QUIZ I General Embryology Flashcards
1
Q
what is embryology?
A
the study of prenatal development
2
Q
what is prenatal development?
A
begins with the start of pregnancy and continues until birth
3
Q
what trimesters do the preimplantation, embryonic, and fetal periods make up?
A
- preimplantation and embryonic periods - first trimester
- fetal period - second and third trimesters
4
Q
each craniofacial structure has what?
A
a primordium - the earliest indication of a tissue or an organ during prenatal development
5
Q
what are the steps of development from the zygote to the fetus?
A
zygote → blastocyst → blastocyst to disc → disc to embryo → fetus
6
Q
when do the major events of prenatal development occur?
A
first, second, third, and fourth weeks
7
Q
describe the general steps of prenatal development
A
- fertilization and formation of the zygote
- mitosis leads to formation of the blastocyst, which forms a fluid filled vesicle and implants in the uterine wall
- the blastocyst gives way to a disc and begins to differentiate into 3 distinct germ layers
- these germ layers form the embryo and ultimately, fetus
8
Q
describe factors driving development
A
- growth factors and cell adhesion molecules act through signaling complexes which activate various transcription factors, affecting cellular changes
- changes might be proliferation, differentiation, or apoptosis
9
Q
growth factors driving development can act through which modes of action?
A
autocrine, paracrine, or endocrine
10
Q
___ is a critical growth factor in craniofacial development
A
bone morphogenic protein (BMP)
11
Q
at gastrulation, BMP switches between ___ vs ___ fate
A
epidermal vs. neural fate
12
Q
what are the functions of BMP?
A
- induction, formation, determination, and migration of neural crest cells
- patterning and formation of facial primordia
- craniofacial skeletogenesis (later roles in maintenance)
- negative regulator of myogenesis (makes bone instead of muscles)
- regulator of early tooth morphogenesis and differentiation
13
Q
what are 4 types of genes involved in the control of embryonic formation?
A
- HOX genes
- Msx genes
- DIx genes
- Shh (sonic hedgehog) genes
14
Q
what is the function of HOX genes?
A
function in patterning the body axis and determine where limbs and other body segments will grown in developing foetus
15
Q
what is the function of Msx genes?
A
control cellular process of differentiation and proliferation during development
16
Q
what is the function of DIx genes?
A
- control development of ectodermal tissues derived from lateral border of the neural plate
- control patterning of the branchial arch skeleton
- also expressed in developing bone and regulate limb development
17
Q
what is the function of Shh genes?
A
play an important role in early induction of facial primordium
18
Q
what do homeobox genes code for?
A
- transcription factors that begin to make cells pattern into one tissue/organ type or another
19
Q
homeobox genes are involved in ___ ___ during embryonic development
A
bodily segmentation
20
Q
homeobox genes are key regulators of what?
A
embryogenesis
help regulate which end is going to be which
21
Q
what type of DNA sequence is the homeobox gene?
A
180 bp DNA sequence
homeodomain in protein
22
Q
___ genes typically switch on cascades of other genes
A
homeobox
23
Q
what type of cell adhesion molecules do neurectoderm and skin ectoderm progenitors express?
A
- neurectoderm
- N-CAM
- skin ectoderm
- L-CAM
24
Q
____ is hugely important for positioning and differentiating
A
cell-cell contact
25
cell adhesion molecules are responsible for what?
specific cell aggregation and sorting
26
which cell adhesion molecules are calcium dependent? calcium independent?
* calcium dependent
* cadherins
* calcium independent
* CAM
27
describe the fertilization phase of the preimplantation period
* first period of prenatal development; occurs during the first week after conception
* ovum is penetrated by sperm
* fusion of 2 haploid gametes gives the full diploid complement of 46 (zygote)
* cell division (mitosis) occurs to form the blastocyst
28
many human disorders can be traced to changes in what?
structures or number of chromosomes
29
describe the cleavage phase of the preimplantation period
* occurs after fertilization when the zygote undergoes mitosis (aka individual cell division or cleavage)
* morula (solid ball) is formed after initial cleavage
* zygote becomes blastocyst
* further mitotis cleavages, with little to no differentiation involved
* lasts until 3 distinct germ layers have formed
30
describe implantation
* blastocyst stops traveling by the end of the first week
* it implants in the endometrium
* implantation
* typically on the back wall
31
list the summary of events during the first week after fertilization
* rapid proliferation
* migraiton of cells
* realignment of cells
* fluid filled cavity
* embryoblast (inner cell mass)
* forms the embryo proper
* trophoblast
* implantation/placenta
32
when does the embryonic period occur?
beginning of week 2 to the end of week 8
33
what occurs during the embryonic period?
* important spatial and temporal events called patterning
* includes formation of the pharyngeal arches, somite development, face development, palate and tongue formation, and other critical events
34
describe patterning during the embryonic phase
* key process in normal development
* axial specification (which end is up)
* segmentation (what forms between each end)
* tissue and organ specialization and formation begins
* development of dentition begins
* regional development of incisors, canines, pre-molars, and molars
35
what 5 steps are involved in the developmental process in the embryo?
* induction
* proliferation
* differentiation
* morphogenesis
* maturation
36
describe induction
when one group of cells tells another group of cells (competent cells) to do something
37
describe proliferation
cell division, increase in number and accumulation of cell productions
38
describe differentiation
development of specific structures and/or functions by individual cells or group of cells
39
describe morphogenesis
cell migration, interactions and proliferations causing the development of specific structures
40
describe maturation
attainment of adult size and function from proliferation, differentiation, and morphogenesis
41
what is gastrulation?
