Development Of Pharyngeal Arches Flashcards
What were pharyngeal arches originally called?
-brachial arches
Where are the pharyngeal arches?
-surrounds the foregut where the structures that develop into the upper respiratory and proximal digestive systems are located
How many pharyngeal arches are there?
6
What are the three principle components of the pharyngeal arches?
- pharyngeal arch (skeletal, muscular, nerve, and artery component)
- pharyngeal clefts (external)
- pharyngeal pouches (internal)
- CAP
Pharyngeal arches are formed by what
Neural crest
How is the face developed?
- neural crest derived mesenchyme from the first and second arches migrates into the developing face
- will give rise to binge and cartilage
- muscle from mesoderm
- associated with specific nerve and arteries
What forms the facial skeleton?
-neural crest cells
What forms the posterior portions of the neurocranium and basicranium?
-mesoderm
Coronal and sagittal sutures may contain what?
-neural crest
Anterior portion of the sphenoid and frontal bones are derived from what?
-neural crest
What skeletal elements are derived from arch 1?
- neural crest -> cartilaginous rod (Meckel’s cartilage)
- malleus and incus
- Meckel’s cartilage -> mandible
- sphenomandibular ligame-maxilla, zygomatic, and part of the temporal bone in the maxillary portion of the first arch
What comes from the first arch?
- frontonasal region
- maxillary/mandibular prominences
Dorsal to the first arch is an elevation formed by the underlying ________ ________, the sensory ganglion for the nerve that supplies tissues derived from the first arch.
-trigeminal ganglion
What is required for normal development of the upper lip?
-Union of nasomedial prominence with the nasolateral prominence and maxillary prominence
Muscles of the arches are _______ derived.
Mesodermally
What muscles are derived from arch 1?
- temporalis
- massester
- mylohyoid
- ant. Belly of digastric
What muscles are derived from arch 2?
- buccinator
- orbicularis oris
- post belly digastric
- platysma
- frontalis
- orbicularis oculi
- occipitalis
What muscles are derived from arch 3?
-stylopharyngeus
What muscles are derived from arches 4 and 6?
- levator veli palatini
- pharyngeal muscles
- intrinsic muscles of larynx
What nerves are derived from arch 1?
- trigeminal nerve, V
- mandibular division V3
What nerve is derived from arch 2?
Facial nerve, VII
What nerve is derived from arch 3?
Glossopharyngeal nerve, IX
What nerve is derived from arches 4 and 6?
-vagus nerve, X
When does cheilogenesis occur?
Week 5
What does the frontonasal prominence form?
-forehead, bridge of nose, medial and lateral nasal prominences
What does the maxillary prominence from?
-cheeks, lateral portion of upper lip
What does the medial nasal prominence form?
-philtrum of upper lip, crest and tip of nose
What does the lateral nasal prominence form?
-Alae of nose
What does the mandibular prominence form?
-lower lip
When does palatogeneis take place?
5-12 weeks
When are BMPs expressed and for what?
- expressed early
- superficial location-palatial shelves
When is Shh expressed and for what reason?
- early induction of facial primordia
- medial edge epithelia-palatal shelves
- this is different -> instead of keeping layers apart, now epithelia must fuse
What does Tbx22 induce formation of?
Tongue
What induces ankyloglossia?
- mutations in T box transcription factor Tbx22
- can lead to heritable ankyloglossia with or without CL, CP
What are oro-facial clefts?
- separation or opening in a structure of the face: all skeletal elements derived from arch 1
- cleft lip and cleft palate (hard, soft)
- isolated or combined
- unilateral or bilateral
- genetic: either principal birth defect or symptom of hundreds of different syndromes
What is median cleft lip/”hare lip”?
-due to the incomplete merging of the two medial nasal prominences, therefore leading to most cases (with deep midline grooving of the nose) to various forms of bifid nose
What is a complete, unilateral cleft palate?
- a complete cleft palate involves a cleft of the palate and the alveolus
- open communication between oral and nasal cavities
- bovine grafts are required
- orthodontic treatment is required
What is a complete, bilateral cleft palate?
- leaves the premaxilla unattached, allowing it to grow forwards
- premaxilla is unattached and carries the upper four central teeth
- a double bone graft at the time the permanent teeth are erupting is required for this cleft
What are lateral facial clefts?
- macrostomia
- hypoplasia or incomplete fusion of maxillary and mandibular prominences
- large mouth (unit or bilaterally)
What are classic arch 1 abnormalities?
- Treacher-Collins syndrome
- Pierre Robin syndrome
What is Treacher-Collins syndrome?
- mandibulo-facial dysostosis
- underdevelopment of structures associated with arch 1
- downward slanting eyes, small mandible, and malformed/absent ears
- autosomal dominant
- protein appears to assist in protein sorting during development
- prenatal testing
What is Pierre Robin syndrome?
