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
