Gastrulation

Question 1

Highly coordinated cell movements that transform the blastula into a gastrula, a three-layered embryo. Establishes ectoderm, mesoderm, and endoderm.

Answer 1

Gastrulation

Question 2

A ball of blastomeres that precedes gastrulation. It is transformed into the gastrula during gastrulation.

Answer 2

Blastula

Question 3

The three-layered embryo formed from the blastula during gastrulation. It contains the ectoderm, mesoderm, and endoderm.

Answer 3

Gastrula

Question 4

The three distinct layers formed during gastrulation: ectoderm, mesoderm, and endoderm. They give rise to all tissues and organs.

Answer 4

Embryonic germ layers

Question 5

The outermost germ layer. Gives rise to the epidermis of the skin, nervous system, and sensory organs.

Answer 5

Ectoderm

Question 6

The middle germ layer. Gives rise to the notochord, skeleton, muscles, kidneys, gonads, dermis, and skeletal components.

Answer 6

Mesoderm

Question 7

The innermost germ layer. Gives rise to the epithelium of the digestive tract, liver, pancreas, and lungs.

Answer 7

Endoderm

Question 8

An inflection or folding inward of a sheet of cells. Example: formation of the blastopore in a sea urchin embryo.

Answer 8

Invagination

Question 9

The inturning or anterior migration of an expanding outer sheet of cells. Example: movement of superficial cells of the epiblast through the primitive streak.

Answer 9

Involution

Question 10

The migration of individual cells from a surface layer into the embryo’s interior. Example: mesoderm formation in sea urchin embryos.

Answer 10

Ingression

Question 11

The splitting of a single sheet of cells into two separate but parallel sheets. Example: formation of the hypoblast in chick and mammalian embryos.

Answer 11

Delamination

Question 12

The spreading of a sheet of cells over another sheet or surface. Example: migration of ectoderm over the surface of the amphibian embryo.

Answer 12

Epiboly

Question 13

The movement of cells towards a common central point. Example: formation of the primitive streak.

Answer 13

Convergence

Question 14

The rearrangement and elongation of a cluster of cells to form a thin, stretched cellular group. Example: formation of the notochord.

Answer 14

Extension

Question 15

A simple type of gastrulation that occurs soon after the blastula hatches. The vegetal plate flattens and invaginates into the blastocoel.

Answer 15

Sea Urchin Gastrulation

Question 16

A flattened region at the vegetal pole of the sea urchin blastula. Site of invagination during gastrulation.

Answer 16

Vegetal plate

Question 17

The fluid-filled cavity inside the blastula. The archenteron extends into it during sea urchin gastrulation.

Answer 17

Blastocoel

Question 18

The primitive gut formed by the invagination of the vegetal plate in sea urchins. Located inside the blastocoel.

Answer 18

Archenteron (aka Gastrocoel)

Question 19

The external opening of the archenteron. Becomes the anus in sea urchins.

Answer 19

Blastopore

Question 20

An invagination that meets the archenteron to form the mouth.

Answer 20

Stomodeum

Question 21

The side of the embryo where the stomodeum forms the mouth.

Answer 21

Oral side

Question 22

The side of the embryo where the blastopore forms the anus.

Answer 22

Aboral side

Question 23

The larval stage of the sea urchin. Develops from the gastrula. Has skeletal rods for support.

Answer 23

Pluteus larva

Question 24

Structures formed by mesenchymal cells in the sea urchin larva. Composed of CaCO₃ (magnesium calcite), provide support for larval arms.

Answer 24

Skeletal rods

Question 25

Cells that originate from the micromeres in the sea urchin blastula. Ingress first during gastrulation.

Answer 25

Primary mesenchyme cells

Question 26

Cells located at the tip of the archenteron in the sea urchin larva. Ingress later than primary mesenchyme cells; help guide archenteron elongation.

Answer 26

Secondary mesenchyme cells

Question 27

The sea urchin larva stage that develops from the gastrula. Has skeletal rods, swims freely, feeds, and later metamorphoses into a small adult sea urchin.

