B8.031 Embryogenesis Flashcards
1
Q
fertilization and implantation time frame
A
weeks 1-2
blastocyst normally implants in uterus
2
Q
embryonic period
A
week 3-8
in first 8 weeks, embryos progress from a single cell to having established organ primordia and “recognizable” external body form
3
Q
fetal period
A
week 9-birth (40)
4
Q
extraembryonic membrane formation (big picture)
A
membranes protect and nurture the developing embryo; function in gas & waste exchange
shock absorber
5
Q
placentation (big picture)
A
placenta formation nutrition and waste exchange with embryo
6
Q
gastrulation (big picture)
A
forms 3 germ layers, which give rise to body structures via cell proliferation, migration, differentiation, and morphogenesis (big scale movement of tissues)
7
Q
cardiovascular development and hematopoiesis (big picture)
A
oxygenation and nutrition (along with placenta)
blood cell formation
8
Q
neurulation (big picture)
A
formation of the nervous system
9
Q
when does implantation occur
A
5.5-6 days
10
Q
what cavities are present in the developing embryo at the end of the 2nd month
A
amniotic
chorionic
yolk sac
uterine
11
Q
blastocyst development at day 4.5 to 5
A
composed of:
1. outer cell mass = trophoblast cells
2. inner cell mass = embyoblast, localized to one pole
fluid penetration into intercellular spaces of ICM results in blastocele cavity
12
Q
2 layers of embryoblast
A
epiblast (upper)
hypoblast (lower)
13
Q
cavities present in blastocyst at day 7.5
A
blastocyst and amniotic cavities
14
Q
structure of epiblast
A
high columnar cells adjacent to amniotic cavity
15
Q
amnioblasts
A
subset of epiblast cells adjacent to cytotrophoblast
secrete amniotic fluid
16
Q
structure of hypoblast
A
cuboidal cells adjacent to blastocyst cavity
17
Q
what occurs around day 9
A
deeper embedment
transformed blastocyst cavity emerges
18
Q
what is the exocoelomic cavity and its function
A
primitive yolk sac
plays early role in nutrition
later connects to umbilical cord by a yolk stalk
19
Q
primitive yolk sac membrane
A
exocoelomic (Heusers) membrane
formed from hypoblast
20
Q
what occurs around day 12
A
extraembryonic (chorionic) cavity forms; filled with 2 layers of extraembryonic mesoderm
origin: lining of the exocoelomic cavity
21
Q
layers of extraembryonic mesoderm in the chorionic cavity
A
- extraembryonic splanchnopleuric mesoderm: covers yolk sac
2. extraembryoinc somatopleuric mesoderm: lines cytotrophoblast layer
22
Q
what occurs on day 13
A
secondary yolk sac forms within and obliterates the exocoelomic cavity
23
Q
exocoelomic cyst
A
remnants of exocoelomic cavity that are “pinched off”
24
Q
what surrounds the secondary yolk sac
A
lined with extraembryoinc endoderm (from hypoblast)
surrounded by extraembryonic splanchnopleuric mesoderm
25
what lines the amniotic cavity
amnion (inner fetal membrane)
26
what lines the chorionic (extraembryonic) cavity
extraembryoinc somatopleuric mesoderm
27
purpose of gastrulation
goes from a bilaminar to a trilaminar germ disc
| ectoderm, mesoderm, endoderm
28
beginning of gastrulation
primitive streak (furrow on upper surface) forms on epiblast around the tail of the embryo
29
process of invagination in gastrulation
invagination of a subset of epiblast cells
- subset of the invaginated cells displace hypoblast, creating the endoderm (ventral layer)
- subset of invaginating cells lie between epiblast and endoderm/hypoblast creating mesoderm
- epiblast cells remaining form ectoderm (dorsal)
30
how is gastrulation organized
primitive node
| cells in epiblast that form elevated cluster at cranial margin of streak
31
when does gastrulation occur
starts week 3, continues through the end of the 4th week
32
how does the primitive node organize gastrulation
acts as a signaling center to pattern germ layers
33
movement of primitive streak
extends cranially, then regresses caudally
| does NOT move up into head
34
describe the movement of cells in invagination
cells move lateral and cranial, influenced by signaling
- chemo attractive in perimeter
- chemo repulsive at midline
35
why is embryonic disc thickest at midline
this is where ingression is occuring
| mesoderm only exists here before it has the chance to migrate out
36
eventual fate of the hypoblast
replaced by invaginating cells that form the endoderm
| may contribute to lining of primitive yolk sac and extraembryonic endoderm and mesoderm
37
fate of epiblast cells
where epiblast cells migrate through primitive streak determines where cells will end up and what structures they will form
- notochord
- somites
- urogenital system
- body wall
- chorion
38
