arch –> Part of aortic arch
RHS arch –> Part of RHS subclavian artery
Which pharyngeal arch gives rise to the part of left pulmonary artery and part of right pulmonary artery?
Arch 6
LHS arch –> part of left pulmonary artery
RHS arch –> part of right pulmonary artery
Name the skeletal structures and ligaments produced from the 1st pharyngeal arch?
Skeletal structures (from neural crest cells):
- Mandible
- Maxilla
- Malleus
- Incus
- Zygomatic
Ligaments:
- Ant lig of malleus
- Sphenomandibular ligament
Name the skeletal structures and ligaments produced from the 2nd pharyngeal arch?
Skeletal structures (from neural crest cells):
- Stapes
- Styloid process
- Lesser horn of hyoid
- Upper body of hyoid
Ligaments:
-Stylohyoid ligament
Name the skeletal structures produced from the 3rd pharyngeal arch?
Skeletal structures (from neural crest cells):
- Greater horn of hyoid
- Lower body of hyoid
Name the skeletal structures produced from the 4th and 6th pharyngeal arch?
Hint: Larynx
Skeletal structures (from neural crest cells):
- Thyroid
- Cricoid
- Arytenoid
- Corniculate and cuneiform cartilages
- Epiglottis
- Laryngeal cartilages
During pharyngeal arch development, cartilage can form which 3 things?
Can ossify to become bone
Can form a ligament
Can disappear and is replaced by a membrane bone
Which skeletal structures of the head, face and neck are formed from mesenchyme of the origin of…
- Neural crest?
- Lateral plate mesoderm?
- Paraxial mesoderm?
- Neural crest?
- Frontal
- Sphenoid
- Squamous Temporal
- Nasal
- Lacrimal
- Zygomatic
- Maxilla
- Incisive
- Mandible
- Hyoids - Lateral plate mesoderm?
- Laryngeals - Paraxial mesoderm?
- Parietal
- Petrous temporal
- Occipitals
Describe/name the 4 pharyngeal pouches that form as a result of invagination of endoderm in the lateral walls of the pharynx?
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)
Anterior to the laryngeal orifice is the floor, what will this form?
The tongue
What is derived from the pharyngeal clefts? and how?
(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
Which is the commonest congenital disease of the neck?
Pharnygeal/brachial cleft anomalies e.g.
-Cysts (adults) and fistulas/sinuses (children)
Postion: Anterior to sternocleidomastoid
Diagnostic challenge: Presume cancerous until proven otherwise
What is meant by “rhombomere”?
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.
Role of molecular determination in neural crest migration?
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.
Neural crest cells form skeletal elements of the arches under control of pouch endoderm signals, how?
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
1/3 of birth defects are….
craniofacial defects
“3-5% of live births have craniofacial defects”
What is treacher collins syndrome?
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
What is Di George syndrome?
(Other names: 22q11 dele1on syndrome, congenital thymic hypoplasia, or third and fourth pharyngeal pouch syndrome, CATCH-22 disorder)
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.
Role of sonic hedgehog?
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
Name two examples of craniosynostosis syndromes?
where the head is abnormally shaped
Apert and crouson
Genetic causes for craniosynostosis syndromes
Mutations in FGFRs
TWIST transcription factor
EPHRIN-B1
How mutations of FGFR cause craniosynostosis?
- 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
Cartilaginous elements of arches _____ from neural crest mesenchyme
BUT
Cartilaginous elements of the _______ (arches __ +__) is from lateral plate mesoderm
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
