Embryology of the Pharyngeal Apparatus Flashcards
Pharyngeal arch development
Develop in early 4th week as neural crest cells, migrate into the future head and neck
1st pair of arches- primordial jaws, appear lateral to developing pharynx
Arches 2-4 soon appear as ridges on each side of the future head and neck regions
5th and 6th arches- rudimentary and not visible on surface of embryo
Arches consists of
Core of mesoderm with ectoderm covering and endoderm internally
Mesenchyme is derived from ___ while head mesoderm forms ___
Mesenchyme derived from migrating neural crest cells and forms all CT in the head
Head mesoderm forms paraxial mesoderm which populates each arch to form musculature
Pharyngeal arch functions
Support the lateral wall of the primordial pharynx
Give rise to prominences of tissue that contribute to craniofacial development
What forms the endothelium
Lateral plate mesoderm gives rise to angioblasts that differentiate into endothelium
What forms the extraocular musculature
Prechordal plate mesoderm
What plays an important role in regulating the development of the arches
Pharyngeal endoderm!!
Structures contained in pharyngeal arches
Cartilaginous rod- forms skeletal elements
Muscular component- forms head/neck muscles
Cranial nerves
Arch artery- derived from truncus arteriosus/aortic sac of primordial heart, enters dorsal aorta
Meckels cartilage
Cartilage of arch 1
Dorsal portion forms malleus and incus
Perichondrium forms anterior ligament of malleus and sphenomandibular ligament
Ventral parts form primordium of mandible
Riecherts cartilage
Cartilage of arch 2
Dorsal region contributes to stapes and styloid process of temporal bone
Perichondrium forms stylohyoid ligament
Ventral end ossifies and forms lesser cornu/horn of hyoid bone
Third arch cartilage
Forms greater cornu of hyoid bone
Body of hyoid is formed by hypopharyngeal eminence- a prominence in floor of embryonic pharynx from 3/4 arches
4th arch cartilage
Laryngeal cartilages including epiglottis (NCC derived)
6th arch cartilage
Laryngeal cartilages, but origin is uncertain
What forms musculature of pharyngeal arch
Paraxial mesoderm and prechordal plate (ocular muscles)
First arch muscles and derived from what
Muscles of mastication Mylohyoid Anterior belly of digastric Tensor veli palatini Tensor tympani Head mesoderm
Second arch muscles and derived from what
Stapedius and muscles of facial expression
Posterior belly of digastric
Stylohyoid
Head mesoderm
Third arch muscles and derived from what
Stylopharyngeus
Head mesoderm
Fourth arch muscles and derived from what
Cricothyroid
Levator veli palatine
Constrictors of pharynx
Occipital somites
Sixth arch muscles and derived from what
Intrinsic muscles of larynx
Occipital somites
Trigeminal nerve supplies
First arch
Principle sensory for head and neck
Motor nerve for mastication muscles
Facial nerve supplies
Second arch
Muscles of facial expression
Glossopharyngeal nerve supplies
Third arch
Stylopharyngeus
Vagus nerve supplies
4th-6th arches
4th supplied by superior laryngeal branch and its recurrent laryngeal branch
Constrictors of pharynx and intrinsic muscles of larynx supplied by vagus
Arch artery
5 pairs of arteries forming basket like structure, each arise from aortic sac and connect to dorsal aorta
First pharyngeal groove
Forms external acoustic meatus
Pharyngeal grooves are externally located b/w pharyngeal arches
Grooves consist of ectoderm
Grooves 2-4 lie where
Cervical sinus
Pharyngeal pouches
Line the pharynx internally
Cervical cysts
Branchial abnormality
Remnants of cervical sinus and/or 2nd groove
Persist and form a slowly enlarging, painless, free lying cyst in the neck, inferior to angle of the mandible
Accumulation of fluid and cellular debris derived from desquamation of their epithelial linings
Cervical sinus
Branchial abnormality
Failure of the 2nd pharyngeal arch groove and cervical sinus to obliterate
Detected due to discharge of mucus
Typically bilateral and commonly associated with auricular sinuses
Cervical fistula
Branchial abnormality
Abnormal canal that opens into the tonsillar sinus and externally in the side of the neck
Persistence of parts of 2nd groove/pouch
First pharyngeal membrane forms
Pharyngeal membranes formed where pouch endoderm contacts groove ectoderm
Pharyngeal membranes are quickly infiltrated by mesenchyme
Forms tympanic membrane
First pharyngeal pouch forms
Tubotympanic recess- tympanic cavity and mastoid antrum
Pharyngotympanic tube
Endoderm contacts first pharyngeal groove and contributes to tympanic membrane
Pouches are endoderm
Second pharyngeal pouch forms
Portion of it forms tonsillar sinus
Endoderm proliferates and forms tonsillar epithelium
Mesenchyme differentiates into lymphoid nodules of palatine tonsil
Third pharyngeal pouch forms
Dorsal portion differentiates into inferior parathyroid gland
Ventral portions form thymus
Caudally migrate due to growth of brain/cardiac regions
Fourth pharyngeal pouch forms
Dorsal portion forms superior parathyroid glands
Forms ultimobranchial body which fuses with thyroid gland and gives rise to parafollicular cells
Thymus development
Develops from PA3 endoderm, comprised of epithelial cords
Function of epithelial cords in thymus development
Grow into surrounding mesenchyme to form thymic lobules
Become arranged around a central point to form thymic corpuscles
Form an epithelial reticulum for housing lymphocytes
Thyroid gland development
First endocrine gland to develop ~24 days
Forms a median endodermal thickening in floor of primordial pharynx
Descends in the neck with tongue growth and passes ventral to developing hyoid bone and laryngeal cartilages
Connected to tongue by thyroglossal duct
First pharyngeal arch syndrome
Abnormal development of components of PA1
Malformation of eyes, ears, mandible, palate
Multiple different manifestations and causes, each with different names discussed in next cards
Results from insufficient migration of NCC into 1st arch during 4th week
Treacher-Collins syndrome (mandibulofacial dysostosis)
Malar hypoplasia w/down slanting palpebral fissures, defects of lower eyelids, deformed external ears and sometimes middle/internal ears
Autosomal dominant
Mutation in gene that encodes for TREACLE protein, involved in ribosome biogenesis
Truncation mutation
Pierre Robin sequence
Occurs de novo
Associated with hypoplasia of mandible, cleft palate and defects in eyes and ears
Initiating defect is small mandible (micrognathia), results in posterior displacement of the tongue and obstruction of full closure of the palate which results in bilateral cleft palate
Thyroid hemiagenesis
Unilateral failure of formation, left lobe is more commonly absent
Mutations in receptor for TSH is usually involved
DiGeorge syndrome
Breakdown of signaling from PA endoderm to NCC
Agenesis of thymus and parathyroid glands
Congenital hypoparathyroidism
Shortened philtrum of upper lip, low set and notched ears
Nasal clefts, thyroid hypoplasia
Cardiac abnormalities
Arch arteries for PA1-PA3
PA1- terminal branch of maxillary artery
PA2- stapedial artery (embryonic), caroticotympanic artery (adult)
PA3- common carotid artery, root of internal carotid
Arch arteries for PA4
Arch of aorta- left side
Right subclavian artery- right side
Original sprouts of pulmonary arteries
Arch arteries for PA6
Ductus arteriosus
Roots of definitive pulmonary arteries
