Development Of The Pharyngeal Apparatus Flashcards
Which structures make up the pharyngeal apparatus?
Pharyngeal arches (PA), pouches, grooves (clefts) and membranes
What does the pharyngeal apparatus contribute to?
Formation of nasal cavities, oral cavity, tongue, larynx, pharynx, ear and neck
When do pharyngeal arches develop?
Early in the 4th week as neural crest cells that migrate into the future head and neck
Explain the appearance of the 1st-6th PAs
1st pair (primordial jaws) appear lateral to developing pharynx
Arches 2-4 soon appear as ridges on each side of the future head and neck regions
5/6th arches are rudimentary and not visible on the surface of the embryo
Neural crest cells migrate from which structures?
Forebrain, midbrain and hindbrain (during the 4th week)
What does each PA consist of?
A core of mesoderm and mesenchyme
Each PA is covered by what?
Externally by ectoderm and internally by endoderm
What is mesenchyme?
Embryonic CT derived from migratory NCC
What is head mesoderm?
Mesoderm arising from paraxial mesoderm
Once formed the pharyngeal arches support and give rise to what?
Support the lateral walls of the primitive pharynx
Give rise to facial prominences that contribute to craniofacial mesoderm
What is the stomodeum?
Oral cavity
What are the 4 components of a pharyngeal arch?
NCC-derived mesenchyme, paraxial mesoderm, lateral plate mesoderm and prechordal plate mesoderm
What does NCC-derived mesenchyme form?
Forms all CT in the head including the dermis and smooth muscle
What is the function of paraxial mesoderm in PAs?
Populates each arch to form PA musculature
What is the function of lateral plate mesoderm within PAs?
Angioblasts differentiate into endothelium
What does the prechordal plate mesoderm form within the PAs?
Extraocular musculature
What role does pharyngeal endoderm play?
Plays an essential role in regulating the development of the PA
What are the 4 elements that the PA house?
Cartilaginous rods, muscular component, CNs and arch artery
What does the cartilaginous rod of the PAs form?
Skeletal elements
What does the muscular component of a PA form?
Muscles of the head/neck
The CNs in PA have what components?
Sensory and/or motor components
What does the arch artery within the PA form?
Vasculature of the head/neck
What is Meckel’s cartilage?
Cartilage of the 1st PA
The dorsal portion of the Meckel’s cartilage forms what?
Malleus and incus
Describe Meckel’s cartilage
Bone forms laterally to Meckel’s which disintegrates
What does the ventral part of Meckel’s cartilage form?
The primordium of the mandible
What does the perichondrium of Meckel’s cartilage give rise to?
Anterior ligament of malleus and sphenomandibular L
What is Rierchert’s cartilage?
Cartilage of PA2
What does the dorsal region of Riechert’s cartilage contribute to?
Stapes and styloid of the temporal bone, remainder disintegrates
What does the perichondrium of Riechert’s cartilage form?
Stylohyoid ligament
What does the ventral portion of Riechert’s cartilage form after ossification?
Lesser Cornu/horn of hyoid bone
What does the third arch cartilage become after it ossifies?
Forms greater Cornu of hyoid bone
The body of the hyoid bone is formed by what?
Hypopharyngeal eminence
Prominence in floor of embryonic pharynx (from PA3 and 4)