The Third Week (Exam 1)

Question 1

What is the appearance of the embryonic disc at the end of the second week

Answer 1

becomes elongated and is broader at the cephalic end

Question 2

What is gastrulation

Answer 2

formation of the three embryonic layers, forms trilaminar embryonic disc

Question 3

What does gastrulation establish

Answer 3

the ectoderm, mesoderm, and endoderm germ layers

Question 4

When will the primitive streak be formed

Answer 4

day 15

Question 5

How is the primitive streak formed

Answer 5

hypoblast cells induce the epiblast cells to proliferate and migrate towards the midline to form a groove

Question 6

Where does the primitive groove appear

Answer 6

along the dorsal midline of the epiblast

Question 7

What occurs to the primitive groove

Answer 7

it deepens

Question 8

After the primitive groove deepens, it forms what

Answer 8

the primitive streak

Question 9

What does the primitive streak have

Answer 9

Primitive pit at the cranial end

Question 10

When does gastrulation occur

Answer 10

Day 16

start using GAS pedal at age 16

Question 11

How will the epiblast form the three germ cell layers during gastrulation

Answer 11

ingressing epiblast cells first displace the hypoblast cells to form the endoderm

some cells of epiblast occupy the space between teh endoderm and the epiblast to form the intraembryonic mesoderm

epiblast cells that do not migrate through are now the ectoderm

Question 12

What will line the yolk sac after gastrulation

Answer 12

endoderm

Question 13

When is the embryo referred to as trilaminar germ disc

Answer 13

After completion of gastrulation

Question 14

What is the trilaminar germ disc composed of

Answer 14

ectoderm
intraembryonic mesoderm
endoderm

Question 15

How is the notochord formed

Answer 15

notochordal process extends from the primitive pit to the prechordal plate

floor of the notochordal process fuses with underlying endoderm and forms a flattened notochordal plate

plate detaches and forms the solid definitive notochord

Question 16

What is the prechordal plate

Answer 16

an area where epiblast and hypoblast are still contact rostrally–toward the head

Question 17

The notochord is composed of what types of cells

Answer 17

endoderm and mesoderm

Question 18

What will form from the prechordal plate

Answer 18

head stuff

Question 19

What will form from the cloacal plate

Answer 19

gut stuff

Question 20

What are the functions of the notochord

Answer 20

directs CNS development
development of the vertebral column (through induction of ectoderm)
determins anatomic midline
forms the nucleus pulposis of IV disc

Question 21

What remnant of the notochord is seen in adults

Answer 21

nucleus pulposis of IV disc

Question 22

What is a neurenteric canal

Answer 22

opening between the amnion and yolk sac at the primitive pit

Question 23

What is the clinical significance of the neurenteric canal

Answer 23

neurenteric cysts may form

Question 24

What are neurenteric cysts

Answer 24

masses of endodermally derived tissue commonly associated with the spinal cord

Question 25

How are the ends of the gut tube formed

Answer 25

two depressions arise in the ectoderm, one at cranial end and one at caudal end and form ends of gut tube

Question 26

What is the depression at the caudal end

Answer 26

cloacal membrane

Question 27

What is the depression at the cranial end

Answer 27

buccopharyngeal membrane

Question 28

What is a longitudinal fold

Answer 28

head to tail folding of the embryo

Question 29

What plane does the longitudinal fold occur in

Answer 29

midsagittal plane

Question 30

What cuases the longitudinal fold to occur

Answer 30

rapid growth of the brain, but slower rate of growth of trunk and limbs

Question 31

What are the major results of the longitudinal fold

Answer 31

reposition of the cardiogenic area, portion of yolk sac becomes incorporated into the embryo to form the gut tube

Question 32

When does longitudinal folding occur

Answer 32

end of 3rd week

Question 33

What is transverse embryonic folding

Answer 33

two lateral edges of ectoderm fuse with each other ventrally

Question 34

What causes transverse embryonic folding

Answer 34

rapid growth of the somites, CNS, and differential cell growth

Question 35

What will embryonic folding results in

Answer 35

tubular embryo (no longer a flat trilaminar embryo)

Question 36

When will the primitive streak regress

Answer 36

after week 4

Question 37

What is holoprosencephaly

Answer 37

abnormal face defects, enlarged brain, deficiency of midline head structures

Question 38

What is holoprosencephaly a result of

Answer 38

innapropriate death of midline cells

Question 39

What causes Ectopia cordis

Answer 39

lateral foldings not complete, did not enclose thoracic organs

Question 40

WHat is ectopia cordis

Answer 40

heart outside chest

Question 41

What are the primitive streak and primitive node essential in

Answer 41

determining body axes

Question 42

What is situs inversus

Answer 42

organs are on opposite side of the body

Question 43

What is complete situs inversus

Answer 43

all organs are mirror image of normal orientation

Question 44

What is incomplete situs inversus

Answer 44

only a single organ is involved

Question 45

What is sirenomelia

Answer 45

lower limbs fused together, caudal dysgenesis

Question 46

What causes sirenomelia

Answer 46

inadequate mesoderm in caudal regions

Question 47

What causes a sacrococcygeal teratoma

Answer 47

persistence of primitive streak and pluripotent cells

Question 48

What is a teratoma

Answer 48

all germ layers present (ectoderm, mesoderm, and endoderm)

Question 49

The third week is known as the week of 3's, what things form

Answer 49

3 layers 3 cavities 3 layers in the villi

Question 50

At the beginning of the third week, what is the embryo composed of

Answer 50

hypoblast and epiblast