Weeks 2 & 3 Development Flashcards
describe week 2
- implantation completed
- trophoblast differentiates into 2 layers
- embryoblast forms 2 layers
- extraembryonic mesoderm splits into 2 layers
- 2 cavities form
day 8- trophoblast differentiated
- cytotrophoblast
- syncytiotrophoblast
day 8- embryoblast differentiates:
- hypoblast
- epiblast
day 8, the _____ forms
amniotic cavity
amnioblasts are…
epiblast cells adjacent to cytotrophoblast
During day 9, ____ migrate peripherally forming the _____
hypoblast cells; exocoelomic (heuser) membrane
the exocoelmic membrane and the hypoblast forms lining of _____
exocoelmic cavity (also called primitive yolk sac or primary umbilical vesicle)
During day 9, _____ fills in tiny space in _____
fibrin coagulum; endometrial wall
During day 9, _____ appear in syncytium of _____
vacuoles; embryonic pole
during day 9, fuse form _____ called the _____
lacunae; lacunar stage
During days 11 and 12…
- trophoblast characterized by lacunar spaces in the syncytium; forms intercommunicating network
- Cells of syncytiotrophoblast erode endothelial lining of maternal capillaries; sinusoids
- syncytial lacunae become continuous with sinusoids
- establishes uteroplacental circulation
during days 11 and 12, blastocyst is completely _____
embedded in stroma
During days 11 and 12, new cells appear between inner surface of ____ and outer surface of _____, forming the _____
cytotrophoblast; exocoelomic cavity; extraembryonic mesoderm
days 11 and 12 the cells lining the primary umbilical vesicle form a layer of _____ that surrounds the _____ and ______
extraembryonic mesoderm; amniotic cavity; primary umbilical vesicle (yolk sac)
days 11 and 12, large cavities known as the _____ form in _____ and will eventually fuse
extraembryonic coelomic spaces; extraembryonic mesoderm
days 11 and 12…
- large cavities form in extraembryonic mesoderm
- form extraembryonic cavity (aka chorionic cavity)
- chorionic cavity surrounds amnion and umbilical vesicle except at connecting stalk
the extraembryonic mesoderm lining cytotrophoblast and amnion is _____
extraembryonic somatic mesoderm
the extraembryonic mesoderm covering the yolk sac
extraembryonic splanchnic mesoderm
day 13
- trophoblast characterized by primary villi
- hypoblast produces cells that form secondary yolk sac (aka definitive yolk sac); exocoelomic cysts in the extraembryonic coelom (chorionic cavity)
during day 13, the _____ forms
chorionic cavity
extraembryonic mesoderm lining inside of cytotrophoblast
chorionic place
_____ will develop into the umbilical cord with development of blood vessels
connecting stalk
chorionic cavity surrounds ____ and _____ except at _____
amnion; umbilical vesicle; connecting stalk
at the end of week 2, a thickening develops in a region of the ____ where the cells become _____ in shape (this is known as the _____)
hypoblast; columnar; prechordal plate
the prechordal plate indicates the future site of the ____
mouth
recap of week 2
- implantation completed
- uteroplacental circulation established
- embryoblast develops into bilaminar disc
- amniotic and chorionic cavities form
- extraembryonic mesoderm forms
- primary and secondary yolk sacs form
week 3
- formative of primitive streak and node
- gastrulation occurs
- formation of notochord
- establishment of body axes
- growth of the embryo
formative process by which the 3 embryonic germ layers are formed
endoderm, mesoderm, ectoderm all formed by gastrulation
endoderm, mesoderm, ectoderm all formed from _____
epiblast
gastrulation begins with formation of ______
primitive streak
cephalic end of primitive streak =
primitive node which surrounds the primitive pit
during gastrulation, epiblast cells migrate towards _____ and slip beneath epiblast, which is called _____
primitive streak; invagination
invaginating epiblast cells:
- displace/replace hypoblast cells forming endoderm
- lie between epiblast and endoderm to form mesoderm
- cells remaining in epiblast form ectoderm
hypoblast cells are fairly ___ and not ___; the migrating epiblast cells which displace/replace the hypoblast cells are much more ___ and ____; the same goes for the epiblast cells which remain in the epiblast and do not migrate; they will also become more ____ to form the ____
thin; robust; robust; substantial; robust; ectoderm
during gastrulation, cells continue to spread ____ and _____; in cephalic direction, pass on each side of _____
laterally; cranially; prechordal plate
the prechoral plate is formed between the tip of the ____ and ____
notochord; oropharyngeal membrane (future opening of the oral cavity)
during notochord formation, _____ invaginate in the _____ which forms the _____
prenotochordal cells; primitive pit; notochordal process
the notochordal process grows cranially from the _____ until it reaches the _____ and acquires a ____, which is known as the ____
primitive node; prechordal plate; lumen; notochordal canal
the floor of the _____ fuses with ____ below and it degenerates
notochordal process; endoderm
once the floor degenerates, the _____ now has open connection with _____ through what is known as the _____
amniotic cavity; umbilical vesicle; neurenteric canal
two other names for extracoelomic cavity
primitive yolk sac and primary umbilical vesicle
the notochordal process is basically a hollow tube of _____ which move forward _____ from ____ to _____
prenotochordal cells; cranially; primitive node; prechordal plate
remains of notochordal process comprise the _____; this ____ separates from _____, folding in to form the ____
notochordal plate; notochordal plate; endoderm; notochord
recap of notochord formation
The ventral floor of the tube fuses with the underlying endoderm and the two layers breakdown, leaving the flattened notochordal plate. (At the level of the primitive pit the yolk sac is transiently communicating with the amniotic cavity thru the neurenteric canal).
The notochordal plate then detaches from the endoderm, into the mesoderm containing space between the endoderm and ectoderm, forming a solid rod = notochord.
the cloacal membrane is formed at the _____ of the _____
caudal end; embryonic disc
cloacal membrane similar to ______
oropharyngeal membrane
yolk sac forms _____ that extends into ______; allantois forms around _____
diverticulum; connecting stalk; day 16
allantois in lower vertebrates serves as a reservoir for ____ products of the _____; in humans, it remains ____ but may be involved in abnormalities of _____
excretion; renal system; rudimentary; bladder development
beginning of week 3, trophoblast is characterized by _____; _____ covered by _____
primary villi; cytotrophoblastic core; syncytial layer
further development of trophoblast: _____ penetrate core of primary villi (secondary villus)
mesodermal cells
end of 3rd week, mesodermal cells differentiate into ____ and _____
blood cells; small blood vessels (tertiary villus)
capillaries in tertiary villi make contact with capillaries developing in _____ of _____ and in ______; contact established with ______, connecting the ____ and ____
mesoderm; chorionic plate; connecting stalk; intraembryonic circulatory system; placenta; embryo
blood vessels arise from blood islands
vasculogenesis
blood vessels sprouting from existing vessels
angiogenesis
____ cavity enlarges; embryo attached to its _____ by narrow _____
chorionic; trophoblastic shell; connecting stalk
connecting stalk will develop into the _____ with development of _____
umbilical cord; blood vessels
recap of week 3
- formation of primitive streak and node
- gastrulation occurs
- formation of notochord
- establishment of body axes
- growth of the embryo
- primary to secondary to tertiary villi
