Lec.7 GASTRULATION

Question 1

As discussed before, ____ leads to the formation of the three germ layers: ecto-, endo- and mesoderm.

Gastrulation also establishes the germ line, in the form of the ____

Answer 1

gastrulation

primordial germ cells

Question 2

While gastrulation proceeds, the embryonic disc gradually becomes covered by extra-embryonic membranes to form the ____

In domestic species, amnion formation results from an ‘upfolding’ of the ____ with its underlying extra- embryonic mesoderm.

Answer 2

amniotic cavity

trophectoderm

Question 3

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.

Answer 3

chorion

Question 4

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, the amnion will become surrounded by yet another cavity, the ____

Answer 4

amnion

allantois

Question 5

The onset of gastrulation is linked to the appearance of the ____

The epiblast cells accumulate ____ and thickens in the embryonic disc.

Answer 5

primitive streak

posteriorly

Question 6

*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 ____

Answer 6

mes-endodermal precursors

endoderm

Question 7

*Primitive streak
The endoderm enlarges to form the ____ of the primitive yolk sac and is continuous with the hypoblast.

Answer 7

upper lining

Question 8

*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 ____

Answer 8

primitive gut

yolk sac

Question 9

*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.

Answer 9

epiblast and trophectoderm

endoderm and hypoblast

Question 10

*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 ____

Answer 10

coelom

extra-embryonic coelom or exocoelom.

Question 10

*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

Answer 10

intra-embryonic coelom

Question 11

*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

Answer 11

pear- shaped

posteriorly

Question 12

*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 ____

Answer 12

notochord

primitive node

Question 13

*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 ____

Answer 13

neural plate

neural folds

neural groove

Question 14

*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 ____

Answer 14

neural tube

central nervous system

Question 15

*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.

Answer 15

neural crest cells

Question 16

*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).

Answer 16

melanocytes

Question 17

*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.

Answer 17

surface ectoderm

otic placode and lens placode

Question 18

*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

Answer 18

otic vesicle

lens

Question 19

*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.

Answer 19

epidermis

glands

enamel

Question 20

*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.

Answer 20

somitomeres

Question 21

*Mesoderm
In the body region, they form ____ from which dermis, skeletal muscle and vertebrae develop.

Formation of somites progresses from the occipital region posteriorly.

Answer 21

somites

Question 22

*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 ____

Answer 22

vertebral column

dermamyotome

Question 23

*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).

Answer 23

myotome

dermatome

Question 24

*Mesoderm
The ____ connects the paraxial and lateral plate mesoderm.

It differentiates into structures of both the urinary system and the gonads (urogenital system).

Answer 24

intermediate mesoderm

Question 25

*Mesoderm
The intermediate mesoderm in the cervical and cranial thoracic regions forms ____

Caudally the nephrogenic cord is formed, that will be a temporary kidney, the ____

In the medial aspect, the gonads start to form in order to receive the PGCs.

Answer 25

nephrotomeres

mesonephros

Question 26

*Mesoderm
The ____ will provide all other components of the gut (that are not derived from endoderm) and its derivatives.

Both blood and blood vessels appear to arise from the ____

These differentiate into ____ stem cells (forming blood cells) and ____ (forming blood vessels).

Answer 26

visceral mesoderm

hemangioblasts

hematopoietic stem cells

angioblasts

Question 27

*Endoderm
The inner epithelial lining of the gastrointestinal tract and its derivatives are derived from the ____

The endoderm-enclosed portion of the primitive yolk sac is enclosed within the embryo forming the ____, whereas the hypoblast-enclosed portion becomes localized outside the embryo to form the definitive ____

Answer 27

endoderm

primitive gut

yolk sac

Question 28

*Endoderm
The primitive gut comprises cranial (foregut), middle (midgut) and caudal (hindgut) parts.

Endoderm of the foregut gives rise to: (6)

Answer 28

pharynx

middle ear

esophagus

stomach

liver

pancreas

Question 29

*Endoderm
The ____ gives rise to most of the small and the large intestine down to the transverse colon.
This also connects with the yolk sac through the ____

The ____ gives rise to the transverse and descending colon as well as the rectum and part of the anal canal.

Answer 29

midgut

vitelline duct

hindgut

Question 30

*Endoderm
During the ____ week of development, the allantois is formed as an outgrowth from the hindgut into the extraembryonic coelom.

The allantoic duct along with the vitelline duct becomes incorporated into the ____

Answer 30

second or third week

umbilical cord

Question 31

*Primordial germ cell
During formation of the mesoderm and endoderm, a certain population of epiblast cells is set aside for formation of the future ____

As the somatic germ layers form, the primordial germ cells are displaced from the embryonic disc area to the wall of the definitive yolk sac and, to some degree, of the allantois.

Answer 31

germ line

Question 32

The PGCs multiply in the yolk sac wall and then relocate into the ____

The PGCs continue to multiply for a while until they either initiate meiosis (female embryo) or enter mitotic arrest until puberty (male embryo).

This ends the gastrulation stage.

Answer 32

developing gonads