embryo 2 (wk8) Flashcards
what axis does the notochord develop
longitudinal axisw
what structure does notochord contribute to
intervertebral discs
what does the notochord provide signals for
Providessignalsfor the development of axial MSK structures and the CNS
how is the notochordal process formed
mesenchymal cells dive
into the primitive pit and migrate cephalad
what is the lumen in the notochordal process called
Notochordal canal
how does the notochordal process become the notochordal plate
notochordal process approaches the prechordal plate, the floor of the process “fuses” with the endoderm
how can the amniotic cavity and umbilical vesicle communicate through
an opening (the neurenteric canal)
– this opening is where the primitive pit opened into the notochordal canal
what happens to the notochordal plate to form the notochord
cells proliferate and fold inwards
-no canal present
▪ Notochordal plate! notochord transition starts cranially (cephally) and progresses caudally
- After the notochord is fully-developed, the neurenteric canal is obliterated
what layer is absent in the floor of the plate where the neurocentric canal is
endoderm
what do the notochord and its preceding structures (process, plate) help organize?
-induce overlying ectoderm to develop into neural plate
-acts as central axis (divide left and right)
what thing does the notochord structures approach but not go beyond
the prechordal plate
what does the prechrodal plate organzie
cranial structures
what does the prechordal plate act as a stop signal for
notochord; prevent it from going to far anteriorly
what does the prechordal plate develop into
the oropharyngeal membrane
oropharyngeal membrane; how many layers and where is it found
2 layers; ecto and endoderm
cardiogenic mesoderm found anteriroly
where does the cloacal membrane form
caudal to the primitive streak
how many layers in cloacal membrane and what does it become
2; ecto and endoderm
future site of anus
what is the allantois
Small, vascularized diverticulum (outpouching) from the caudal wall of umbilical vesicle, extending into connecting stalk
what does the allantois function in
early blood formation and bladder development
▪ Blood vessels become umbilical arteries
▪ Small portion persists as urachus that extends from bladder to umbilical region
- Becomes median umbilical ligament in adults
how does neuroectoderm form
Notochord induces overlying ectoderm to form the neural plate
what does neuroectoderm give rise to
Gives rise to the CNS, retina, and the tissues that arise
from the neural crest
on day 18, what does neural plate invagination cause formation of
On day 18, the neural plate invaginates to form the neural groove – neural folds are found on either side of the groove
how is neural tube made
The neural folds eventually fuse together, and form the neural tube
what is the structure the neural tube makes
is the primordium of the CNS
when is neuralation complete
end of week 4
derivative of neural crest cells…
▪ Ganglia of CN V, VII, IX, X
▪ Spinal ganglia (i.e. dorsal root
ganglia)
▪ Autonomic nervous system ganglia
▪ Neurolemma sheaths of peripheral nerves
▪ Contribute to the arachnoid and pia
▪ Adrenal medulla
▪ Melanocytes
▪ Craniofacial bone and cartilage
▪ Portions of the heart
what are the 3 structures that the intraembryonic mesoderm proliferates to from a thick column of mesoderm on the sides of the notochord
During the 3rd week:
▪ Intraembryonic mesoderm proliferates to form a thick
column of mesoderm on either side of the notochord
* Beside the axis of the organism (as defined by the
notochord) = paraxial mesoderm
▪ The intermediate mesoderm is found just lateral to the
paraxial mesoderm
▪ The lateral mesoderm is lateral to the intermediate mesoderm
what are somites
During the 3rd – 5th week, somites develop adjacent to the neural tube
- Somite = cuboidal masses of mesoderm on either side of the notochord, visible along the dorso-lateral surface of the embryo on each side of the neural tube
what are the somites formed from
- Formed from the paraxial mesoderm
what do somites give rise to
Somites give rise to most of the axial skeleton and associated musculature, as well as the dermis in those areas
how is primordial heart formed
- During the 3rd week mesenchymal cells migrate anteriorly, lateral to the notochordal process to eventually form cardiogenic mesoderm
▪ Found anterior to the prechordal plate, eventually gives rise to the embryonic heart primordia
▪ The heart begins as a pair of tubes that are brought together by folding of the embryo
intraembrionic coelom is found in?
