Head and Neck Development Flashcards
what do genes (DNA) encode
RNA and proteins
what does RNA and protein define
the identity of each cell- its appearance and how it behaves
what does gene mutation and differences in non genetic instructions determine
phenotype
what is the difference between epithelia and mesenchyme
- epithelial cells are tightly bound to each other in sheets and are not motile
- mesenchymal cells are surrounded by ECM and are very motile
what are the embryonic germ layer
- ectoderm
- mesoderm
- endoderm
what are the axes that define the craniofacial complex
- left- right
- dorsal- ventral
- anterior- posterior
clinical treatments always consider:
- form
- symmetry
describe the embryo during the first three weeks
- zygote -> 2 cell -> 4 cell -> 8 cell -> morula -> blastocyst -> late hatched blastocyst -> implantation -> carnegie stage 5 -> carnegie stage 7-9
what axis is apparent in the first three weeks
dorsal ventral axxis
is the D-V axis established as a consequence of cavitation and formation of the inner cell mass or is it determined earlier
determined earlier
what is visible in the blastocyst stage
inner cell mass
when are the A-P and L-R axes determined
at the start of week 3 with the appearance of the primitive streak
where do epiblastic cells converge
at the midline and ingress
what marks the posterior end
epiblastic cells
what does the appearance of the primitive streak define
the A-P and L-R axes
the primitive streak progressively elongates along the midline through the process of _____
convergent extension
what do cells of the epiblast layer migrate through and form
migrate through primitive streak to form mesoderm and embryonic gut endoderm
what happens in gastrulation
-epithelial to mesenchyme transformation to form mesoderm
- movement of epiblast (ectoderm) to form embryonic endoderm - both epithelia
describe the disproportionate growth of the germ layers
greater proliferation of epiblast (ectoderm) because it also generates all mesoderm and embryonic endoderm
describe the node
anterior most end (ventral side) of primitive streak is unique in both appearance and function
what animals have the node
all vertebrates
what is the node essential for
- patterning and induction of embryonic cells ( mesoderm and embryonic endoderm)
- establishment of left right symmetry
factors secreted by cells of the node that induce anteriorly migrating mesoderm to form:
- the prechordal plate
- the notochord
what is the prechordal plate and where is it located
- provides the signals for induction of head structures
- most anterior region of mesoderm
what is the notochord and where is it located
- provides the signals for induction of the neural plate
- transient epithelial like rod structure along the midline
how does the node induce the body axis
- specifies the fate of the mesoderm as it is formed
- creation of asymmetry in symmetrical embryo
- first establishes molecular asymmetry
-conversion into asymmetric organogenesis
how is molecular asymmetry established
- asymmetric expression of morphogenetic factors such as SHH, BMP4 and FGF8 around node
what do morphogenetic factors around the node do
initiate cascade of gene expression to promote asymmetric specialisation/ commitment of mesoderm
nodal cells each have one _____
motile cilium
what is a cilium
a membrane covered extension from the cell that has a microtubule cytoskeleton core which helps define the properties of the cilium
what are the possible properties of the cilium
mechanosensory or rotational
how long does the rotational beat in nodal cilia last
for a few hours
what does the rotational beat in nodal cilia do
generates leftward flow, resulting in asymmetric distribution of morphogens/ growth factors
describe the prevalance of organ asymmetry
reproducible morphological and functional asymmetries in nearly all internal organs
- present in all vertebrates
what is normal organ asymmetry also called
situs solitus
what is the condition of inverted L-R organs called
situs inversus
what do the nodal cilia control
organ asymmetry
what is neural tube formation called
neurulation
what is neurulation a precursor to
brain and spinal cord
how is the neural plate formed
factors from the mesoderm induce thickening of overlying ectoderm which turns into the neural plate
what do signals from notochord do
induce a hinge point (floor plate) to help drive folding
describe anterior (head) specification
the morphological difference of the anterior most region of the neural tube reflects unique cellular identities and thus different inductive cues
advanced maturity of anterior end =??
expanded neural plate -> future brain
how does the neural tube close
proceeds anteriorly and posteriorly from the mid region
by the end of week 3 the head and neck region comprises about _______ of the embryo
half
what are the possible defects in neural tube closure
spina bifida (common, viable)
what is head formation called
cephalization
what serves at the hinge point during cephalization
the oropharyngeal membrane
when does embryonic folding occur
-while cephalization occurs
- while pharyngeal arches form
what structures become specialized during embryonic folding
foregut and hindgut
what are neural crest cells
a unique population of pluripotent stem like cells originating at the crest of the enclosing neural tube
how do neural crest cells migrate
ventro laterally to populate the ventral side of the embryo
what process are neural crest cells generated by
epithelial mesenchymal transformation which is analagous to that generating the third germ layer (mesoderm)
what is happening during EMT
cells transform from epithelial type to mesenchymal phenotype
what does cranial neural crest cells drive
outgrowth of the primitive tissue masses that will form much of the head and neck
- pharyngeal arches
what are cranial neural crest cells a major contributor to
craniofacial structure and specifcially to mineralized tissues of the oral region
when is the fate of CNCC determiend
prior to departure from neural tube
what are the multiple visible constrictions in the neural tube
rhombomeres 1-8, the diencephalon and anterior mesencephalon
what do the visible constrictions in the neural tube define
distinct populations of the CNCC and their route of migration into early facial tissue
what are the CNCC derivatives
mesectodermal cells: skeleton, connective tissue, muscle
early molecule patterning during gastrulation enables _______
later coordinated tissue morphogenesis
embryogenesis is a _____process. Not _____
generative; descriptive
what can malformation and normal phenotypic variation result from
-single changes in gene sequence
- combinations of normal gene variants
- changes in the environment to which cells respond
what is also called the second wave of development
CNCC migration
