Lecture 4 - Early Embryogenesis Flashcards
when does cleavage of the zygote happen
mitotic division happens rapidly at 30 hours after fertilization
What day?
12 -32 blastomeres (=morula)
inner cell mass (embryoblast) surrounded by layer of flattened cells (trophoblast)
Day 3
trophoblast secretes
early pregnancy factor
What day?
morula is now called blastocyst
blastocystic cavity forms
Day 4
outer cells that give rise to the embryonic part of the placenta
trophoblast
cells that form the embryo
embryoblast
What day?
blastocyst travels in uterine fluid and sheds zona pellucida
Day 5-6
what day?
blastocyst attaches to endometrial lining
trophoblast differentiates into two layers
Day 6
trophoblast differentiates into (2)
cytotrophoblast - inner layer of cells
synctiotrophoblast - outer layer of cells that extends into endometrial epithelium and allows the blastocyst to “burrow” in
synctiotrophoblast secretes
Human chorionic gonadotropin (hCG)
What happens in week 2? (4 things)
blastocyst implants
formation of embryonic disc
formation of amniotic cavity
trophoblast continues to differentiate
week 2: embryoblast forms embryonic disc, which consists of (2)
epiblast - thicker layer that forms floor by amniotic cavity
hypoblast - thinner layer, continuous with the primordial umbilical vesicle
what is the exocoelemic membrane?
forms to make the primary umbilical vesicle and surrounds the blastocystic cavity
________ cavity is on top of developing embryo and
________ cavity is below
amniotic
blastocystic
what is the amnion
thin, transparent, nonvascular cavity
formed by aminogenic cells, maternal blood, and fetal kidneys
functions of amnion (3)
protective cushion
temperature
free movement
what day?
embryo completely embedded in endometrium
closing plug forms
endometrial wall regenerates, covering the plug
Day 10
what is the chorion?
the outermost membrane surrounding the embryo
what do the chorionic villi do?
extract nutrients from maternal blood and endometrial tissue
when do primary chorionic villi appear?
end of week 2
What happens in week 3? (3 general things)
gastrulation - differentiation of 3 germ layers
development of notochord
Allantois and chorionic villi formation
Define:
primitive streak
primitive groove
primitive node
primitive pit
streak - cells migrate to dorsal caudal location and elongate by adding more cells
groove - small depression in primitive streak
node - cluster of cells at cranial end of primitive streak
pit - deepest part of primitive groove
cells leave the primitive streak to form _____
mesenchyme
what is a sacrococcygeal teratoma
remnants of primitive streak persist
- tumor has tissues from all 3 germ layers at different points of formation
Inductions for gastrulation
growth factors and signaling from cells, coordinate factors with genes, cell interactions, proliferation of cells, and apoptosis
where does notochordal process begin to form?
deep to the primitive pit
notochordal process (with notochordal canal) extends cranially to _______ ________
prechordal plate
cellular rod formed from axial mesoderm that creates the axis of the embryo, is a template for development of bones of the head and vertebral column, is site of vertebral bodies, and forms the neural plate
notochord
define neural plate (general)
primordial CNS
notochord degenerates and forms the _____
nucleus pulposus of IV discs
describe development of neural tube (day 18)
central axis of neural plate invaginates and forms the neural GROOVE with neural FOLDS.
The FOLDS then fuse together to form the the neural TUBE which separates from the ectoderm
what do neural crest cells do
separate from the neural tube as it’s developing, and begin to lay framework for PNS
name 2 neural tube defects
spina bifida
anencephaly
what are somites
surface elevations in paraxial mesoderm
form axial skeleton, muscle, and some skin
transcription factors involved in the development of somites (2)
Fox C1 and C2
Delta-Notch
The allantois develops from the ________ and is the basis of ___________ and __________
umbilical vesicle
early blood formation
urinary bladder
main exchange site of material between embryo and maternal blood
chorionic villi
brings primordium of brain above heart and oropharyngeal membrane
head fold
brings tail region over cloacal membrane, umbilical cord is brought ventrally
tail fold
brings edges of embryonic disc ventrally forming a cylindrical embryo
lateral fold
________ is brought ventrally and fuses with _______ to form umbilical cord
connecting stalk
umbilical vesicle
when does folding happen? (week)
Week 4
what appears in week 4? (6)
pharyngeal arches upper limb buds lower limb buds otic pits - future internal ears lens placodes - future lenses rudimentary cardiovascular system
Highlights of week 5 (2)
Growth of head rapidly increases
mesophrenic ridges - future kidneys
Highlights of week 6 (3)
twitching
digital rays - digits
auricular hillocks - auricle of ear
Highlights of week 7 (1)
Hand plates - notches separate future digits
Highlights of week 8 (6)
digits separated, but webbed
eyelids close
hands and feet grow towards each other ventrally
head is disproportionately large
primary ossification centers begin to form
sex differences begin