appears as isolated spaces in the lateral mesoderm and cardiogenic mesoderm
▪ These spaces soon coalesce (join together) and form a single horseshoe-shaped intraembryonic coelom
which 2 layers does the intra-embryonic coelom divide the lateral mesoderm into
▪ A somatic or parietal layer of lateral mesoderm located beneath the ectodermal epithelium and continuous with the extraembryonic mesoderm covering the amnion
▪ of lateral mesoderm next to the endoderm and continuA splanchnic or visceral layer ous with the extraembryonic mesoderm covering the umbilical vesicle
3 regions that are in the lateral mesoderm on day 19-21that come from the intraembryonic coelom
Somatopleure – the somatic mesoderm and the overlying ectoderm
* Forms the body wall
▪ Splanchnopleure – the splanchnic mesoderm and the underlying intraembryonic endoderm
* Forms the embryonic gut
▪ Intraembryonic coelom in between the somatopleure and splanchnopleure
what does the somatopleure form?
body wall
what does the splanchnopleure form?
embryonic gut
where in the intraembryonic coelom
in between the somatopleure and splanchnopleure
during the 2nd month what does the intraemnyronic coelom develop into? hint 3 cavities
▪ Pericardial cavity
▪ Pleural cavity
▪ Peritoneal cavity
2 types of folding
median plane= cranial-caudal folding
–> brain vesicles and somites
horizontal plane= lateral folding
–> body wall
stomodeum
primordial of the mouth
foregut
Part of the endoderm of the umbilical vesicle is incorporated into the embryo as the foregut
▪ The foregut lies between the brain and heart
▪ Oropharyngeal membrane separates the foregut from the stomodeum
septum transversum
Septum transversum lies caudal to the heart
▪ develops into the central tendon of the diaphragm and separates the abdominal cavity from the thoracic cavity
tail folding
caudal eminence (tail region) projects over the cloacal membrane (future site of anus)
Part of the endodermal germ layer is incorporated into the embryo as the hindgut
connecting stalk (primordium of umbilical cord)
which folding makes foregut, hindgut and midgut
cranial folding= foregut
lateral folding= midgut
tail folding= hindgut
what does lateral folding make
mid gut
omphaloenteric duct (decrease connection between midgut and umbilical vesicle)
when does neural plate begin
day 19
when does neurulation end
day 27
what happens to end neuraltion
closure of neuropores
at this point the neural tube no longer communicates with the amniotic cavity
when neuropore close what happens to circulation
After neuropore closure, a basic blood circulation has been established
what makes the brain and spine
- At day 22, the cranial 2/3 of the neural tube forms the brain, caudal 1/3 of the neural tube will form the spinal cord
what are the 3 zones that are in the spinal cord and which one is developed first
ventricular zone (inner) - developed 1st
intermediate zone
outer marginal zone
what do the 3 zones of the spinal cord become
ventricular zone (inner) - neurons and microglia
intermediate zone- primordial neuroblasts
outer marginal zone- white matter tracts
what cells line the central canal of the spinal cord
ependymal cells
what are the 3 primary brain vesicles
forebrain (prosencephalon)
midbrain (mesencephalon)
hindbrain (rhombenceophalon)
what does the forebrain (prosencephalon) divide into during week 5
telencephalon and diencephalon
what does the hindbrain (rhombenceophalon) divide into during week 5
metencephalon and myencephalon
on day 25 what forms on the forebrain
2 lateral outgrowuth- optic vesicles
what do the 2 lateral outgrowths on the forebrain turn into
primordia of the retinae and optic nerves
what are the telencephalon vesicles the primordial of
cereberal hemisphere and lateral ventricles
what do the three swellings of the third ventricle become
thalamus, hypothalamus and epithalamus
what are the alar plate of the spinal cord
dorsal gray horns
what are the basal plates of the spinal cord
ventral and lateral gray horns
