Development Of The Head And Neck Flashcards
The dominant part of the future head region is what?
-the forebrain
The earliest representation of the facial region is what?
-the stomodeum
Much of the tissue involved in the formation of the facial area is derived from where?
Neural crest
What is the frontonasal prominence?
-consists of forebrain neural crest cells and midbrain neural crest cells
What will the ectoderm all nasal placodes form?
-will form nasomedial (from forebrain neural crest) and nasolateral (from midbrain neural crest) processes
Maxillary and mandibular processes filled with ________ ________ __________.
-neural crest mesenchyme
What are the components of the pharyngeal region?
- pharyngeal pouches
- thyroid diverculum
- pharyngeal grooves
- pharyngeal/brachial arches
- aortic arches
What composes the pharyngeal pouches?
-four pairs of lateral endodermal out pockets from the foregut
What composes thyroid diverticulum?
-ventral midline endodermal outpocketings from floor of foregut between pharyngeal pouches I and II
What composes the pharyngeal grooves?
-four pairs of ectodermal inpocketings that lie opposite. To the associated pharyngeal pouches
What composes the pharyngeal/brachial arches?
-five pairs of mesenchymal masses that lie between the pharyngeal pouches and grooves
What composes the aortic arches?
-single artery within each pharyngeal arch that connects the ventral aorta to the dorsal aorta
What are some derivatives of pharyngeal tissues?
- pharyngeal arch derived musculature -> mesoderm from somitomeres
- rest of pharyngeal arch mesenchyme (especially ventral) -> from neural crest
What is the basic signaling center in craniofacial development?
- neural tube and paraxial mesoderm
- segmentation of cranial neural tube occurs as a result of Hox gene expression
- segmentation is carried over onto the neural crest cells
- gives rise to neural crest tissue
What is the role of pharyngeal endoderm in craniofacial development?
- patterning is heavily based on exposure to RA
- first pouch is not dependent on RA but is dependent on Otx2
- second pouch is somewhat dependent on RA
- pouches 3 and 4 are heavily dependent on RA
- pharyngeal arch patterning is not dependent on neural crest
- signals the pre patterning of the cranial ectoderm via FGF-8
The craniofacial region develops mostly from where?
Prechordal area
How do pharyngeal arches signal for craniofacial development?
- depends on signals from pharyngeal pouches
- not depend on neural crest
- Dlx genes heavily influence dorsoventral patterning
- Arch 1 ectoderm uses Edn-1 to signal migrating neural crest cells and influences development of arch 1
What does cranial ectoderm do for craniofacial development?
- signaling from this center is necessary for the development of neural crest derivatives involved in lower face morphogenesis
- ectoderm is pre patterned by FGF-8 signals from pharyngeal endoderm
What does the frontonasal ectodermal zone do?
-induced by Shh from forebrain
-is an ectodermal signal center involving establishment of a dorsoventral gradient of FGF-8 (dorsal) and Shh (ventral)
+involved in shaping tip of snout
What is the facial primordia?
- frontonasal prominence
- nasomedial processes
- nasolateral processes
What is the primordia for the jaws? Where are they derived from?
- maxillary processes -> neural crest derived from forebrain and midbrain
- mandibular processes -> neural crest from midbrain and hindbrain
- Meckel’s cartilage -> neural crest
Subdivisions of first arch into upper and lower jaw primordia is dependent on __________.
Endothelin-1
Describe Meckel’s cartilage.
- slender, elongated cartilaginous rod that develops within the first arch
- the mandible forms around this cartilage
- derivatives include articular and quadrate
Describe the non mammalian temporomandibular joint.
-articulation occurs between quadrate bone (upper) and articular bone (lower)
Describe the mammalian temporomandibular joint.
- synovial joint with an articular disc
- formations involves early expression of Barx-1
- articular surfaces are the temporal bone and the mandibular condyle
- quadrate bone moves into middle ear -> incus
- articular bone moves into middle ear -> malleus
How do the palate form?
- forms between 6-10 weeks and divides the common oronasal cavity into a nasal and oral cavity
- two cavities remain connected in the adult as the pharynx
What is the primordia for the palate?
- median palatine process -> forms primary palate, premaxilla
- lateral palatine processes (paired) -> secondary palate
What is the primordia for the nose?
- nasal placode
- nasal pits
- olfactory epithelium
What is required for the development of the nasal placodes? Where does it develop from?
- requires Pax-6 and retinoids
- develop from anterolateral edges of neural plate (before closure)
Explain where the nasal pits come from and how they develop.
-invaginations of nasal placodes
-surrounded by nasomedial and nasolateral processes
+nasomedial processes form tip and crest of nose + septum
+nasolateral processes form nasal alae
- source of retinoids that stimulate FGF-8 to stimulate proliferation of mesenchyme in nasomedial and nasolateral processes
- deepen to form cavities that eventually become continuous with oral cavity via choanae
- medial areas of nasal capsule gives rise to nasal septum and ethmoid bones
- lateral wall of nasal capsule forms nasal conchae
What do the olfactory epithelium form? What does it develop from and what is required for it to develop?
- forms bipolar neurons that project to olfactory bulb
- gives rise to cells that migrate to hypothalamus and synthesize LHRF
- derived from dorsal epithelium of nasal pits and requires FGF-8
What are the stages of tooth development?
- dental lamina
- tooth bud
- cap stage
-bell stage
+enamel organ -> ameloblasts
+dental papilla -> odontoblasts
-dental sac
Dental lamina stage
-C shaped bands of oral ectoderm overlying neural crest mesenchyme
Tooth bud stage
-epithelial downgrowth overlying neural crest mesenchyme and marking position of a single tooth
Cap stage
-inverted cup shaped layer of ectoderm (ameloblasts layer) capped by stellate reticulum and covering a mass of mesenchyme -> dental papilla
Bell stage
-cone shaped primordium covered by stellate reticulum overlying the enamel organ
What is the enamel organ?
-ameloblasts make up the outermost layer of the two layered covering
What is the dental papilla?
-odontoblasts form the outermost layer of this pulpy mass and lie under and adjacent to the layer of ameloblasts
Dental sac
-a condensation of mesenchymal cells around the developing tooth which will form the cementum and periodontal ligament
What is necessary for development of the tooth past the bud stage?
Pax-9
What forms non-tooth forming spaces?
BMP-4 inhibits FGF-8, creating non tooth forming spaces
How do the salivary glands form?
- arise as typical epithelial exocrine glands from the oral epithelium
- development depends on interactions between the epithelium and the underlying mesenchyme
What does the patterning of the salivary glands depend on?
- Shh
- signaling between Shh and FGF occurs within the epithelium rather than between the epithelium and mesenchyme as occurs in other types of glandular development
