Lecture 7: Pharyngeal Arches Flashcards
What are the ectodermal contributions to the pharyngeal arches?
- Groove (cleft)
- Covering
What are the Mesoderm/Neural crest contributions to the pharyngeal arches?
Mesoderm = muscle and aortic arch
Neural crest = skeletal, cartilage, and CT
What are the endodermal contributions to the pharyngeal arches?
- Pouch
- Lining
What CN is the 1st, 2nd, 3rd, 4th, and 6th pharyngeal arches associated with?
1st = CN V
2nd = CN VII
3rd = CN IX
4th and 6th = CN X
What week do the pharyngeal arches begin developing?
Week 4!
What does the ectodermal cleft of the 1st pharyngeal arch give rise to?
- External auditory meatus
- External tympanic membrane
What does the ectodermal covering of the 1st pharyngeal arch give rise to?
- Epidermis of face
- Roof of stomodeum (mouth)
- Enamel organs
- Parotid gland
- Pituitary gland (anterior)
- Part of ear (arch 1 and 2)
What does the ectodermal covering of the 2nd, 3rd, 4th, and 6th arhces give rise to?
2nd: epidermis of upper auricle and upper neck
3rd: epidermis of middle neck
4th: covering obliterates
6th: epidermis of lower neck
What is a lateral cervical (branchial) cyst caused by; where does it develop; seen by what age?
- 2nd arch usually grows down over arches 3 and 4, but sometimes space is not filled and lateral cervical sinus forms
- Remnants of part of the cervical sinus and/or 2nd pharyngeal groove
- Develop anywhere along anterior border of the SCM
- Often seen by age 5
What are the major cranial neural crest neurocistopathies?
- Aorticopulmonary septation defects of heart
- Anterior chamber defects of eye
- Cleft lip and/or cleft palate
- Frontonasal dysplasia
- DiGeorge Syndrome
- Certain dental anomalies
What structures develop from the neural crest cells of the 1st pharyngeal arch?
- Meckel’s cartilage (where mandible forms)
- Sphenomandibular ligaments
- Malleus
- Incus
What structures develop from the neural crest cells of the 2nd pharyngeal arch?
- Reichert cartilage
- Lesser cornu and upper body of hyoid bone
- Stylohyoid ligament
- Styloid proces
- Stapes
What structures develop from the neural crest cells of the 3rd pharyngeal arch?
Greater cornu and lower body of hyoid bone
What structures develop from the neural crest cells of the 4th and 6th pharyngeal arches?
Thyroid cartilage of larynx
Where do the extraocular muscles arise from embryologically; what innervates these muscles?
- Prechordal plate mesoderm
- Oculomotor (CN III)
Where do the muscles of the tongue (extrinsic/intrinsic lingual ms.) arise from embryologically; what are they innervated by?
- Occipital myotomes
- Hypoglossal (CN XII)
Which muscles arise from the mesodermal portion of the 1st pharyngeal arch; what CN innervates them?
- Muscles of Mastification
- Mylohyoid, Anterior belly of Digastric, Tensor Veli Palatini, and Tensor Tympani
- Mandibular division of Trigmeninal (CN V)
Which muscles arise from the mesodermal portion of 2nd pharyngeal arch; what CN innervates them?
- Muscles of facial expression
- Buccinator, Auricular ms., Occipitofrontalis, Posterior belly of Digastric, Stylohyoid, Stapedius, and Platysma
- Facial (CN VII)
Which muscle arises from the mesodermal portion of the 3rd pharyngeal arch; what CN innervates them?
- Stylopharyngeus
- Glossopharyngeal (CN IX)
Which muscles arise from the mesodermal portion of the 4th pharyngeal arch; what CN innervates them?
- Cricothyroid, Inferior Pharyngeal Constrictor
- Superior laryngeal branch of Vagus (CN X)
Which muscles arise from the mesodermal portion of the 6th pharyngeal arch; what CN innervates them?
- Intrinsic laryngeal muscles (except cricothyroid)
- Recurrent laryngeal branch of Vagus (CN X)
What does the 1st endodermal pouch form?
Inner ear structures:
- Auditory tube
- Middle ear cavity
What does the 2nd endodermal pouch give rise to?
