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LECOM MS1 Embryology > The Third Week (Exam 1) > Flashcards

The Third Week (Exam 1) Flashcards

1
Q

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

A

becomes elongated and is broader at the cephalic end

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2
Q

What is gastrulation

A

formation of the three embryonic layers, forms trilaminar embryonic disc

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3
Q

What does gastrulation establish

A

the ectoderm, mesoderm, and endoderm germ layers

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4
Q

When will the primitive streak be formed

A

day 15

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5
Q

How is the primitive streak formed

A

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

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6
Q

Where does the primitive groove appear

A

along the dorsal midline of the epiblast

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7
Q

What occurs to the primitive groove

A

it deepens

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8
Q

After the primitive groove deepens, it forms what

A

the primitive streak

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9
Q

What does the primitive streak have

A

Primitive pit at the cranial end

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10
Q

When does gastrulation occur

A

Day 16

start using GAS pedal at age 16

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11
Q

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

A

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

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12
Q

What will line the yolk sac after gastrulation

A

endoderm

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13
Q

When is the embryo referred to as trilaminar germ disc

A

After completion of gastrulation

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14
Q

What is the trilaminar germ disc composed of

A

ectoderm
intraembryonic mesoderm
endoderm

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15
Q

How is the notochord formed

A

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

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16
Q

What is the prechordal plate

A

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

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17
Q

The notochord is composed of what types of cells

A

endoderm and mesoderm

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18
Q

What will form from the prechordal plate

A

head stuff

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19
Q

What will form from the cloacal plate

A

gut stuff

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20
Q

What are the functions of the notochord

A

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

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21
Q

What remnant of the notochord is seen in adults

A

nucleus pulposis of IV disc

22
Q

What is a neurenteric canal

A

opening between the amnion and yolk sac at the primitive pit

23
Q

What is the clinical significance of the neurenteric canal

A

neurenteric cysts may form

24
Q

What are neurenteric cysts

A

masses of endodermally derived tissue commonly associated with the spinal cord

25
Q

How are the ends of the gut tube formed

A

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

26
Q

What is the depression at the caudal end

A

cloacal membrane

27
Q

What is the depression at the cranial end

A

buccopharyngeal membrane

28
Q

What is a longitudinal fold

A

head to tail folding of the embryo

29
Q

What plane does the longitudinal fold occur in

A

midsagittal plane

30
Q

What cuases the longitudinal fold to occur

A

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

31
Q

What are the major results of the longitudinal fold

A

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

32
Q

When does longitudinal folding occur

A

end of 3rd week

33
Q

What is transverse embryonic folding

A

two lateral edges of ectoderm fuse with each other ventrally

34
Q

What causes transverse embryonic folding

A

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

35
Q

What will embryonic folding results in

A

tubular embryo (no longer a flat trilaminar embryo)

36
Q

When will the primitive streak regress

A

after week 4

37
Q

What is holoprosencephaly

A

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

38
Q

What is holoprosencephaly a result of

A

innapropriate death of midline cells

39
Q

What causes Ectopia cordis

A

lateral foldings not complete, did not enclose thoracic organs

40
Q

WHat is ectopia cordis

A

heart outside chest

41
Q

What are the primitive streak and primitive node essential in

A

determining body axes

42
Q

What is situs inversus

A

organs are on opposite side of the body

43
Q

What is complete situs inversus

A

all organs are mirror image of normal orientation

44
Q

What is incomplete situs inversus

A

only a single organ is involved

45
Q

What is sirenomelia

A

lower limbs fused together, caudal dysgenesis

46
Q

What causes sirenomelia

A

inadequate mesoderm in caudal regions

47
Q

What causes a sacrococcygeal teratoma

A

persistence of primitive streak and pluripotent cells

48
Q

What is a teratoma

A

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

49
Q

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

A

3 layers
3 cavities
3 layers in the villi

50
Q

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

A

hypoblast and epiblast

LECOM MS1 Embryology (19 decks)

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