Embryonic Development Gastrulation

Question 1

Gastrulation begins with…

Answer 1

The formation of the bilaminar embryo

Question 2

How does the embryonic disc/bilaminar embryo form?

Answer 2

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

Question 3

What 2 layers is the embryonic disc made up of?

Answer 3

Epiblast- top layer
Hypoblast- second layer; extends towards the trophoblast cells and goes under it

Question 4

Intra-embryonic is what occurs at the level of…
Extra-embryonic is what occurs at the level of…

Answer 4

At the level of the embryonic disc
At the level of the trophoblast cells and hypoblast cells that have extended below it

Question 5

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?

Answer 5

The yolk sac

Question 6

The hypoblast under the trophectoderm cells is called…

Answer 6

The extra-embryonic endoderm

Question 7

Once the bilaminar embryonic disc has formed, what forms next?

Answer 7

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

Question 8

How does the primitive streak form?

Answer 8

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

Question 9

In primitive streak, the epiblast cells form into what cell?

Answer 9

The mesoderm cells

Question 10

What do the mesoderm cells do once they have formed from the epiblast cells?

Answer 10

1.Populate the whole embryonic disc
2. Move under the trophoblast cells in the yolk sac forming the extra-embryonic mesoderm

Question 11

Name the components of the embryo shown here

Answer 11

On anki

Question 12

What is the primitive/midline groove

Answer 12

two epiblast ridges with a depression in between, into which epiblast cells move to transform into the mesoderm cells

Question 13

The whole embryonic disc will be covered in mesoderm cells, except for what structures?

Answer 13

Buccopharyngeal membrane (cranial ‘mouth’)
Cloacal membrane (caudal ‘anus’)

Question 14

What is the Hensen’s node and what is its function?

Answer 14

primitive knot or primitive node formed at cranial end of primitive streak
-responsible for formation of the notochord and mesoderm of the head

Question 15

What is the notochord? What is it responsible for?

Answer 15

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

Question 16

What happens once the mesoderm formation is complete?

Answer 16

the primitive streak shrinks in relation to the rapidly elongating disc

Question 17

What are monozygotic twins?

Answer 17

Genetically identical twins

Question 18

How do monozygotic twins arise?

Answer 18

Arise due to formation of two primitive streaks on a single embryonic disc

Question 19

In monozygotic twins, incomplete separation of the two primitive streaks on a single embryonic disc will lead to…

Answer 19

Conjoined twins

Question 20

Name the 3 germ layers of the embryo

Answer 20

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)

Question 21

What type of tissue will each germ layer of embryo become in the adult body?

Answer 21

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)

Question 22

What are the 3 different derivatives/sections of the intra-embryonic mesoderm?

Answer 22

The Paraxial (next to notochord) mesoderm
The Intermediate mesoderm
The Lateral mesoderm

Question 23

The paraxial mesoderm
-situated where
-forms what

Answer 23

Situated right next to the notochord
Forms the somites typical for early embryos

Question 24

Intermediate Mesoderm
-forms where & borders what
-forms what?

Answer 24

-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

Question 25

Lateral mesoderm Made of what 2 layers?

Answer 25

Made of 2 layers; somatic and splanchnic layers Somatic—> lies under (troph)ectoderm Splanchnic—> surrounds endoderm

Question 26

Somites -what are they -precursors to what

Answer 26

-Repeating segments derived from the mesoderm, paired blocks on either side of notochord -precursors to many structures in the body like the skeleton

Question 27

What 3 regions will the somites differentiate into

Answer 27

dermatome (subcutis), myotome (muscles, ligaments) sclerotome (vertebra, bones)

Question 28

What can number of somites present allow a vet to do?

Answer 28

Age an embryo

Question 29

Fluid filled space between the intra & extra-embryonic layers is called?

Answer 29

Coelom

Question 30

What is the septum transversum?

Answer 30

structure that forms during embryonic development and plays an important role in the formation of the diaphragm

Question 31

What are the 3 main body cavities formed by the. Intra-embryonic coelom?

Answer 31

the pericardial cavity, which surrounds the heart; the pleural cavity, which surrounds the lungs; and the peritoneal cavity, which surrounds the abdominal organs.

Question 32

Now that disc-shaped trilaminar embryo is formed, what does it undergo?

Answer 32

Tubulation

Question 33

In tubulation, the outer and inner tubes formed are from what?

Answer 33

Outer—> ectoderm layer of embryo Inner—> digestive tube

Question 34

What is the neutral plate?

Answer 34

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

Question 35

What is neurulation? What is the neural tube?

Answer 35

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

Question 36

Describe the steps of primary neurulation

Answer 36

-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

Question 37

Neural crest cells -considered… -formed from what -form structures of the…

Answer 37

-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

Question 38

Finally, embryo undergoes final stage of formation called…

Answer 38

Flexion—> folding into a sort of C-shape

Question 39

The typical body form of the embryo is a

Answer 39

C-shape

Question 40

When does gastrulation start, before or after hatching of the blastocyst?

Answer 40

After hatching

Question 41

What term is given to the area in the bilaminar embryo which will form the proper embryo?

Answer 41

Embryonic disc

Question 42

What is the function of the primitive streak

Answer 42

Formation of mesoderm

Question 43

Caudal on the embryonic disc, what is the term given to the area where the embryo remains bilaminar?

Answer 43

Cloacal membrane

Question 44

What germ layer do the body cavities derive from?

Answer 44

Lateral mesoderm

Question 45

During embryo development which embryonic organ changes position and allows the determination of the head and the tail in the C-shape?

Answer 45

The heart