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Growth and Development > Head and Neck Development > Flashcards

Head and Neck Development Flashcards

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1
Q

what do genes (DNA) encode

A

RNA and proteins

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2
Q

what does RNA and protein define

A

the identity of each cell- its appearance and how it behaves

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3
Q

what does gene mutation and differences in non genetic instructions determine

A

phenotype

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4
Q

what is the difference between epithelia and mesenchyme

A
  • epithelial cells are tightly bound to each other in sheets and are not motile
  • mesenchymal cells are surrounded by ECM and are very motile
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5
Q

what are the embryonic germ layer

A
  • ectoderm
  • mesoderm
  • endoderm
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6
Q

what are the axes that define the craniofacial complex

A
  • left- right
  • dorsal- ventral
  • anterior- posterior
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7
Q

clinical treatments always consider:

A
  • form
  • symmetry
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8
Q

describe the embryo during the first three weeks

A
  • zygote -> 2 cell -> 4 cell -> 8 cell -> morula -> blastocyst -> late hatched blastocyst -> implantation -> carnegie stage 5 -> carnegie stage 7-9
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9
Q

what axis is apparent in the first three weeks

A

dorsal ventral axxis

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10
Q

is the D-V axis established as a consequence of cavitation and formation of the inner cell mass or is it determined earlier

A

determined earlier

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11
Q

what is visible in the blastocyst stage

A

inner cell mass

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12
Q

when are the A-P and L-R axes determined

A

at the start of week 3 with the appearance of the primitive streak

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13
Q

where do epiblastic cells converge

A

at the midline and ingress

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14
Q

what marks the posterior end

A

epiblastic cells

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15
Q

what does the appearance of the primitive streak define

A

the A-P and L-R axes

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16
Q

the primitive streak progressively elongates along the midline through the process of _____

A

convergent extension

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17
Q

what do cells of the epiblast layer migrate through and form

A

migrate through primitive streak to form mesoderm and embryonic gut endoderm

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18
Q

what happens in gastrulation

A

-epithelial to mesenchyme transformation to form mesoderm
- movement of epiblast (ectoderm) to form embryonic endoderm - both epithelia

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19
Q

describe the disproportionate growth of the germ layers

A

greater proliferation of epiblast (ectoderm) because it also generates all mesoderm and embryonic endoderm

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20
Q

describe the node

A

anterior most end (ventral side) of primitive streak is unique in both appearance and function

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21
Q

what animals have the node

A

all vertebrates

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22
Q

what is the node essential for

A
  • patterning and induction of embryonic cells ( mesoderm and embryonic endoderm)
  • establishment of left right symmetry
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23
Q

factors secreted by cells of the node that induce anteriorly migrating mesoderm to form:

A
  • the prechordal plate
  • the notochord
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24
Q

what is the prechordal plate and where is it located

A
  • provides the signals for induction of head structures
  • most anterior region of mesoderm
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25
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
26
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
27
how is molecular asymmetry established
- asymmetric expression of morphogenetic factors such as SHH, BMP4 and FGF8 around node
28
what do morphogenetic factors around the node do
initiate cascade of gene expression to promote asymmetric specialisation/ commitment of mesoderm
29
nodal cells each have one _____
motile cilium
30
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
31
what are the possible properties of the cilium
mechanosensory or rotational
32
how long does the rotational beat in nodal cilia last
for a few hours
33
what does the rotational beat in nodal cilia do
generates leftward flow, resulting in asymmetric distribution of morphogens/ growth factors
34
describe the prevalance of organ asymmetry
reproducible morphological and functional asymmetries in nearly all internal organs - present in all vertebrates
35
what is normal organ asymmetry also called
situs solitus
36
what is the condition of inverted L-R organs called
situs inversus
37
what do the nodal cilia control
organ asymmetry
38
what is neural tube formation called
neurulation
39
what is neurulation a precursor to
brain and spinal cord
40
how is the neural plate formed
factors from the mesoderm induce thickening of overlying ectoderm which turns into the neural plate
41
what do signals from notochord do
induce a hinge point (floor plate) to help drive folding
42
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
43
advanced maturity of anterior end =??
expanded neural plate -> future brain
44
how does the neural tube close
proceeds anteriorly and posteriorly from the mid region
45
by the end of week 3 the head and neck region comprises about _______ of the embryo
half
46
what are the possible defects in neural tube closure
spina bifida (common, viable)
47
what is head formation called
cephalization
48
what serves at the hinge point during cephalization
the oropharyngeal membrane
49
when does embryonic folding occur
-while cephalization occurs - while pharyngeal arches form
50
what structures become specialized during embryonic folding
foregut and hindgut
51
what are neural crest cells
a unique population of pluripotent stem like cells originating at the crest of the enclosing neural tube
52
how do neural crest cells migrate
ventro laterally to populate the ventral side of the embryo
53
what process are neural crest cells generated by
epithelial mesenchymal transformation which is analagous to that generating the third germ layer (mesoderm)
54
what is happening during EMT
cells transform from epithelial type to mesenchymal phenotype
55
what does cranial neural crest cells drive
outgrowth of the primitive tissue masses that will form much of the head and neck - pharyngeal arches
56
what are cranial neural crest cells a major contributor to
craniofacial structure and specifcially to mineralized tissues of the oral region
57
when is the fate of CNCC determiend
prior to departure from neural tube
58
what are the multiple visible constrictions in the neural tube
rhombomeres 1-8, the diencephalon and anterior mesencephalon
59
what do the visible constrictions in the neural tube define
distinct populations of the CNCC and their route of migration into early facial tissue
60
what are the CNCC derivatives
mesectodermal cells: skeleton, connective tissue, muscle
61
early molecule patterning during gastrulation enables _______
later coordinated tissue morphogenesis
62
embryogenesis is a _____process. Not _____
generative; descriptive
63
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
64
what is also called the second wave of development
CNCC migration

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