Embryonic Development Gastrulation Flashcards
Gastrulation begins with…
The formation of the bilaminar embryo
How does the embryonic disc/bilaminar embryo form?
Forms when the outer trophoblast cels covering ICM cells degenerate allowing the inner cell mass (ICM) cells to proliferate and move to surface of the embryo forming a flat disc
What 2 layers is the embryonic disc made up of?
Epiblast- top layer
Hypoblast- second layer; extends towards the trophoblast cells and goes under it
Intra-embryonic is what occurs at the level of…
Extra-embryonic is what occurs at the level of…
At the level of the embryonic disc
At the level of the trophoblast cells and hypoblast cells that have extended below it
The formation of the embryo disc causes the layers to grow. The hypoblast continues under the
trophectoderm cells forming a continuous sheet lining the interior of the blastocyst. What does this form inside?
The yolk sac
The hypoblast under the trophectoderm cells is called…
The extra-embryonic endoderm
Once the bilaminar embryonic disc has formed, what forms next?
The primitive streak—> a linear band of thickened epiblast that first appears at the caudal end of the embryo and grows cranially
This means the embryonic disc is now trilaminar
How does the primitive streak form?
Epiblast cells of embryonic disc begin to proliferate, move and thicken long the embryonic disc diameter. Move into primitive groove, underneath epiblast, above hypoblast and transdifferentiate into different cell type called mesoderm cells
In primitive streak, the epiblast cells form into what cell?
The mesoderm cells
What do the mesoderm cells do once they have formed from the epiblast cells?
1.Populate the whole embryonic disc
2. Move under the trophoblast cells in the yolk sac forming the extra-embryonic mesoderm
Name the components of the embryo shown here
On anki
What is the primitive/midline groove
two epiblast ridges with a depression in between, into which epiblast cells move to transform into the mesoderm cells
The whole embryonic disc will be covered in mesoderm cells, except for what structures?
Buccopharyngeal membrane (cranial ‘mouth’)
Cloacal membrane (caudal ‘anus’)
What is the Hensen’s node and what is its function?
primitive knot or primitive node formed at cranial end of primitive streak
-responsible for formation of the notochord and mesoderm of the head
What is the notochord? What is it responsible for?
A solid rod of mesoderm cells which expands cranially from the primitive node and will form the mesoderm of the head & development of neuronal-ectoderm above notochord
What happens once the mesoderm formation is complete?
the primitive streak shrinks in relation to the rapidly elongating disc
What are monozygotic twins?
Genetically identical twins
How do monozygotic twins arise?
Arise due to formation of two primitive streaks on a single embryonic disc
In monozygotic twins, incomplete separation of the two primitive streaks on a single embryonic disc will lead to…
Conjoined twins
Name the 3 germ layers of the embryo
Ectoderm (single cell outer layer, used to be epiblast)
Mesoderm (multiple, loosely arranged cell layers in the middle)
Endoderm (single cell inner layer, used to be hypoblast)
What type of tissue will each germ layer of embryo become in the adult body?
Ectoderm—> epithelial surface (skin) and neural tissue
Mesoderm—> muscle, bone, blood, connective tissue, gonads, kidneys
Endoderm—> gut lining, associated structures (eg. liver, trachea and lungs)
What are the 3 different derivatives/sections of the intra-embryonic mesoderm?
The Paraxial (next to notochord) mesoderm
The Intermediate mesoderm
The Lateral mesoderm
The paraxial mesoderm
-situated where
-forms what
Situated right next to the notochord
Forms the somites typical for early embryos
Intermediate Mesoderm
-forms where & borders what
-forms what?
-Forms lateral to the somites and borders the intra-embryonic coelomic space
-Will become the urogenital system; forms the;
Embryonic kidneys
‘Adult’ final kidneys
Urinary duct system
Gonads and reproductive duct system
Lateral mesoderm
Made of what 2 layers?
Made of 2 layers; somatic and splanchnic layers
Somatic—> lies under (troph)ectoderm
Splanchnic—> surrounds endoderm
Somites
-what are they
-precursors to what
-Repeating segments derived from the mesoderm, paired blocks on either side of notochord
-precursors to many structures in the body like the skeleton
What 3 regions will the somites differentiate into
dermatome (subcutis),
myotome (muscles, ligaments)
sclerotome (vertebra, bones)
What can number of somites present allow a vet to do?
Age an embryo
Fluid filled space between the intra & extra-embryonic layers is called?
Coelom
What is the septum transversum?
structure that forms during embryonic development and plays an important role in the formation of the diaphragm
What are the 3 main body cavities formed by the. Intra-embryonic coelom?
the pericardial cavity, which surrounds the heart;
the pleural cavity, which surrounds the lungs;
and the peritoneal cavity, which surrounds the abdominal organs.
Now that disc-shaped trilaminar embryo is formed, what does it undergo?
Tubulation
In tubulation, the outer and inner tubes formed are from what?
Outer—> ectoderm layer of embryo
Inner—> digestive tube
What is the neutral plate?
structure that forms during the early stages of embryonic development
-flat, elongated sheet of ectodermal cells that develop in the ectoderm and are found above the notochord
What is neurulation?
What is the neural tube?
Process by which the neural tube forms during embryonic development
The neural tube is a structure that eventually gives rise to the brain and spinal cord
Describe the steps of primary neurulation
-Edges of the neural plate start to fold
-as they continue to fold inwards, the plate begins to close over
-plate eventually completely closes resulting in the formation of the neural tube
Neural crest cells
-considered…
-formed from what
-form structures of the…
-Considered 4th germ layer
-formed from the edges of the neural plate as it folds
-populate/form structures of the;
Head
Heart CT
Parasympathetic and sympathetic ganglia
Finally, embryo undergoes final stage of formation called…
Flexion—> folding into a sort of C-shape
The typical body form of the embryo is a
C-shape
When does gastrulation start, before or after hatching of the blastocyst?
After hatching
What term is given to the area in the bilaminar embryo which will form the proper embryo?
Embryonic disc
What is the function of the primitive streak
Formation of mesoderm
Caudal on the embryonic disc, what is the term given to the area where the embryo remains bilaminar?
Cloacal membrane
What germ layer do the body cavities derive from?
Lateral mesoderm
During embryo development which embryonic organ changes position and allows the determination of the head and the tail in the C-shape?
The heart