* the formation of the 3 germ layers
* ectoderm, mesoderm, and endoderm
* takes place around week 3
42
what is the bilaminar germ disc?
* after the blastocyst implants, the embryoblast differentiates into two layers
* dorsal cells (epiblast layer)
* ventral cells (hypoblast layer)
* establishment of embryo axis (which direction will be which)
43
describe the layers of the bilaminar germ disc
* dorsal cells (epiblast layer)
* reorganize to form amniotic cavity
* superior, high columnar cells
* ventral cells (hypoblast layer)
* form the roof of the secondary yolk sac
* inferior, small cuboidal cells
44
what is the primitive streak?
* after the formation of the bilaminar disc, the primitive streak forms
* little groove formed by epiblast cells, which proliferate to bulge out to either side of the groove
* defines the future bilateral symmetry along a rostral-caudal axis
* prochordal plate forms at the rostral end, where the ectoderm curves around integrates with the endoderm
45
describe the process of gastrulation
* ectodermal cells invaginate at the primitive node, forming the primitive pit
* cells migrate between ectoderm and endoderm
* the notochord forms (vertebral precursor)
* epiblast cells (future ectoderm) divide, migrate, and invaginate, spreading laterally between the two layers to form the mesoderm
* mesoblast cells form true embryonic endoderm and mesoderm
46
the notochord and mesoderm totally separate the ectoderm and endoderm everywhere except ___ and \_\_\_
prochordal plate and the cecal plate (the other end)
47
describe formation of the mesoderm
* medial epiblast cells lose their cell-cell adhesions, become motile, and invade inwards
* these mesenchymal cells are interspersed in matrix and have no polarity
* chane in cell attachment proteins from E to N cadherin
48
the formation of the mesoderm is important in tooth development. why?
epithelial cells and mesenchymal cells have to talk to one another to make enamel (epithelial) and dentin/pulp (mesenchymal)
49
describe the triploblastic embryo
* after the mesoderm is formed, we have a disc with 3 layers and a cephalic end defined by the prochordal plate, and folding can occur
* the head fold is going to form the oropharyngeal (buccopharyngeal) membrane at the prochordal plate end
* no mesoderm between ectoderm and endoderm
* location of the stomodeum (primitive mouth) will be here
50
what do ectodermal cells give rise to?
* nervous system
* epidermis and its appendages (hair, nails, sebaceous glands, sweat glands)
* epithelium lining the oral cavity, nasal cavities, and sinuses
* part of the intraoral glands
* tooth enamel
51
what do endodermal cells give rise to?
epithelial lining of the respiratory and gastrointestinal tract and all associated organs
52
what do mesodermal (mesenchymal) cells give rise to?
* muscles and all the structures derived from the connective tissue
* bone, cartilage, blood, dentin\*, pulp\*, cementum\*, and the periodontal ligaments\*
* \*neural crest
53
after week 3, and gastrulation occurs, which 3 key events take place?
1. differentiation of the nervous system
2. formation/migration of the neural crest
3. embryo folding: head fold, lateral folds, and tail fold
54
describe embryonic folding
* onset of folding is at 24 days
* imagine a flat plate forming a tube (primitive nervous system) and moving that tube down inside a continually forming body of cells
55
what is the neuroectoderm?
a specialized group of cells that differentiates from the ectoderm
56
describe nervous system formation
* formation of neuroectoderm
* localized to the neural plate of the embryo from the cephalic end to the caudal end
* neural plate - central band of cells that extends the length of the embryo
* plate undergoes further growth and thickening, causing it to deepend and invaginate inward, forming the neural groove
57
where does the neural tube closure occur?
neural fold fusion begins at the upper cervical levels and proceeds both rostrally and caudally
58
neural tube closure is a critical point in development. what can result if neural tube closure is incomplete?
spina bifida
59
what is the fate of paraxial mesoderm?
cartilage, segmented muscle
60
what is the fate of intermediate mesoderm?
kidneys, gonads
61
what is the fate of the lateral plate mesoderm?
heart, gut
62
differentiated mesoderm gives rise to the ___ that are located on the sides of the developing central nervous system
somites
63
describe formation of the "head"
* neural tube expands to form the forebrain, midbrain, and hindbrain
* hindbrain segments into rhombomeres which express Hox genes
* branchial arches develop
64
the neural crest develops from what, and during which week?
develops from the neuroectoderm during the 3rd week
65
describe neural crest migration
* after it is formed, it migrates away from the crests of the neural folds and disperses in mesenchyme
* so, some cells in the mesenchyme are derived from the neuroectoderm
* migrates widely and contributes to many structures
66
sometimes, mesenchyme will be described as ___ because of its origins
ectomesenchyme
67
where does dental pulp and dentin come from?
neural crest tissue
68
what is treacher collins syndrome?
* aka mandibulofacial dysostosis
* failure of neural crest cells to migrate to the facial region
69
in embryo folding, the head fold is critical to the formation of what?
the oral cavity
70
embryo folding ultimately determines the final disposition of what?
ectoderm, mesoderm, and endoderm
71
describe the development of the pharynx
* stomodeum (primitive mouth) remains separate, but will ultimately break down to form the oral opening of the GI tract
* the foregut gives rise to the primitive pharynx
* the structure will ultimately form the oropharynx
72
when does the fetal period occur?
week 9 (3rd month) to birth
73
what occurs during the fetal period?
* the basic tissues and structures are mainly formed
* a matter of growth and continued specialization
* maturation of existing structures occurs as the embryo enlarges, becoming a fetus
* physiological process of maturation of the individual tissue types and organs
* proliferation, differentiation, and morphogenesis
