Lecture 8 - Gastrulation and Germ Layers

Question 1

process towards gastrulation

Answer 1

cleavage -> blastula -> gastrula

Question 2

meaning of gastrla

Answer 2

Greek word “gaster” meaning stomach

Question 3

• characterized by profound well-ordered rearrangements of the cell in the embryo
• major changes is the acquisition by the cells of the capacity for undergoing morphogenetic movements which often result in the reorganization of the entire embryo

Answer 3

Gastrulation

Question 4

Major morphogenetic movements

Answer 4

1. invagination
2. evagination
3. involution
4. epiboly
5. ingression
6. delamination (poly-ingression)
7. amoeboid motion

Question 5

infolding of cell sheet into embryo

Answer 5

invagination

Question 6

refers to the outward bulging or protrusion of an epithelial sheet, forming an outpouching

Answer 6

evagination

Question 7

inturning of cell sheet over the basal surface of an outer layer

Answer 7

involution

Question 8

migration of individual cells into the embryo

Answer 8

ingression

Question 9

splitting or migration of one sheet into two sheets

Answer 9

delamination

Question 10

expansion of one cell sheet over other cells

Answer 10

epiboly

Question 11

cells move by extending temporary, finger-like protrusions called pseudopodia, driven by cytoplasmic streaming and cytoskeletal rearrangements.

Answer 11

amoebid motion

Question 12

two main strategies to handle gastrulation

Answer 12

1. within the context of a sphere
2. dictated by the amount of yolk found in large eggs

Question 13

gastrulation movement in amphioxus

Answer 13

in-pocketing (invagination)

Question 14

cavity in gastrulation

Answer 14

archenteron / gastrocoel

Question 15

opening from the outside into the archenteron

Answer 15

blastopore

Question 16

three germ layers

Answer 16

1. ectoderm
2. endoderm
3. mesoderm

Question 17

when does morphogenetic movements begin in gastrulation of sea urchin embryos

Answer 17

late blastula stage with separation of primary mesenchyme from the wall (vegetal plate) of the blastula

Question 18

gastrulation in sea urchin embryos

Answer 18

1. primary mesenchymal cells
2. develop projections
3. filopodia
4. move along the basal lamina that lines the blastocoel
5. form a loose ring-like structure near the base of the invaginating archenteron

Question 19

main feature of gastrulation in sea urchin

Answer 19

formation of archenteron or primitive gut

Question 20

gastrulation in three stages

Answer 20

1. inpocketing or invagination of cells at the vegetal pole and their elongation into blastocoel
2. presence of secondary mesenchymal cells which become indistinguishable at the innermost tip of the archenteron
3. tip of the archenteron makes contact with the blastocoel wall

Question 21

follows ingression of mesenchyme

Answer 21

invagination of endoderm

Question 22

Four destined types of cells after contact with the wall of blastocoel

Answer 22

1. pigment cells
2. blastocoelar cells
3. two coelomic pouches which protrude from the tip of archenteron
4. circumesophageal musculature

Question 23

what happens after the archenteron reaches the opposite wall of the blastula

Answer 23

resulting bilaminar layer soon ruptures to form the oral opening

Question 24

what happens to the blastopore

Answer 24

becomes the anus

Question 25

cortical rotation in amphibian embryo stimulated by sperm fusion leads to generation of what

Answer 25

Nieuwkoop center, early organizing center, in dorsal cells

Question 26

where does gastrulation begin in amphibians

Answer 26

dorsal blastopore lip

Question 27

final movements of epiboly

Answer 27

1. encase the embryo in ectoderm
2. internalize the endoderm

Question 28

process of gastrulation

Answer 28

1. surface cells moving into the interior of the embryo at the blastopore followed by other cells
2. around most of the ventral margins of the blastopore and extending down onto the ventral part of the embryo, the prospective endoderm is rolled into the interior and eventually comes to lie its archenteron or primitive gut
3. most of the cells passing over the dorsal lip of blastopore are called chordamesoderm -> give rise to notochord and cephalic mesoderm

Question 29

layers in blastula of chick embryo

Answer 29

1. epiblast, upper layer
2. primary hypoblast, lower layer

Question 30

where does the embryo proper occupy in birds

Answer 30

transparent area pellucida surrounded by area opaca

Question 31

where the cells of blastoderm lie

Answer 31

area opaca

Question 32

sickle-shaped mass of cells that take shape at the posterior end of the embryo in birds

Answer 32

Koller’s sickle

Question 33

can be considered a pregastrulation phenomenon in birds

Answer 33

formation of primary and secondary hypoblasts

Question 34

how does gastrulation and formation of germ layers begin in birds

Answer 34

appearance of condensation of cells in the posterior part of epiblast

Question 35

what is the thickened area called by the end of 1st half day in bird embryo

Answer 35

primitive streak

Question 36

runs down the center of the primitive streak

Answer 36

primitive groove

Question 37

closely packed cells in the cephalic end of bird embryo

Answer 37

Hensen’s node

Question 38

how are the embryonic germ layers formed in bird embryo

Answer 38

• migration of epiblast toward Hensen’s node and primitive streak
• ingression to form the middle and lower germ layers