Lec.7 GASTRULATION Flashcards
As discussed before, ____ leads to the formation of the three germ layers: ecto-, endo- and mesoderm.
This also establishes the germ line, in the form of the ____
gastrulation
primordial germ cells
While gastrulation proceeds, the embryonic disc gradually becomes covered by extra-embryonic membranes to form the ____ cavity
In domestic species, amnion formation results from an ‘upfolding’ of the ____ with its underlying extra- embryonic mesoderm.
amniotic cavity
trophectoderm
During the early phases of gastrulation, the trophectoderm is lined by a thin layer of extra embryonic mesoderm. These two form the ____
this will then forms folds that will surround the embryonic disc.
chorion
The folds extend upwards to meet and fuse above the embryonic disc creating a sealed amniotic cavity.
The term ____ is generally used for the cavity formed and its wall.
Later, this will become surrounded by yet another cavity, the ____
amnion
allantois
The onset of gastrulation is linked to the appearance of the ____
The epiblast cells accumulate posteriorly and thickens in the ____
primitive streak
embryonic disc
*Primitive streak
In the streak, cells start to curl-up from the epiblast to establish ____ these cells give rise to endoderm and mesoderm.
The endoderm-forming cells integrate into, and displace the hypoblast forming the ____
mes-endodermal precursors
endoderm
*Primitive streak
The endoderm enlarges to form the ____ of the primitive yolk sac and is continuous with the hypoblast.
upper lining
*Primitive streak
The endodermally lined portion of the primitive yolk sac will later become enclosed within the embryo proper and develop into the ____
The hypoblast-lined portion of the cavity will be displaced extra embryonically to form the definitive ____
primitive gut
yolk sac
*Primitive streak
The mesoderm each split into two sheets:
One associating with the ____ to form the somatic or parietal mesoderm.
The other associating with the ____ as the visceral or splanchnic mesoderm.
epiblast and trophectoderm
endoderm and hypoblast
*Primitive streak
The cavity forming between the somatic and visceral mesoderm is referred to as the ____
Initially, this is only located outside the embryonic disc and is referred to as the ____
coelom
extra-embryonic coelom or exocoelom.
*Primitive streak
The split between the somatic and visceral mesoderm also involves intra- embryonic mesoderm portions, establishing an ____ coelom which will later give rise to the body cavities
intra-embryonic coelom
*Primitive streak
Growth rate of the embryonic disc overtakes that of the primitive streak, and the disc is lengthened into a ____- shaped structure.
The primitive streak gradually becomes more and more ____ located
pear- shaped
posteriorly
*Primitive streak
Along with the relative posterior withdrawal of the primitive streak, a midline structure, the ____ is formed.
It is formed by epiblast cells entering through the ____
notochord
primitive node
*Ectoderm
In the embryonic disc region anterior to the primitive node, epiblast cells are induced to differentiate into neuroectoderm.
This forms the ____
The edges of the neural plate become elevated, forming the ____
Enclosed is a midline depression known as the ____
neural plate
neural folds
neural groove
*Ectoderm
The neural folds gradually fuse over the neural groove to complete the ____
This process represents the foundation of the first embryonic organ system, which is the ____
neural tube
central nervous system
*Ectoderm
Certain cells at the lateral border or crest of the neural folds become detached.
This cell population, known as the ____, will not participate in formation of the neural tube.
These cells migrate widely and participate in the formation of many other tissues.
neural crest cells
*Ectoderm
Some of the neural crest cells will participate in the formation of the integument (____)
Some, other parts of the nervous system (including neurons for the central, sympathetic and enteric nervous system).
melanocytes
*Ectoderm
Most of the remaining more laterally located epiblast will differentiate into ____
Two bilateral thickenings of the surface ectoderm: the ____ and the _____, will be established in the embryonic cephalic ectoderm.
surface ectoderm
otic placode and lens placode
*Ectoderm
The otic placode invaginates to form the ____, which will develop into the inner ear for hearing and balance.
The lens placode invaginates and forms the ____ of the eye
otic vesicle
lens
*Ectoderm
The remaining surface ectoderm gives rise to the ____ and associated ____ of the skin.
The epithelium covering the oral and nasal cavities will also be formed.
Epithelium covering the oral cavity gives rise to the ____ of the teeth.
epidermis
glands
enamel
*Mesoderm
The mesoderm closest to the notochord (the paraxial mesoderm) proliferates and forms pairs of segmental thickened structures known as ____
These will differentiate further into connective tissue, bone, and cartilage.
somitomeres
*Mesoderm
In the body region, they form ____ from which dermis, skeletal muscle and vertebrae develop.
Formation of somites progresses from the occipital region posteriorly.
somites
*Mesoderm
The ventro-medial part of the somite associates with the notochord establishing the sclerotome which patterns formation of the ____
The dorso-lateral parts become precursors of both dermal and muscle tissue, the ____
vertebral column
dermamyotome
*Mesoderm
The ____ of each somite contributes to muscles of the back and limbs
The ____ disperses and forms the dermis and subcutis of the skin.
Each myotome and dermatome will receive its own segmental nerve component (innervation).
myotome
dermatome
*Mesoderm
The ____ connects the paraxial and lateral plate mesoderm.
It differentiates into structures of both the urinary system and the gonads (urogenital system).
intermediate mesoderm
*Mesoderm
The intermediate mesoderm in the cervical and cranial thoracic regions forms ____
Caudally the nephrogenic cord is formed, that will be a temporary kidney, the ____
In the medial aspect, the gonads start to form in order to receive the PGCs.
nephrotomeres
mesonephros
*Mesoderm
The ____ will provide all other components of the gut (that are not derived from endoderm) and its derivatives.
Both blood and blood vessels appear to arise from the ____
These differentiate into ____ stem cells (forming blood cells) and ____ (forming blood vessels).
visceral mesoderm
hemangioblasts
hematopoietic stem cells
angioblasts
*Endoderm
The inner epithelial lining of the gastrointestinal tract and its derivatives are derived from the ____
The endoderm-enclosed portion of the primitive yolk sac is enclosed within the embryo forming the ____, whereas the hypoblast-enclosed portion becomes localized outside the embryo to form the definitive ____
endoderm
primitive gut
yolk sac
*Endoderm
The primitive gut comprises cranial (foregut), middle (midgut) and caudal (hindgut) parts.
Endoderm of the foregut gives rise to: (6)
pharynx
middle ear
esophagus
stomach
liver
pancreas
*Endoderm
The ____ gives rise to most of the small and the large intestine down to the transverse colon.
This also connects with the yolk sac through the ____
The ____ gives rise to the transverse and descending colon as well as the rectum and part of the anal canal.
midgut
vitelline duct
hindgut
*Endoderm
During the ____ week of development, the allantois is formed as an outgrowth from the hindgut into the extraembryonic coelom.
The allantoic duct along with the vitelline duct becomes incorporated into the ____
second or third week
umbilical cord
*Primordial germ cell
During formation of the mesoderm and endoderm, a certain population of epiblast cells is set aside for formation of the future ____
As the somatic germ layers form, the primordial germ cells are displaced from the embryonic disc area to the wall of the definitive yolk sac and, to some degree, of the allantois.
germ line
The PGCs multiply in the yolk sac wall and then relocate into the ____
The PGCs continue to multiply for a while until they either initiate meiosis (female embryo) or enter mitotic arrest until puberty (male embryo).
This ends the gastrulation stage.
developing gonads