formation of the notochord overview
prenotochordal cells that ingress through the primitive streak form the notochordal process (a hollow tube)
notochordal process flattens and some cells remain in the mesodermal layer; others intercalate in the hypoblast to form the notochordal plate
39
what 2 cell layers make up the notochord
```
mesodermal
hypoblast (endoderm)
```
40
notochordal plate
cells proliferate and detach from the endoderm (as it replaces the hypoblast) and roll up to form a solid cord of cells
41
establishment of body axes
1. left right
2. dorsal ventral
3. anterior posterior
occurs before and during gastrulation
results in embryonic asymmetry
abnormalities of axes formation results in developmental malformations
42
axis patterning genes in the anterior-posterior axis
AVE (anterior visceral endoderm)- acts with primitive node as a second signaling region in head
-expresses genes essential for head formation and other genes that inhibit formation of the primitive streak in the head
43
when is the cranial end of the embryo established
before gastrulation
44
what maintains the primitive streak (posterior embryo)
nodal
45
ventralization signaling
BMP4 (secreted throughout embryonic disc) ventralizes mesoderm; forms intermediate and lateral plate mesoderm
46
dorsalization signaling
chordin, noggin, and follistatin (secreted by node and prechordal mesoderm) antagonize BMP4 and thus dorsalize cranial mesoderm to form notocord from notochordal plate and paraxial mesoderm
47
dorsal-ventral axis formation at later stage
after notochord is formed - chordin, noggin, and follistatin are expressed by notochord and play a role in neural induction in CRANIAL region
brachyury (T) gene dorsalizes mesoderm in middle and CAUDAL embryo forming paraxial mesoderm
48
where is brachyury (T) gene expressed
node
notochordal precursor cells
notochord
49
goosecoid
dorsalizes cranial/head mesoderm
| activates chordin
50
over/under expression of goosecoid
head malformations similar to conjoined twins phenotype
51
function of brachyury (T) gene
essential for cell migration through primitive streak (mesoderm formation)
AND dorsalizing mesoderm (paraxial mesoderm formation)
52
absence of brachyury (T) gene
decreased formation of mesoderm & decreased PA mesoderm (ie somites)
results in shortening of embryonic axis (caudal dysgenesis) that may result in fusion of the limb buds
53
axis patterning for the left-right axis
gene cascade initiated by FGF8 on the L side establishes expression of nodal on the L
SHH represses L sidedness genes on the R
54
how are cilia related to left-right axis formation
node contains ciliated cells; cilia rotate and set up directional fluid flow (signaling) patterns
55
situs inversus
transposition of viscera in thorax and abdomen
| linked to altered fluid flow
56
when does cephalocaudal differentiation occur
mid 3rd week to mid 4th week
| **gastrulation is still occurring caudally while differentiation is occuring cranially
57
when does the primitive streak stop supplying cells
regresses caudally until the end of the 4th week
58
why does the embryonic disc expand mainly in the cranial region
continuous migration of cells from the primitive streak in the cranial direction
59
association between teratogenesis and gastrulation
in 3rd week, when gastrulation begins, embryo is highly sensitive to teratogenic insult
60
holoprosencephaly
high doses of alcohol (consumed before mother knows she is pregnancy) lead to craniofacial malformations
61
when are holoprosencephaly defects initiated
days 19-21
| when midline of the forebrain is established
62
features of holoprosencephaly
small forebrain
lateral brain ventricles fuse
fusion of lateral nasal prominences
failure of eye fields to separate properly
63
what is a sacrococcygeal teratoma
results from remnants of the primitive streak in the sacrococcygeal region
may contain tissues derived from all 3 germ layers
64
epidemiology of sacrococcygeal teratoma
more often observed in females
| rare: 1 in 37,000
65
mature sacrococcygeal teratoma characteristics
cystic: enclosed in its own fluid containing sac
solid: made up of tissue, but not self enclosed
mixed: containing both solid and cystic parts
typically NOT malignant
66
cardiovascular system at the end of the 3rd week
villus capillaries contact vessels in the chorionic plate and connecting stalk, which in turn contact intraembryonic vessels
67
when is the villous capillary system ready for heartbeat
4th week of development
68
intermediate mesoderm derivatives
kidney
| gonads
69
paraxial mesoderm derivatives
```
head
somite
-sclerotome
