Weeks 2 & 3 Development

Question 1

describe week 2

Answer 1

• implantation completed
• trophoblast differentiates into 2 layers
• embryoblast forms 2 layers
• extraembryonic mesoderm splits into 2 layers
• 2 cavities form

Question 2

day 8- trophoblast differentiated

Answer 2

• cytotrophoblast

- syncytiotrophoblast

Question 3

day 8- embryoblast differentiates:

Answer 3

• hypoblast

- epiblast

Question 4

day 8, the _____ forms

Answer 4

amniotic cavity

Question 5

amnioblasts are…

Answer 5

epiblast cells adjacent to cytotrophoblast

Question 6

During day 9, ____ migrate peripherally forming the _____

Answer 6

hypoblast cells; exocoelomic (heuser) membrane

Question 7

the exocoelmic membrane and the hypoblast forms lining of _____

Answer 7

exocoelmic cavity (also called primitive yolk sac or primary umbilical vesicle)

Question 8

During day 9, _____ fills in tiny space in _____

Answer 8

fibrin coagulum; endometrial wall

Question 9

During day 9, _____ appear in syncytium of _____

Answer 9

vacuoles; embryonic pole

Question 10

during day 9, fuse form _____ called the _____

Answer 10

lacunae; lacunar stage

Question 11

During days 11 and 12…

Answer 11

• trophoblast characterized by lacunar spaces in the syncytium; forms intercommunicating network
• Cells of syncytiotrophoblast erode endothelial lining of maternal capillaries; sinusoids
• syncytial lacunae become continuous with sinusoids
• establishes uteroplacental circulation

Question 12

during days 11 and 12, blastocyst is completely _____

Answer 12

embedded in stroma

Question 13

During days 11 and 12, new cells appear between inner surface of ____ and outer surface of _____, forming the _____

Answer 13

cytotrophoblast; exocoelomic cavity; extraembryonic mesoderm

Question 14

days 11 and 12 the cells lining the primary umbilical vesicle form a layer of _____ that surrounds the _____ and ______

Answer 14

extraembryonic mesoderm; amniotic cavity; primary umbilical vesicle (yolk sac)

Question 15

days 11 and 12, large cavities known as the _____ form in _____ and will eventually fuse

Answer 15

extraembryonic coelomic spaces; extraembryonic mesoderm

Question 16

days 11 and 12…

Answer 16

• large cavities form in extraembryonic mesoderm
• form extraembryonic cavity (aka chorionic cavity)
• chorionic cavity surrounds amnion and umbilical vesicle except at connecting stalk

Question 17

the extraembryonic mesoderm lining cytotrophoblast and amnion is _____

Answer 17

extraembryonic somatic mesoderm

Question 18

the extraembryonic mesoderm covering the yolk sac

Answer 18

extraembryonic splanchnic mesoderm

Question 19

day 13

Answer 19

• trophoblast characterized by primary villi
• hypoblast produces cells that form secondary yolk sac (aka definitive yolk sac); exocoelomic cysts in the extraembryonic coelom (chorionic cavity)

Question 20

during day 13, the _____ forms

Answer 20

chorionic cavity

Question 21

extraembryonic mesoderm lining inside of cytotrophoblast

Answer 21

chorionic place

Question 22

_____ will develop into the umbilical cord with development of blood vessels

Answer 22

connecting stalk

Question 23

chorionic cavity surrounds ____ and _____ except at _____

Answer 23

amnion; umbilical vesicle; connecting stalk

Question 24

at the end of week 2, a thickening develops in a region of the ____ where the cells become _____ in shape (this is known as the _____)

Answer 24

hypoblast; columnar; prechordal plate

Question 25

the prechordal plate indicates the future site of the ____

Answer 25

mouth

Question 26

recap of week 2

Answer 26

- implantation completed - uteroplacental circulation established - embryoblast develops into bilaminar disc - amniotic and chorionic cavities form - extraembryonic mesoderm forms - primary and secondary yolk sacs form

Question 27

week 3

Answer 27

- formative of primitive streak and node - gastrulation occurs - formation of notochord - establishment of body axes - growth of the embryo

Question 28

formative process by which the 3 embryonic germ layers are formed

Answer 28

endoderm, mesoderm, ectoderm all formed by gastrulation

Question 29

endoderm, mesoderm, ectoderm all formed from _____

Answer 29

epiblast

Question 30

gastrulation begins with formation of ______

Answer 30

primitive streak

Question 31

cephalic end of primitive streak =

Answer 31

primitive node which surrounds the primitive pit

Question 32

during gastrulation, epiblast cells migrate towards _____ and slip beneath epiblast, which is called _____