- micro/retrognathia
- glossoptosis
- airway obstruction
- treatment is surgery
What skeletal elements are derived from arch 2?
- initially bar of cartilage -> Reichert’s cartilage
- stapes and styloid process of temporal bone
- lesser horns/cornu and superior portion of the hyoid bone
- stylohyoid ligament
What are the skeletal elements of arches 3,4, and 6?
- 3: greater horns/cornu and inferior portion of the hyoid bone
- 4,6: laryngeal cartilages (thyroid, arytenoid, corniculate, cuneiform, and cricoid) except epiglottis
Arteries from arch 1
Maxillary arteries
Arteries arch 2
- stapedial artery
- hyoid artery
Arteries arch 3
- common carotid arteries
- proximal portion of the internal carotid arteries
Arteries arch 4
- connects to aorta forming the aortic arch
- right side forms proximal portion of right subclavian artery
Arteries arch 5
-rudimentary and do not develop into any known vessels
Arteries arch 6
- proximal: right and left pulmonary arteries
- distal: left aortic arch -> ductus arteriosus
What is the derivative of. Pharyngeal cleft 1?
-external auditory meatus
What is the derivatives of pharyngeal cleft 2-4?
Neck
What is the derivative of pharyngeal pouch 1?
- middle ear auditory tube and endoderm forms the lining of the middle ear
- between the first pouch and cleft is the tympanic membrane
What is the derivative of pharyngeal pouch 2?
- supratonsillar fossa
- underneath endoderm of the second pouch develops tonsil are crypts and differentiates into lymphoid tissue called the palatine tonsils
What is the derivative pharyngeal pouch 3?
- thymus
- parathyroid gland
What is the derivative of pharyngeal pouch 4?
- thymus
- parathyroid gland
- ultimobranchial body
What can remnants of pharyngeal clefts 2-4 form?
-can appear in the form of cervical cysts or fistfuls found along the anterior border of the sternocleidomastoid muscle
Cells from the ultimobrachial body differentiate into parafollicular cells (C cells) that produce calcitonin.
: )
What is DiGeorge syndrome?
- micro deletion on DGS critical region on chromosome 22
- characterized by hypoparathyroidism, which results hypocalcemia
- hypoplastic thymus or absent thymus which results in problematic immune system
- conotruncal heart defects
- cleft lip and/or palate
- problems with development and function of the brain
When does the tongue develop?
During the 4th week, anterior and posterior tongue have different mechanism
What does the tongue differentiate from?
-1st, 2nd, 3rd pharyngeal arches and migration of muscles from the occipital somites
-anterior: arises from 1st arch formed from 3 masses (2 lateral lingual swellings and the tuberculum impar)
+lateral; lingual swellings enlarge, merge with each other and overgrow the tuberculum impar to form the oral part of the tongue
How does the base of the tongue develop?
- develops mainly from 3rd arch -> initially indicated by midline elevation that appears behind the tuberculum impar
- tissue from arches 3 and 4 overgrow and second arch to become continuous with the body of the tongue
- the site of union between base and body is the sulcus terminalis
What is the origin, sensory innervation, and taste bud innervation of the anterior two thirds of the tongue?
Origin: median tongue, lateral lingual swellings
Sensory: lingual nerve, branch of trigeminal nerve
Taste bud: facial nerve
Origin, sensory innervation, taste bud innervation of posterior one third of tongue
Origin: hypophyseal eminence
Sensory: glossopharyngeal nerve
taste bud: glossopharyngeal nerve, vagus nerve
How is the thyroid gland formed?
- not derived from any pharyngeal pouches
- arises from midline of thyroid diverticulumthat forms from the endoderm in the flood of the pharynx just caudal to the 1st pharyngeal arch -> differentiate into follicular cells of the thyroid gland
- diverticulum elongates but remains connected to tongue by thyroglossal duct -> is obliterated, foramen cecum in the midline at their terminal sulcus
- endodermal mass of cells invaginate a into underlying mesoderm, creating the thyroid diverticulum that is positioned 2/3 and posterior 1/3 of developing tongues
- thyroid diverticulum grows inferiorly, often between the skeletal elements of the 2nd and 3rd arches
- it then migrates to a position anterior to the upper portion of the developing trachea
What can anomalies in thyroid develop result in?
-ectopic thyroid tissue and/or cysts present along the course of the thyroglossal duct, which is a midline structure
What is a thyroglossal duct fistula?
-thyroglossal duct cyst may rupture and present as a draining sinus, which has been erroneously called a thyroglossal fistula, although communication with foramen cecum is extremely rare
When do the pharyngeal arches appear?
-four weeks of development
