G56: Dev of Face and Pharynx Flashcards
Week 4
6 pharyngeal arches at rostal end
arch 4-6 fuse and 5
is only seen transiently
Pharyngeal arches/grooves are lined with
ectoderm (outer surface)
Pharyngeal pouches are lined with
endoderm (inner wall of pharynx)
Pharyngeal membrane
separates pouches and grooves; lined with an outer layer of ectoderm and inner layer of endoderm
Paraxial mesoderm forms
CT, skeleton of posterior cranial vault and base, skeletal muscles of face
AT week 4, neural crest cells invade to form
bones of face, thyroid and cricoid cartilage, middle ear, frontal cranial vault and base
Each arch has
- Mesenchymal core
- aortic arch
- cartilaginous rod for skeleton of arch
- myoblasts for head and neck muscles
- CN 5, 7, 9, 10
Brachial motorfibers
refer to fibers that supply skeletal muscle derived from pharyngeal arches (not somites)
Arch 1
Mandibular Arch; maxillary and mandibular processes - maxilla, zygomatic, temporal bone and mandible respectively
Cartilage of Arch 1
Meckel’s cartilage: template for mandibular bone to form around, disappears and mandible forms in place
Meckel’s cartilage that persists becomes
anterior ligament of malleus, sphenomandibular ligament, malleus, incus (endochondral ossification)
Arch 1 muscle derivatives
muscles of MASTICATION, temporalis, masseter, pterygoids, tensor tympani, tensor veli palatini anterior belly of digastric, mylohyoid
What nerve innervates all muscles of ARCH 1?
Trigeminal
Treacher Collins Syndrome
underdevelopment of arch 1, underdeveloped zygomatic bones, mandibular hypoplasia, malformed external ears, inherited or teratogens
disrupts neural crest cell migration
Arch 2
Hyoid Arch; hyoid bone
Cartilage of Arch 2
Reichert’s Cartilage- upper part of hyoid bone, stylohyoid ligament, styloid process of temporal bone and stapes of middle ear
Muscles of Arch 2
Muscles of FACIAL EXPRESSION; posterior belly of digastric, stapedius m, stylohyoid
Cranial nerve associated with Arch2?
Facial n, sensory to tongue, motor to facial expression, visceral motor, general sensory to ear
Arche 3
greater horn of hyoid bone; stylopharyngeus m
Arch 4-6 derivatives
do not form bone, rather persist as cartilage (thyroid, cricoid, arytenoids, corniculate, cuneiform); Pharynx muscles: pharyngeal constrictor, crirocricoid m, levator veli palatine, intrinsic muscles of larynx
Nerve of Arch 3
Glossopharyngeal
Nerve of Arch 4-6
Vagus n
Pharyngeal pouch 1
pharynx to middle ear (tubotympanic recess) which will become the auditory tube, middle ear cavity and mastoid antrum
Pharyngeal pouch 2
forms tonsillar fossa; migrating mesoderm forms tonsils within fossa
Pharyngeal pouch 3
Dorsal and ventral wings; Dorsal wing: inferior parathyroid gland, ventral wing: thymus
Pharyngeal pouch 4
forms the superior parathyroid gland; ventral part of pouch 4: ultimobranchial bodies
Ultimobranchial bodies of ventral pouch 4
are incorporated into thyroid gland to become parafollicular cells (Calcitonin secreting)
Pharyngeal groove 1
external auditory meatus (ectoderm)
Pharyngeal groove 2-5
overgrowth from arch, no persistent meatus. Grooves briefly form a small sinus (cervical sinus) but its obliterated
Tympanic membrane
as arch 1 groove migrates inward and arch 1 pouch migrates outward they meet and form the tympanic membrane (endoderm internally and ectoderm externally)
DiGeorge Syndrome
congenital absence of the thymus and parathyroid glands along with facial abnormalities. (pouch 3)
Persistent Cervical sinus from groove 2-5
(Ectodermally lined cyst) forms a cyst or fistula along the border of sternocleidomastoid or into the pharynx (internal or external branchial fistula)
Tongue week 5 dev
Arch 1: lateral lingual swellings, tuberculum impar (ant 2/3) CN 5
Arch 2-4: Copula (post 1/2 and epiglottis) CN9-10
Arch 2 mostly regresses CN7
Intrinsic muscles of the tongue
come from the occipital region and migrate into tongue region and drag innervation with them
Thyroid development
proliferation of endoderm on dorsum of tongue; foramen ceacum: thyroid diverticulum
Thyroid diverticulum descends
inferiorly down neck, persistent thyroglossal duct or small part persists: pyramidal lobe, and ectopic glandular tissue
Development of face (5 mesenchymal prominences)
5 mesenchymal prominences surrounding the stomodeum: Frontonasal, paired maxillary, and paried mandibular
Frontonasal prominence derivatives
covers developing forebrain; frontal bones, bridge of nose, nasal septum, primary palate, upper incisors
Maxillary prominence derivatives
Sup. arch 1: maxilla, upper cheeks, post-incisor maxillary teeth, secondary plate
Mandibular prominences derivatives
Inf. arch 1: mandible, lower cheeks, mandibular teeth
Frontonasal prominence development
nasal placodes (paired ectodermal thickening) -> nasal pits with medial and lateral nasal prominence surrounding it (mesenchyme), medial nasal prominence fuses at midline to give intermaxillary segment
Maxillary prominence
gives rise to palatine processes that will fuse to form secondary palate
Intermaxillary segment gives rise to
primary hard palate (from medial nasal prominence)
Lateral nasal prominences
alae of the nose; separated from maxillary prominence by the nasolacrimal groove
Nasolacrimal groove invaginates to form the
nasolacrimal duct, and the lateral nasal prominences fuse with maxillary prominences
Mandibular prominences
fuse at midline to form the mandible
Orofacial clefting anomalies
incomplete fusion of facial primordia, nasolacrimal duct
Palatogenesis
Primary palate 4 incisors and incisor foramen, secondary palate is the rest
Median palatal process (pre maxilla)
primary palate forms from the intermaxillary segment from frontonasal prominence
Paired maxillary prominences
develop palatine processes, grow medial and fuse at midline to form SECONDARY PALATE (hard palate) Nasal septum (frontonasal) fuses with primary palate
Orofacial clefting anomaly risk factors
genetics, syndromes, envrinoment (smoking, RA, maternal disease)
Anterior cleft lip and anterior palate anomaly
mesenchyme deficiency in maxillary prominences and median nasal prominences only affecting the primary palate
Posterior cleft palate anomaly
defective secondary palate, prevents lateral palatine processes from growing and fusing (palatine shelf defect)
Complete Cleft lip and palate
both primary and secondary palate are deformed