-myotome
-dermatome
```
70
lateral mesoderm derivatives
splanchnic (visceral/organs)
somatic (body)
extra-embryonic
71
derivates of the somite
vertebrae and ribs (bones) - sclerotome
dermis of the skin and back - dermatome
skeletal muscles of the back, body wall, and limbs - myotome
72
overview of the urogenital system formation
3 overlapping kidney systems are formed cranial to caudal
- pronephric
- mesonephric
- metanephric
73
cloaca
common embryological cavity
| excretory ducts of both the urinary and genital systems enter here
74
heart formation in weeks 3-4
lateral folding results in cardiac tube formation
75
vasculogenesis
de novo formation of endothelial tubes
76
angiogenesis
sprouting of tubes off existing vessels
77
what are hemangioblasts
common mesodermal precursors for blood cells (hematopoietic cells) and endothelial cells (angioblasts); located in blood islands
78
what cell types are needed for vasculogenesis
both blood cells and endothelial cells
79
what are blood islands
endothelial and blood cell precursors present in the wall of the yolk sac
80
intraembryonic vascular formation
from splanchnic LPM
| occurs slightly after extraembryonic vessel formation (from somatic and splanchnic extraembryonic mesoderm)
81
site changing through the process of hematopoiesis
* *blood cells initially form from splanchnic mesoderm**
1. extraembryonic: blood islands of yolk sac; transitory (week 3)
2. aorta-gonad-mesonephros region
3. liver: colonized by cells from the AGM (2-7 months)
4. bone marrow: colonized by cells from the liver; definitive (7th month of gestation)
82
capillary hemangiomas
occur in 10% of births
may occur anywhere; but often in craniofacial regions
can be focal or diffuse
can disappear without treatment
83
ectodermal derivatives
neural tube
neural crest (epithelial to mesenchymal transformation)
epidermis
sweat glands and hair follicles
84
derivatives of the endodermal germ layer
epithelial lining of: GI tact, respiratory tract, urinary bladder, auditory tube, liver, pancreas, cloaca
85
gut formation from endoderm and cephalocaudal folding
embryonic disc begins to bulge in amniotic cavity as result of brain vesicle growth
folding is most pronounced in head and tail
cephalocaudal folding promotes endoderm lined cavity incorporated into embryo body
86
formation of umbilical cord
portion of the allantois (evagination of hindgut) is surrounded by mesoderm of connecting stalk
together form umbilical cord
blood vessels form from mesoderm
87
foregut
bounded by buccopharyngeal membrane until its rupture in 4th week
88
midgut
temporarily communicates with yolk sac
89
hindgut
terminates temporarily at cloacal membrane until its rupture in 7th week
90
function of lateral folding in formation of the gut tube and ventral body wall
lateral folding results from rapid growth of somites
embryo assumes rounded appearance
gut forms tube and ventral body wall is established
midgut connection with yolk sac becomes long and narrow (vitelline duct)
91
relationship of gut to umbilical cord
at 10 weeks; intestinal loops are herniated into the yolk sac DUCT and are in the umbilical cord due to size constraints of the abdominal cavity
92
defects of the ventral body wall
```
failure to close after lateral folding
ectopia cordis (ectopic heart)
bladder exstrophy
gastroschisis
cloacal exstrophy
```
93
bladder exstrophy
eversion; failure of pelvic region to close
94
gastroschisis
herniation of intestines through abdominal wall
95
cloacal exstrophy
failure of pelvic region to close
96
diagnosis of ventral body wall defects
1. presence of high maternal serum AFP levels (similar to spina bifida)
2. US imaging
97
respiratory development overview
25 days
epithelial lining of larynx, trachea, bronchi, and lungs is endodermal in origin
respiratory diverticulum/lung bud is outgrowth from ventral wall of foregut (4 weeks)
tracheoesophageal septum later divides foregut into: dorsal esophagus, ventral trachea, lung buds
98
what are the pharyngeal arches
5 paired structures surrounding the pharynx
form MSK structures in head and neck
resembles gill formation in fishes and amphibians
99
derivation of pharyngeal arches
derived from paraxial mesoderm (somitomeres and occipital somites) and neural crest cells
covered with ectoderm, lined by endoderm
100
what do the pharyngeal arches contribute to
formation of face, neck, mouth, larynx, pharynx
| muscles, arteries, connective tissue, cartilage, parts of skeleton
101
when does external body form development take place
7-8th week development
limbs have 3 segments
most major organs and organ systems formed