Answer 27

Pluteus

Question 28

A more complex type of gastrulation than sea urchins. Begins dorsally at the marginal zone and involves coordinated cell movements.

Answer 28

Amphibian Gastrulation

Question 29

The region where amphibian gastrulation begins.

Answer 29

Marginal zone

Question 30

The initial site where gastrulation begins in amphibians. Formed by bottle cells; cells invaginate through this lip.

Answer 30

Dorsal lip of the blastopore

Question 31

Cells at the dorsal lip of the amphibian blastopore that change shape (bottle-shaped) to initiate invagination.

Answer 31

Bottle cells

Question 32

Forms later as the amphibian blastopore extends.

Answer 32

Ventral lip of the blastopore

Question 33

Also form later as the amphibian blastopore extends.

Answer 33

Lateral lips of the blastopore

Question 34

Refers to the edges of the blastopore in amphibians. Cells of the involuting marginal zone (IMZ) move through it.

Answer 34

Blastopore lip

Question 35

Cells that involute through the blastopore lip in amphibians. These cells become the mesoderm and endoderm.

Answer 35

IMZ (Involuting Marginal Zone)

Question 36

Formed by large, yolky endoderm cells that fill the blastopore opening in amphibians. Becomes internalized as the blastopore closes.

Answer 36

Yolk plug

Question 37

The dorsal lip of the blastopore in amphibians. Considered the site of the future anus and acts as an organizer, inducing surrounding cells.

Answer 37

Spemann organizer

Question 38

Gastrulation that occurs within the blastodisc, specifically in the epiblast. Begins with the formation of the primitive streak.

Answer 38

Avian Gastrulation

Question 39

The structure within which avian gastrulation occurs.

Answer 39

Blastodisc

Question 40

The upper layer of the avian blastodisc. All three germ layers and most extraembryonic membranes are derived from the epiblast in birds and mammals.

Answer 40

Epiblast

Question 41

A longitudinal thickening formed in the epiblast. Site where epiblast cells ingress to form mesoderm and endoderm. Regresses caudally over time.

Answer 41

Primitive streak

Question 42

The tail region of the embryo. The primitive streak is visible here in later stages.

Answer 42

Caudal region

Question 43

The head region of the embryo. Hensen's node is located in the cranial part of the primitive streak.

Answer 43

Cranial region

Question 44

A depression that forms along the length of the primitive streak. Cells move through this groove.

Answer 44

Primitive groove

Question 45

The elevated edges that flank the primitive groove.

Answer 45

Primitive folds

Question 46

Cells that migrate through the primitive streak in birds are referred to as mesenchyme.

Answer 46

Mesenchyme

Question 47

The lower layer of the avian blastodisc. Does not contribute to the embryo proper but forms extraembryonic membranes.

Answer 47

Hypoblast

Question 48

The cranial-most part of the primitive streak. Considered the avian organizer; cells ingressing here form the notochord.

Answer 48

Hensen's node (Primitive knot)

Question 49

A rod-like structure formed from cells that ingress through Hensen's node.

Answer 49

Notochord

Question 50

The central translucent area of the blastodisc where the embryo proper develops.

Answer 50

Area pellucida

Question 51

The peripheral opaque area surrounding the area pellucida.

Answer 51

Area opaca

Question 52

A structure developing in the embryo.

Answer 52

Neural tube

Question 53

A cavity located beneath the blastodisc.

Answer 53

Subgerminal cavity

Question 54

Refers to the head end of the blastoderm.

Answer 54

Cranial blastoderm

Question 55

Refers to the tail end of the blastoderm.

Answer 55

Caudal blastoderm

Question 56

A subdivision of the mesoderm.

Answer 56

Lateral mesoderm

Question 57

A subdivision of the mesoderm.

Answer 57

Somatic mesoderm

Question 58

A subdivision of the mesoderm.

Answer 58

Splanchnic mesoderm