Answer 32

primitive streak; invagination

Question 33

invaginating epiblast cells:

Answer 33

- displace/replace hypoblast cells forming endoderm - lie between epiblast and endoderm to form mesoderm - cells remaining in epiblast form ectoderm

Question 34

hypoblast cells are fairly ___ and not ___; the migrating epiblast cells which displace/replace the hypoblast cells are much more ___ and ____; the same goes for the epiblast cells which remain in the epiblast and do not migrate; they will also become more ____ to form the ____

Answer 34

thin; robust; robust; substantial; robust; ectoderm

Question 35

during gastrulation, cells continue to spread ____ and _____; in cephalic direction, pass on each side of _____

Answer 35

laterally; cranially; prechordal plate

Question 36

the prechoral plate is formed between the tip of the ____ and ____

Answer 36

notochord; oropharyngeal membrane (future opening of the oral cavity)

Question 37

during notochord formation, _____ invaginate in the _____ which forms the _____

Answer 37

prenotochordal cells; primitive pit; notochordal process

Question 38

the notochordal process grows cranially from the _____ until it reaches the _____ and acquires a ____, which is known as the ____

Answer 38

primitive node; prechordal plate; lumen; notochordal canal

Question 39

the floor of the _____ fuses with ____ below and it degenerates

Answer 39

notochordal process; endoderm

Question 40

once the floor degenerates, the _____ now has open connection with _____ through what is known as the _____

Answer 40

amniotic cavity; umbilical vesicle; neurenteric canal

Question 41

two other names for extracoelomic cavity

Answer 41

primitive yolk sac and primary umbilical vesicle

Question 42

the notochordal process is basically a hollow tube of _____ which move forward _____ from ____ to _____

Answer 42

prenotochordal cells; cranially; primitive node; prechordal plate

Question 43

remains of notochordal process comprise the _____; this ____ separates from _____, folding in to form the ____

Answer 43

notochordal plate; notochordal plate; endoderm; notochord

Question 44

recap of notochord formation

Answer 44

The ventral floor of the tube fuses with the underlying endoderm and the two layers breakdown, leaving the flattened notochordal plate. (At the level of the primitive pit the yolk sac is transiently communicating with the amniotic cavity thru the neurenteric canal). The notochordal plate then detaches from the endoderm, into the mesoderm containing space between the endoderm and ectoderm, forming a solid rod = notochord.

Question 45

the cloacal membrane is formed at the _____ of the _____

Answer 45

caudal end; embryonic disc

Question 46

cloacal membrane similar to ______

Answer 46

oropharyngeal membrane

Question 47

yolk sac forms _____ that extends into ______; allantois forms around _____

Answer 47

diverticulum; connecting stalk; day 16

Question 48

allantois in lower vertebrates serves as a reservoir for ____ products of the _____; in humans, it remains ____ but may be involved in abnormalities of _____

Answer 48

excretion; renal system; rudimentary; bladder development

Question 49

beginning of week 3, trophoblast is characterized by _____; _____ covered by _____

Answer 49

primary villi; cytotrophoblastic core; syncytial layer

Question 50

further development of trophoblast: _____ penetrate core of primary villi (secondary villus)

Answer 50

mesodermal cells

Question 51

end of 3rd week, mesodermal cells differentiate into ____ and _____

Answer 51

blood cells; small blood vessels (tertiary villus)

Question 52

capillaries in tertiary villi make contact with capillaries developing in _____ of _____ and in ______; contact established with ______, connecting the ____ and ____

Answer 52

mesoderm; chorionic plate; connecting stalk; intraembryonic circulatory system; placenta; embryo

Question 53

blood vessels arise from blood islands

Answer 53

vasculogenesis

Question 54

blood vessels sprouting from existing vessels

Answer 54

angiogenesis

Question 55

____ cavity enlarges; embryo attached to its _____ by narrow _____

Answer 55

chorionic; trophoblastic shell; connecting stalk

Question 56

connecting stalk will develop into the _____ with development of _____

Answer 56

umbilical cord; blood vessels

Question 57

recap of week 3

Answer 57

- formation of primitive streak and node - gastrulation occurs - formation of notochord - establishment of body axes - growth of the embryo - primary to secondary to tertiary villi