- Palantine Fossa, necessary for palantine tonsils (secondary lympoid organ that provides defense against microorganisms that enter through oral cavity)
- Thyroid gland
What ‘derm layers form the palantine fossa and palantine tonsil?
- Palantine Fossa (endoderm - 2nd pouch)
- Palantine Tonsil (mesoderm)
What does the dorsal and ventral portions of the 3rd endodermal pouch give rise to?
Dorsal - inferior parathyroid glands
Ventral - thymus
What does the dorsal and ventral portions of the 4th endodermal pouch give rise to?
Dorsal - Superior parathyroid glands
Ventral - Ultimobranchial (ultimopharyngeal) body
What is the significance of the Ultimobranchial body?
Recruits neural crest cells and these cells will become calcitonin producing C cells
Which endodermal pouches descend and the significance?
- Pouches 3 and 4
- Descend w/ elongation of the fetus and pouch 3 seems to descend MORE inferiorly than pouch 4
When does the thyroid begin development and where; when is it in the adult position?
- Develops on day 24 (week 4)
- The first gland to develop!
- Begins in the oral cavity and descends through the thyroglossal duct
- Reaches its adult postion by 7th week
Thyroglossal duct cysts and sinuses are always found where?
Midline!
What abnormality is shown here?
Thyroglossal Duct Sinus (open)
What abnormality is shown here?
Thyroglossal Duct Cyst
What is the function of the thyroglossal duct and why is it clinically significant?
- During relocation, the thyroid gland is attached to the foramen cecum by the thyroglossal duct.
- This duct normally dissapears but remnants of epithelium may remain and form a thyroglossal duct cyst at any point along the path
- Most of these cysts are in the neck, anterior and just inferior to the body of the hyoid in the midline
How does an ectopic thyroid develop and what are some of the different types?
- As cells of the thyroid are migrating from base of the tongue down to the adult position some may not move appropriately and you will end up with thyroid tissue in abnormal areas
- Lingual thyroids
- Cervical thyroids
- Pyramidal lobe
What is a pyramidal lobe of the thyroid gland a remenant of?
Thyroglossal duct remenant
What are the 2 main manifestations of the First Arch Syndrome; what is the underlying embryologic issue?
1) Treacher Collins Syndrome
2) Pierre Robin Sequence
- Base of the problem is neural crest cell migration and abnormal signaling to the other germ layers
What is the inheritance pattern, defective gene, and characterization of Treacher Collins Syndrome?
- Autosomal dominant disorder
- TCOF1 gene
- Malar hypoplasia
- Down-slanting palpebral fissures
- Defects of lower eyelids
- Deformed external ears (middle and inner ear may be affected)
What is the inheritance pattern and characterization of Pierre Robin Sequence?
- Rarely it is inherited in an autosomal dominant pattern (usually is spontaneous)
- Hypoplasia of mandible
- Cleft palate
- Defects of eyes and ears
What is the dective gene in DiGeorge Syndrome?
Microdeletion of q11.2 chromosome on chromosome 22
What defects are seen in DiGeorge Syndrome; characteristics of the disease?
- No thymus and parathyroid glands (Pouches 3 and 4)
- Defects in cardiac outflow tracts
Characteristics:
- Hypoparathyroidism
- Susceptible to infection
- Anomalies of mouth, Low-set notched ears, Nasal clefts, Thyroid hyoplasia, Cardiac abnormalities
Which pouch is responsible for cellular immunity, self versus non-self, immune response to viral infected cells, graft rejections, and tumor surveillance?
3rd pouch (endoderm)
Explain the difference between the mixed nerves and their sensory branches from the pharyngeal arches?
- Mixed nerves travel into their respective arch
- Sensory branches are given off and ascend to the pharyngeal arch above for innervation
- i.e., Facial n (CN VII) travels in the 2nd pharyngeal arch sending in mixed nerves, but also gives off a sensory branch, the chorda tympani, which travels into the 1st pharyngeal arch and innervates taste buds of anterior tongue
What is the sensory branch and mixed nerves in 1st, 2nd, 3rd, 4th, and 6th pharyngeal arches?
